In concluding this note, we take the opportunity of recommending all

those who feel interested in the researches of geology, to read a work

lately published, entitled “THE WONDERS OF GEOLOGY, by Gideon Mantell,

LL.D. F.R.S. &c.”

Note 20, p. 137.--THE RIFLE.

Rifle guns are those whose barrels, instead of being smooth on the

inside, like our common pieces, are formed with a number of spiral

channels, resembling screws; except only that the threads, or rifles,

are less deflected, making only one turn, or a little more, in the

whole length of the piece. This construction is employed for correcting

the irregularity in the flight of balls from smooth barrels, by

imparting to the balls a rotatory motion perpendicular to the line of

direction. The same effect has lately been accomplished by an extremely

simple and obvious contrivance, and which will, probably, altogether

supersede the necessity of rifling the barrel. It consists in cutting a

spiral groove in the bullet itself, which, when discharged, is thus

acted upon by the air, and the same rotatory motion imparted to it as

that produced by the furrows in the barrel. But it is the rotatory

motion which steadies the flight of the ball; and by whichever method

this is produced, the theory of its action will be the same. It has

been long and generally known, that when the common bullet is

discharged from a plane barrel, its flight is extremely irregular and

uncertain; it has, for instance, been found, from the experiments of

Mr. Robins, that, notwithstanding the piece was firmly fixed, and fired

with the same weight of powder, the ball was sometimes deflected to the

right, sometimes to the left, sometimes above, and at others below the

true line of direction. It has also been observed, that the degree of

deflection increases in a much greater proportion than the distance of

the object fired at. It is not difficult to account for these

irregularities; they, doubtless, proceed from the impossibility of

fitting a ball so accurately to any plane piece, but that it will rub

more against one side of the barrel than another in its passage through

it. Whatever side, therefore, of the muzzle, the ball is last in

contact with, on quitting the piece, it will acquire a whirling motion

towards that side, and will be found to bend the line of its flight in

the same direction, whether it be upwards or downwards, to the right or

left; or obliquely, partaking in some degree of both; and, after

quitting the barrel, this deflection, though in the first instance but

trifling and inconsiderable, is still farther increased by the

resistance of the air; this being greatest on that side where the

whirling motion conspires with the progressive one, and least on that

side where it is opposed to it. Thus, if the ball, in its passage out,

rubs against the left side of the barrel, it will whirl towards that

side; and as the right side of the ball will, therefore, turn up

against the air during its flight, the resistance of the air will

become greatest on the right side, and the ball be forced away to the

left, which was the direction it whirled in. It happens, moreover, from

various accidental circumstances, that the axis of the ball’s rotation

frequently changes its position several times during the flight; so

that the ball, instead of bending its course uniformly in the same

direction, often describes a track variously contorted. From this view

of the causes of aberration in the flight of balls, it will be evident

that the only means of correcting it is by preventing the ball from

rubbing more against one side of the barrel than another in passing

through it; and by giving to the bullet a motion which will counteract

every accidental one, and preserve its direction, by making the

resistance of the air upon the forepart continue the same during its

whole flight; that is, by giving it a rotatory motion perpendicular to

the line of direction. The contrivance for this purpose is called

_rifling_, and consists, as we have before stated, in forming upon the

inside of the barrel a number of threads and furrows, either in a

straight or spiral direction, into which the ball is moulded; and

hence, when the gun is fired, the indented zone of the bullet follows

the sweep of the rifle, and thereby, besides its progressive motion,

acquires a considerable one round the axis of the barrel, which motion

will be continued to the bullet after its separation from the piece, so

that it is constantly made to whirl round an axis coincident with the

line of its flight. Many familiar examples of the utility and effect of

_rifling_ might be here adduced. If the bricklayer, while unroofing a

house, be observed, he will be seen to give to the slates which he

throws down a whirling motion, at a certain angle, which ensures their

falling edgeways on the ground, and thus preserves them from fracture.

In relation to the subject in the text, to which this note refers, may

be introduced a notice of the “BOMMERENG,” a missile used by the

natives of Australia, and thus described by Major Mitchell in his

“_Journal of an expedition to the Rivers Darling and Murray._” “The

bommereng, a thin, curved missile, about two feet four inches long, can

be thrown by a skilful hand so as to rise upon the wind with a rotatory

motion, and in a crooked direction towards any given point with great

precision, and to return, after a considerable flight, to within a yard

or two of the thrower; or, by striking the ground near him, to bound so

as to hit at a great, distance, “_en ricochet_” any object behind a

tree. This singular weapon probably originated in the utility of such a

missile for the purpose of killing ducks, where they are very numerous,

as on the interior rivers and lagoons, and where we accordingly find it

much more in use than on the sea coast, and better made, being often

covered with good carving.” This instrument may now be purchased in

most of the London toy-shops.

Note 21, p. 144.--CENTRE OF PERCUSSION.

If a stick be held at one of its extremities, and allowed to fall on

the edge of a table, the farther end will rebound, or the hand will

sustain a shock, unless it be struck exactly on the centre of

percussion, in which case the stick will fall as a dead weight. The

repetition of this simple experiment will readily convey to the young

philosopher an idea of the nature of what is termed the _centre of

percussion_.

Note 22, p. 150.--SPINNING OF THE TOP.

It has been stated in the text, that the gyrations of the top depend

exactly upon the same principle as that which produces the _precession

of the equinoxes_; viz. an unequal attractive force exerted upon the

revolving mass. In the one case, this is known to arise from the action

of the sun and moon on the excess of matter about the equatorial

regions of the earth; in the other, from the parts of the top being

unequally affected by gravity, while it is spinning in an inclined or

oblique position. To those philosophers who have condescended to read

the present work, if there be any such, and are thereby induced to

pursue the investigation of a subject which has hitherto excited far

too little attention, we beg to submit the following remarks:--

If a top could be made to revolve on a point without friction, and in a

vacuum, in the case of its velocity being _infinite_, it would continue

to revolve for ever, in the same position, without gyration. If the

velocity were _finite_, it would for ever remain unchanged in position,

in the event of the centre of gravity being directly over the point of

rotation. In any other position (supposing its velocity very great,

although not infinite) there would arise a continued uniform gyration;

the line which passes through the point of rotation, and the centre of

gravity, always making the same angle with the horizon, or describing

the same circle round the zenith. But in all artificial experiments the

circumstances are very remarkably changed; if, indeed, the centre of

gravity happens to be situated perpendicularly over the point of

rotation, the top will continue quite steady, or _sleeping_, as it is

termed, till nearly the whole of its velocity of rotation is expended.

In any other position the top begins to gyrate, but reclining at all

times on the outside of its physical point of gyration, the top is

uniformly impelled inwards; and this (when the velocity is

considerable, and the point broad) acts with a force sufficient for

carrying the top towards its quiescent or _sleeping_ point; but when

the velocity is much diminished, this power becomes feeble, the

gyrations increase in diameter, and the top ultimately falls.

Note 23, p. 161.--THE MECHANICAL POWERS.

The mechanical powers are all founded upon the principle that _the

lengths of circles are in proportion to their diameters_; for it is an

immediate consequence of this property of the circle, that if a rod of

iron, or beam of wood, be placed on a point or pivot, so that it may

move round its prop, the two ends will go through parts of circles,

each proportioned to that arm of the beam to which it belongs; the two

circles will be equal if the pivot is in the centre or middle point of

the beam; but if it is nearer one end than the other, say five times,

that end will pass through a circular space, or _arc_, five times

shorter than the circular space the other end goes through in the same

time. If, then, the end of the long beam goes through five times the

space, it must move with five times the swiftness of the short end,

since both move in the same time; and, therefore, any force applied to

the long end must overcome the resistance of five times that force

applied at the opposite end, since the two ends move in contrary

directions; hence one pound placed at the long end would balance five

placed at the short end.

The beam we have been describing constitutes the first of the

mechanical powers, and is termed the LEVER. There are, besides, five

others, viz. the _wheel and axle_; the _inclined plane_; the _screw_;

the _pulley_; and the _wedge_; out of the whole, or a part of which, it

will be found that every mechanical engine or piece of machinery is

constructed.

THE LEVER being the simplest of all the mechanic powers, is in general

considered the first. It is an inflexible rod or bar of any kind, so

disposed as to turn on a pivot or prop, which is always called its

_fulcrum_. It has the weight or resistance to be overcome attached to

some one part of its length, and the power which is to overcome that

resistance applied to another; and, since the _power_, _resistance_,

and _fulcrum_ admit of various positions with regard to each other, so

is the lever divided into three kinds or modifications, distinguished

as the first, second, and third kinds of lever. That portion of it

which is contained between the fulcrum and the power, is called the

acting part or arm of the lever; and that part which is between the

fulcrum and resistance, its resisting part or arm.

In the lever of the first kind, the fulcrum is placed between the power

and the resistance. A poker, in the act of stirring the fire, well

illustrates this subject; the bar is the _fulcrum_, the hand the power,

and the coals the resistance to be overcome. Another common application

of this kind of lever is the crow-bar, or hand-spike, used for raising

a large stone or weight. In all these cases power is gained in

proportion as the distance from the fulcrum to the power, or part where

the men apply their strength, is greater than the distance from the

fulcrum to that end under the stone or weight. A moment’s reflection

will show the rationale of this fact; for it is evident that if both

the arms of the lever be equal, that is to say, if the fulcrum be

midway between the power and weight, no advantage can be gained by it,

because they pass over equal spaces in the same time; and, according to

the fundamental principle already laid down, _as advantage or power is

gained, time must be lost_; but, since no time is lost under such

circumstances, there cannot be any power gained. If, now, we suppose

the fulcrum to be so removed towards the weight, as to make the acting

arm of the lever three times the length of the resisting arm, we shall

obtain a lever which gains power in the proportion of three to one,

that is, a single pound weight applied at the upper end will balance

three pounds suspended at the other. A pair of scissors consists of two

levers of this kind, united in one common fulcrum; thus the point at

which the two levers are screwed together is the fulcrum; the handles

to which the power of the fingers is applied, are the extremities of

the acting part of the levers, and the cutting part of the scissors are

the resisting parts of the levers; the longer, therefore, the handles,

and the shorter the points of the scissors, the more easily you cut

with them. A person who has any hard substance to cut, without any

knowledge of the theory, diminishes as much as possible the length of

the resisting arms, or cutting part of the scissors, by making use of

that part of the instrument nearest the screw or rivet. Snuffers are

levers of a similar description; so are most kind of pincers, the power

of which consists in the resisting arm being very short in comparison

with the acting one.

In the lever of the second kind, the resistance or weight is between

the fulcrum and the power. Numberless instances of its application

daily present themselves to our notice; amongst which may be enumerated

the common cutting knife, used by last and patten makers, one end of

which is fixed to the work-bench by a swivel-hook. Two men carrying a

load between them, by one or more poles, as a sedan chair, or as

brewers carrying a cask of beer, in which case either the back or front

man may be considered as the fulcrum, and the other as the power. Every

door which turns upon its hinges is a lever of this kind; the hinges

may be considered as the fulcrum, or centre of motion; the whole door

is the weight to be moved, and the power is applied to that side on

which the handle is usually fixed. Nut-crackers, oars, rudders of

ships, likewise fall under the same division. The boat is the weight to

be moved, the water is the fulcrum, and the waterman at the oar is the

power. The masts of ships are also levers of the second kind, for the

bottom of the vessel is the fulcrum, the ship the weight, and the wind

acting against the sail is the moving power. In this kind of lever the

power or advantage is gained in proportion as the distance of the power

is greater than the distance of the weight from the fulcrum; if, for

instance, the weight hang at one inch from the fulcrum, and the power

acts at five inches from it, the power gained is five to one; because,

in such a case, the power passes over five times as great a space as

the weight. It is thus evident why there is considerable difficulty in

pushing open a heavy door, if the hand is applied to the part next the

hinges, although it may be opened with the greatest ease in the usual

method. In the third kind of lever, the fulcrum is again at one of the

extremities, the weight or resistance at the other; and it is now the

power which is applied between the fulcrum and resistance. As in this

case the weight is farther from the centre of motion than the power,

such a lever is never used, except in cases of absolute necessity, as

in the case of lifting up a ladder perpendicularly, in order to place

it against a wall. The man who raises it cannot place his hands on the

upper part of the ladder; the power, therefore, is necessarily placed

much nearer the fulcrum than the weight; for the hands are the power,

the ground the fulcrum, and the upper part of the ladder the weight.

The use of the common fire-tongs is another example, but the

circumstance that principally gives this lever importance is, that the

limbs of men and animals are actuated by it; for the bones are the

levers, while the joints are the fulcra, and the muscles which give

motion to the limbs, or produce the power, are inserted and act close

to the joints, while the action is produced at the extremities; the

consequence of such an arrangement is, that although the muscles must

necessarily exert an enormous contractile force to produce great action

at the extremities, yet a celerity of motion ensues which could not be

equally well provided for in any other manner. We may adduce one

example in illustration of this fact. In lifting a weight with the

hand, the lower part of the arm becomes a lever of the third kind; the

elbow is the fulcrum; the muscles of the fleshy part of the arm the

power; and as these are nearer to the elbow than the hand, it is

necessary that their power should exceed the weight to be raised. The

disadvantage, however, with respect to power, is more than compensated

by the convenience resulting from this structure of the arm; and it is

no doubt that which is best adapted to enable it to perform its various

functions. From these observations it must appear, that although this

arrangement must be mentioned as a modification of the lever, it

cannot, in strictness, be called a mechanical power; since its

resisting arm is in all cases, except one, longer than the acting arm,

and in that one case is equal to it, on which account it never can gain

power, but in most instances must lose it.

THE WHEEL AND AXLE is the next mechanical power to be considered; it

must be well known to every reader who has seen a village well; for it

is by this power that the bucket is drawn up, although in such cases,

instead of a wheel attached to the axle, there is generally only a

crooked handle, which answers the purpose of winding the rope round the

axle, and thus raising the bucket, as may be seen in the engraving at

the head of our third chapter. It is evident, however, that this

crooked handle is equivalent to a wheel; for the handle describes a

circle as it revolves, while the straight piece which is united to the

axle corresponds with the spoke of a wheel. This power may be resolved

into a lever; in fact, what is it but a lever moving round an axle? and

always retaining the effect gained during every part of the motion, by

means of a rope wound round the butt end of the axle; the spoke of the

wheel being the long arm of the lever, and the half diameter of the

axle its short arm. The axle is not in itself a mechanical power, for

it is as impotent as a lever whose fulcrum is in the centre; but add to

it the wheel, and we have a power which will increase in proportion as

the circumference of the wheel exceeds that of the axle. This arises

from the velocity of the circumference being so much greater than that

of the axle, as it is farther from the centre of motion; for the wheel

describes a great circle in the same space of time that the axle

describes a small one; therefore the power is increased in the same

proportion as the circumference of the wheel is greater than that of

the axle. Those who have ever drawn a bucket from a well by this

machine, must have observed, that as the bucket ascended nearer the top

the difficulty increased: such an effect must necessarily follow from

the views we have just offered; for whenever the rope coils more than

once the length of the axle, the difference between its circumference

and that of the wheel is necessarily diminished. To the principle of

the wheel and axle may be referred the capstan, windlass, and all those

numerous kinds of cranes which are to be seen at the different wharfs

on the banks of the river Thames. It is scarcely necessary to add that

the force of the windmill depends upon a similar power. The _treadmill_

furnishes another striking example. The wheel and axle is sometimes

used to multiply motion, instead of to gain power, as in the

multiplying wheel of the common jack, to which it is applied when the

weight cannot conveniently have a long line of descent; a heavy weight

is in this case made to act upon the axle, while the wheel, by its

greatest circumference, winds up a much longer quantity of line than

the simple descent of the weight could require, and thus the machine is

made to go much longer without winding than it otherwise would do.

THE PULLEY is a power of very extensive application. Every one must

have seen a pulley; it is a circular and flat piece of wood or metal,

with a string which runs in a groove round it. Where, however, this is

fixed, it cannot afford any power to raise a weight; for it is evident

that, in order to raise it, the power must be greater than the weight,

and that if the rope be pulled down one inch, the weight will only

ascend the same space; consequently, there cannot be any mechanical

advantage from the arrangement. This, however, is not the case where

the pulley is not fixed. Suppose one end of the rope be fastened to a

hook in the ceiling, and that to the moveable pulley on the rope a cask

be attached, is it not evident that the hand applied to the other

extremity of the rope will sustain it more easily than if it held the

cask suspended to a cord without a pulley? Experience shows that this

is the fact, and theory explains it by suggesting that the fixed hook

sustains half the weight, and that the hand, therefore, has only the

other half to sustain. The hook will also afford the same assistance in

raising the weight as in sustaining it; if the hand has but one half

the weight to sustain, it will also have only one half the weight to

raise; but observe, says Mrs. Marcet, that in raising the weight, the

velocity of the hand must be double that of the cask; for, in order to

raise the weight one inch, the hand must draw each of the strings one

inch; the whole string is therefore shortened two inches, while the

weight is raised only one. Pulleys then act on the same principle as

the lever, the deficiency of strength of the power being compensated by

its superior velocity. It will follow, from these premises, that the

greater the number of pulleys connected by a string, the more easily

the weight is raised, as the difficulty is divided amongst the number

of strings, or rather of parts into which the string is divided by the

pulleys. Several pulleys, thus connected, form what is called a system,

or tackle of pulleys. They may have been seen suspended from cranes, to

raise goods into warehouses, and in ships to draw up the sails.

THE INCLINED PLANE is a mechanic power which is seldom used in the

construction of machinery, but applies more particularly to the moving

or raising of loads upon slopes or hills, as in rolling a cask up or

down a sloping plank into or out of a cart or cellar, or drawing a

carriage up a sloping road or hill, all which operations are performed

with less exertion than would be required if the same load were lifted

perpendicularly. It is a power which cannot be resolved into that of

the lever: it is a distinct principle, and those writers who have

attempted to simplify the mechanical powers, have been obliged to

acknowledge the inclined plane is elementary. The method of estimating

the advantage gained by this mechanical power is very easy; for just as

much as the length of the plane exceeds its perpendicular height, so

much is the advantage gained; if, for instance, its length be three

times greater than its height, a weight could be drawn to its summit

with a third part of the strength required for lifting it up at the

end; but, in accordance with the principle so frequently alluded to,

such a power will be at the expense of time, for there will be three

times more space to pass over. The reason why horses are eased by

taking a zig-zag direction, in ascending or descending a steep hill,

will appear from the preceding account of the action of the inclined

plane, because in this way the effective length of the inclining

surface is increased while its height remains the same.

THE WEDGE is rather a compound, than a distinct mechanical power; since

it is composed of two inclined planes, and in action frequently

performs the functions of a lever. It is sometimes employed in raising

bodies; thus the largest ship may be raised to a small height by

driving a wedge below it; but its more common application is that of

dividing and cleaving bodies. As an elevator, it resembles exactly the

inclined plane; for the action is obviously the very same, whether the

wedge be pushed under the load, or the load be drawn under [sic] the

wedge. But when the wedge is drawn forward, the percussive tremor

excited destroys, for an instant, the adhesion or friction at its

sides, and augments prodigiously the effect. From this principle

chiefly is derived the power of the wedge in rending wood and other

substances. It then acts besides as a lever, insinuating itself into

the cleft as fast as the parts are opened by the vibrating concussion.

To bring the action of the wedge, therefore, under a strict

calculation, would be extremely difficult, if not impossible. Its

effects are chiefly discovered by experience. All the various kinds of

cutting tools, such as axes, knives, chisels, saws, planes, and files,

are only different modifications of the wedge.

THE SCREW is a most efficient mechanic power, and is of great force and

general application. It is in reality nothing more than an inclined

plane formed round a cylinder, instead of being a continued straight

line. Its power is, therefore, estimated by taking its circumference,

and dividing this by the distance between any two of its threads; for

what is taking the circumference of a screw, but another mode of

measuring the length of the inclined plane which wraps round it? and

taking the distance between one thread and the next to it, is but

measuring the rise of that inclined plane in such length; and from the

properties of the inclined plane, it follows, that the closer the

threads of a screw are together in proportion to its diameter, the

greater will be the power gained by it.

Note 24, p. 165.--THE CYCLOID.

A _cycloid_ is a peculiar curve line; and is described by any one point

of a circle as it rolls along a plane, and turns round its centre;

thus, for instance, the nail on the felly of a cart-wheel traces a

cycloid in the air as the wheel proceeds. This curve is distinguished

by some remarkable properties, the most important of which is that

mentioned in the text, viz. that any body moving in such a curve, by

its own weight, or swing, will pass through all distances of it in

exactly the same time; and it is for such a reason that pendulums are

made to swing in cycloids, in order that they may move in equal times,

whether they go through a long or a short part of the same curve. Where

the arc described is small, a portion of the circle will be

sufficiently accurate, because it will be seen that such an arc will

not deviate much from an equal portion of a cycloidal curve.

The cycloid is remarkable as being that path, with the exception of the

perpendicular, through which a body will move with the greatest

velocity; suppose, for example, a body is to descend from any one point

to any other, by means of some force acting on it, together with its

weight: a person unacquainted with mechanics would say at once, that a

straight line is the path it must take to effect this in the shortest

possible time, since that is the shortest of all lines that can be

drawn between two points. Undoubtedly it is the shortest;

notwithstanding which, however, the body would be longer in traversing

it, than in moving through a cycloid. If a body were to move through a

space of fifty or a hundred yards, by its weight and some other force

acting together, the way it must take to do this in the shortest

possible time is by moving in a cycloid. It is supposed that birds

which build in the rocks possess an instinctive knowledge of this fact,

and drop or fly down from height to height in this course. There is

certainly a general resemblance between the curved path they describe

on such occasions, and the cycloid, but it would be difficult to

establish the fact by experiment. Man, however, has founded upon this

principle some applications of great value in practical mechanics. In

Switzerland, and in several parts of Germany, for example, slides have

been constructed along the sides of mountains, by which the timber

felled near their summits is conducted with extreme rapidity to the

distant valleys.

Note 25, p. 171.--BILLIARDS.

This interesting game is of French origin (_billiard_, of _bile_, and

from the Latin, _pila_, a ball). It was hailed as a favourite diversion

at the court of Henry III. of France; and was thence communicated to

all the courts of modern Europe. To the novice it may appear as a game

of accidents and chances, but experience has enabled us to determine

the effects of the stroke given to a ball with wonderful precision; and

it is quite extraordinary to observe the accuracy with which an

accomplished player can effect his object, by measuring with his eye

the angle at which he should make the stroke, the position of the ball

with respect to the cushion, and the distance of the point of the ball

from its centre, at which it should be struck. By such skilful

management the ball may be made to take directions which would, at

first view, be regarded as contrary to all the known laws of motion,

such, for instance, as passing round an object, such as a hat placed on

the table, and to strike a ball behind it into a pocket.

Upon this subject the reader should consult a work by M. Mingaud, which

has been translated and published by John Thurston, the celebrated

billiard-table maker of Catherine Street, Strand. We understand that a

still more complete work may be expected from the same source.

Note 26, p. 172.--COLLISION OF BODIES.

In investigating the effects produced upon bodies by collision, it is

necessary to distinguish between elastic and non-elastic substances,

since their motions after impact are governed by very different laws.

If two bodies, _void of elasticity_, move in one right line, either the

same or contrary ways, so that one body may strike directly against

another, let the _sum_ of their motions before the stroke, if they move

the same way, and the _difference_ of their motions, if contrary ways,

be divided into two such parts as are proportional to the quantities of

matter in the bodies, and each of those parts will respectively exhibit

the motion of each body after the stroke: for example, if the

quantities of matter in the bodies be as _two_ to _one_, and their

motions before the stroke as _five_ and _four_, then the sum of their

motions is _nine_, and the difference is _one_; and therefore, when

they move the same way, the motion of that body, which is as _two_,

will, after the stroke, be _six_, and the motion of the other, _three_;

but, if they move in contrary directions, the motion of the greater

body after the stroke will be _two-thirds of one_, and of the lesser

body _one-third of one_; for, since the bodies are void of elasticity,

they will not separate after the stroke, but move together with one and

the same velocity; and, consequently, their motions will be

proportional to their quantities of matter; and it follows from the

fact of action and reaction being equal, that no motion is either lost

or gained by the stroke when the bodies move the same way; because,

whatever motion one body imparts to the other, so much must it lose of

its own; and, consequently, the _sum_ of their motions before the

stroke is neither increased nor diminished by the stroke, but is so

divided between the bodies, as that they may move together with one

common velocity; that is, it is divided between the bodies in

proportion to their quantities of matter: but it is otherwise, where

the bodies move in opposite directions, or contrary ways, for then the

smaller motion will be destroyed by the stroke, as also an equal

quantity of the greater motion, because action and reaction are equal;

and the bodies, after the stroke, will move together equally swift,

with the _difference_ only of their motions before the stroke;

consequently, that difference is, by means of the stroke, divided

between them in proportion to their quantities of matter.

The several particular cases, concerning the collision of bodies, may

be reduced to four general ones; viz.

1st. It may be, that one body only is in motion at the time of the

stroke.

2nd. They may both move one and the same way.

3rd. They may move in direct opposition to each other, and that with

equal quantities of motion.

4th. They may be carried with unequal motions in directions contrary to

each other.

As the bodies may be either equal or unequal, each of these four

general cases may be considered as consisting of two branches.

As to the first, if a body in motion strikes another equal body at

rest, they will, according to the proposition, move together each of

them with one half of the motion that the body had which was in motion

before the stroke; and since the quantity of motion in any body is as

the product arising from the multiplication of its quantity of matter

into its velocity, the common velocity of the two bodies will be but

one half of the velocity of the moving body before the stroke.

As to the second general case, where both the bodies are in motion

before the stroke, and move one and the same way. In order to find

their common velocity after impact, let the sum of their motions before

the stroke be divided by the sum of the bodies, and the quotient will

express the common velocity.

As to the third general case, where the bodies move in direct

opposition to each other, if they have equal quantities of motion, they

will upon the stroke lose all their motion, and continue at rest; for,

by the proposition, the bodies after impact will be carried with the

difference of their motions before the stroke; which difference, in

such a case, is nothing.

When two bodies meet with unequal quantities of motion, if the

difference of their motions be divided by the sum of the bodies, the

quotient will express their common velocity after the stroke; for, by

the proposition, the difference of their motions before the stroke is

equal to the sum of their motions after the stroke; consequently, that

difference divided by the sum of the bodies must give the velocity.

Such are the principal laws which govern the collision of bodies devoid

of elasticity. The motions of elastic bodies are determined by

different rules: for when they are perfectly elastic, the velocity

gained by the body struck, and the velocity lost by the striking body,

will be twice as great as if the bodies were perfectly inelastic. In

estimating, therefore, the motions of such bodies, we may first

consider what they would have been after impact, had they been

inelastic, and thence deduce the desired conclusion. See Helsham’s

Lectures, a work in which the subject appears to be very clearly

treated.

Note 27, p. 181.--DRUIDICAL REMAINS.

Karn-brêh hill rises a little to the south-west of Redruth in Cornwall,

to an elevation of 697 feet. Its principal interest is derived from the

speculations of the antiquary, Doctor Borlase, who regarded it as

having been once the grand centre of druidical worship; and he asserts,

in his Antiquities of Cornwall, that, at this very time, the remains of

those monuments which were peculiar to that priesthood may be

discovered, such as _rock-basins_, _circles_, _rock-idols_,

_cromlechs_, _karns_, _caves_, _religious enclosures_, _logan stones_,

_a gorseddau_, or place of elevation, whence the druids pronounced

their decrees, and the traces of a _grove of oaks_. This is all very

ingenious and imposing, and may be easily believed by those who have

either not visited the spot, or, having visited it, not viewed the

objects with geological eyes. There is no ground whatever for

considering the druidical monuments of Dr. Borlase as the works of man:

on the contrary, they are evidently the results of the operation of

time and the elements, the usual agents employed by Nature in the

decomposition of mountain masses: but the age of antiquarian illusion

is past; the light of geological science has dispelled the phantoms

created by the wizard Fancy, just as the rising sun dissolves the

mystic forms which the most common object assumes in twilight, when

viewed through the medium of credulity and superstition. The

“rock-basins” of antiquaries are rounded cavities on the surface of

rocks, and are occasionally as spheroidal internally as if they had

been actually formed by a turning-lathe. It was this artificial

appearance which first suggested the hypothesis concerning their

origin, and induced the antiquary to regard them as pools of

lustration. It may, however, be remarked, in the first place, that,

supposing them to have been the works of the druids, these priests must

have been indefatigable artists, for there is scarcely a block of

granite on which one or more of such pools are not visible, although

some are, undoubtedly, much more complete and imposing than others. We

shall introduce to the reader an account of these rock-basins in the

words of their great defender, and we think that he will be amused with

the ingenuity and confidence with which the antiquary dwells upon every

appearance, and bends the facts to suit his favourite theory. “Since no

author has mentioned, and attempted to explain these monuments, let us

see what light and assistance their shape and structure, exposition,

number, and place, considered together with the customs and known rites

of antiquity, may afford us in this untrodden path. Of these basins

there are two sorts; some have lips or channels to them, others have

none; and therefore, as those lips are manifestly the works of design,

not of accident, those that have so material a difference must needs

have been intended for a different use, and yet both these sorts seem

to be the works of the same people, for there is a multitude of these

basins which have no lips or outlets, as well as those which have, to

be seen on Karn-brêh hill, and elsewhere, on contiguous rocks. Their

shape is not uniform; some are quite irregular, some oval, and some are

exactly circular. Their openings do not converge in the top as a jar or

hogshead, but rather spread and widen, as if to expose the hollow as

much as possible to the skies. Some have little falls into a larger

basin, which receives their tribute, and detains it, having no outlet.

Other large ones intermixed with little ones have passages from one to

another, and, by successive falls uniting, transmit what they receive

into one common basin, which has a drain to it, that serves itself and

all the basins above it.”

“The lips do not all point in the same direction, some tending to the

south, some to the west, others to the north, and others again to the

intermediate points of the compass; _by which it seems as if the makers

had been determined in this particular, not by any mystical veneration

for one region of the heavens more than another, but by the shape and

inclination of the rock, and for the most easy and convenient outlet_.”

We must here beg the reader to pause. The above remark is really too

valuable to be suffered to pass without some notice. And so the absence

of all design and arrangement is adduced as a proof of their artificial

origin! What would Dr. Borlase have said, had all these lips been found

to point in the same direction? But to proceed:

“The size of rock-basins is as different as their shape; they are

formed from six feet to a few inches in diameter. Many uses may suggest

themselves to the imaginations of the curious from the description of

these new, and hitherto scarce-mentioned monuments; in order,

therefore, to obviate some prepossessions, and prevent the mind from

resting so far on groundless suppositions as may make it more difficult

to embrace the truth, I shall first consider what, in all probability,

_cannot_ have been the design of them.”

The doctor then proceeds to show that they could never have been

intended for evaporating salt; nor for pounding tin ore, nor for

receiving obelisks, or stone deities, nor for altars; and then suggests

that they could be no other than vessels most ingeniously contrived for

holding holy-water for the rites of washing and purification. “If,”

adds the learned antiquary, “fitness can decide the use--and where

history is deficient, it is all reason that it should--we shall not

long be at a loss. They are mostly placed above the reach of cattle,

frequently above the inspection of man; nay, the stones which have

these basins on them, do not touch the common ground, but stand on

other stones.--Wherefore? but that the water might neither be really

defiled by the former, nor incur the imaginary impurity, which touching

the ground, according to the druid opinion, gave to every thing that

was holy.” We do not know what ideas the druids entertained with

respect to the purity of water, but we have seen water in some of these

pools so impregnated with the excrement of sea-birds, that we must have

been as thirsty as Tantalus, before we could have been induced to cool

our tongues with it.

“But,” adds Dr. Borlase, “there are some basins which have no lip or

channel; and, therefore, as they could not contribute any of their

water to the common store, they _must_ have been appropriated to

another use; and since these are found in the same places with the

others above-mentioned which have outlets or mouths to them, they must

have been subservient to the same system of superstition, though in a

different method.”

“These basins are sometimes found near twenty feet high from the common

surface; and, therefore, being so withdrawn from vulgar eyes, so

elevated from the ground, which was supposed, as I said before, to

defile all, they had likely a proportionably greater degree of

reverence, and their waters accounted more holy, and more efficacious.”

We shall not trouble the reader with any further quotations from this

learned antiquary, except in concluding the history, after the fashion

of melo-dramatists, with a splendid scene, in which, with the author’s

assistance, we shall bring all the performers on the stage, dressed in

appropriate costume, and surrounded by all the pomp of druidical

worship.

“From these basins,” says Dr. Borlase, “on solemn occasions the

officiating druid, standing on an eminence, sanctified the congregation

with a more than ordinarily precious lustration before he expounded to

them, or prayed for them, or gave forth his decisions. This water he

drank, or purified his hands in, before it touched any other vessel,

and was consequently accounted more sacred than the other holy-water.

To these more private basins, during the time of libation, the priest

might have recourse, and be at liberty to judge by the quantity,

colour, motion, and other appearances in the water, of future events,

of dubious cases, without danger of contradiction from the people

below. This water might serve to mix their mistletoe withal, as a

general antidote: for, doubtless, those who would not let it touch the

ground, would not mix this their divinity (the mistletoe) with common

water. Oak leaves, without which the druid rites did scarce ever

proceed, ritually gathered and infused, might make some very medicinal

or incantorial potion. Lastly, libations of water were never to be made

to their gods, but when they consisted of this purest of all water, as

what was immediately come from the heavens, and partly therefore

thither to be returned, before it touched any other water or any other

vessel whatsoever, placed on the ground.”

“As _logan_, or rocking-stones, were some of the _piæ fraudes_ of the

druids, the basins found on them might be used to promote the juggle;

by the motion of the stone the water might be so agitated, as to delude

the enquirer by a pretended miracle; might make the criminal confess;

satisfy the credulous; bring forth the gold of the rich; and make the

injured, rich as well as poor, acquiesce in what the druid thought

proper.”

Sorry are we to destroy a web which has been so ingeniously woven by

its author; but the interests of truth admit not of compromise. Dr.

Macculloch, in an interesting paper, published in the Transactions of

the Geological Society, on the decomposition of the granite tors of

Cornwall, has justly observed, that the true nature of these

rock-basins may be easily traced by inspecting the rocks themselves. On

examination, they will always be found to contain distinct grains of

_quartz_, and fragments of the other constituent parts of the granite.

A small force is sufficient to detach from the sides of these cavities

additional fragments, showing that a process of decomposition is still

going on under favourable circumstances. The principal of these

circumstances is the presence of water, or rather the alternate action

of air and water. If a drop of water can only make an effectual

lodgement on a surface of this granite, a small cavity is sure to be

sooner or later produced; this will insensibly enlarge as it becomes

capable of holding more water; and the sides, as they continue to

waste, will necessarily retain an even and rounded cavity, on account

of the uniform texture of the rock. This explanation is sufficiently

satisfactory: in addition to which, it may be stated, that these very

basins not unfrequently occur on the perpendicular sides of rocks, as

may be distinctly seen in the granite of Scilly, and in the gritstone

rocks in the park of the late Sir Joseph Banks, in the parish of

Ashover, in Derbyshire; a fact which at once excludes the idea of their

artificial origin.

The other grotesque and whimsical appearances of rocky masses, such as

_rock idols_, _logan stones_, _&c._ are to be explained by the tendency

which granite possesses of wearing more rapidly on the angles and edges

than on the sides; thus, then, upon simple and philosophical

principles, are such appearances to be satisfactorily accounted for,

and the _phantasmagoria_ of Borlase vanishes as the light penetrates

the theatre so long dedicated to its exhibition.

We shall conclude this note with a few observations upon the celebrated

logan, or logging, stone, near the Land’s End, Cornwall, of which we

present our readers with a faithful sketch.

[Illustration: Mound of stone with a boulder balanced atop a point in

the middle.]

The foundation of this part of the coast is a stupendous group of

granite rocks, which rise in pyramidal clusters to a great altitude,

and overhang the sea. The celebrated _logan stone_ here represented is

an immense block weighing above sixty tons. The surface in contact with

the under rock is of very small extent, and the whole mass is so nicely

balanced, that, notwithstanding its magnitude, the strength of a single

man applied to its under edge is sufficient to make it oscillate. It is

the nature of granite to disintegrate into rhomboidal and tabular

masses, which, by the further operation of air and moisture, gradually

lose their solid angles, and approach the spheroidal form. The fact of

the upper part of the cliff being more exposed to atmospheric agency

than the parts beneath, will sufficiently explain why these rounded

masses so frequently rest on blocks which still preserve the tabular

form; and since such spheroidal blocks must obviously rest in that

position in which their lesser axes are perpendicular to the horizon,

it is equally evident that, whenever an adequate force is applied, they

must vibrate on their point of support.

Although we are thus led to deny the druidical origin of this stone,

for which so many zealous antiquaries have contended, still we by no

means intend to deny that the druids employed it as an engine of

superstition; it is possible that, having observed so curious a

property, they dexterously contrived to make it answer the purposes of

an ordeal, and, by regarding it as the _touch-stone_ of truth,

acquitted or condemned the accused by its motions. Mason poetically

alludes to this supposed property in the following lines:--

“Behold yon huge

And unknown sphere of living adamant,

Which, poised by magic, rests its central weight

On yonder pointed rock; firm as it seems,

Such is its strange and virtuous property,

It moves obsequious to the gentlest touch

Of him whose heart is pure, but to a traitor,

Tho’ e’en a giant’s prowess nerved his arm,

It stands as fixed as Snowdon.”

Note 28, p. 186.--ANIMAL SUCTION.

We are indebted to Sir Everard Home for a description of that peculiar

structure by which several species of animals are enabled to sustain

their bodies in opposition to the force of gravity. His first paper

upon this subject is published in the 106th volume of the Philosophical

Transactions, in which he says, he was not aware that any animal,

larger than the house-fly, was endowed by nature with such a power, so

as to admit of examination, until Sir Joseph Banks mentioned that the

_lacerta gecko_, a species of lizard, which is a native of the island

of Java, comes out of an evening from the roofs of the houses, and

walks down the smooth, hard, and polished chinam walls, in search of

the flies which settle upon them, and which are its natural food, and

then runs up again to the roof of the house. Sir Joseph, while at

Batavia, amused himself with catching this animal, by standing close to

the wall, at some distance from the lizard, with a long flattened pole,

which being made suddenly to scrape the surface of the wall, knocked

the animal down. He presented Sir Everard with a specimen weighing five

ounces and three quarters, avoirdupois, which enabled him to ascertain

the peculiar mechanism by which the feet of this animal can keep their

hold of a smooth, hard, perpendicular wall, and carry up so large a

weight as that of its body.

The foot has five toes, at the end of each of which, except that of the

thumb, is a very sharp and much curved claw; on the under surface of

each toe are sixteen transverse slits, leading to so many cavities or

pockets, the depth of which is nearly equal to the length of the slit

that forms the orifice; they all open forward, and the external edge of

each opening is serrated, like the teeth of a small-toothed comb. The

cavities, or pockets, are lined with a cuticle, and the serrated edges

are also covered with it. The structure just described is supplied with

various muscles, whose action is to draw down the claw, open the

orifices of the pockets, and turn down the serrated edges upon the

surface on which the animal stands. Upon examining attentively the

under surface of the toes, when the pockets are closed, Sir Everard

Home was struck with their resemblance to the surfaces of that portion

of the _Echineis remora_, or sucking fish, by which it attaches itself

to the shark, or to the bottom of ships; and it consequently suggested

the probability of obtaining, from an examination of this latter

apparatus, much useful information which might be applicable to the

subject of the lizard, more especially as the parts of which it is

composed are so much larger, and therefore more within the reach of

anatomical examination.

The surface on the top of the head of this fish, fitted for adhesion,

is of an oval form, and bears a considerable proportion to the size of

the whole animal; it is surrounded by a broad, loose, movable edge,

capable of applying itself closely to the surface on which it is

placed; and it is evident that when the external edge is so applied,

and the cartilaginous plates are raised up, the interstices must become

so many vacua, and the serrated edge of each plate will keep a

sufficient hold of the substance on which it rests to retain it in that

position, assisted by the pressure of the surrounding water, without a

continuance of muscular exertion. It thus appears that the adhesion of

the _sucking fish_ is produced by so many vacua being formed through an

apparatus worked by the voluntary muscles of the animal, and the

pressure of the surrounding water.

From the similarity of the mechanism of the under surface of the toes

of the _lacerta gecko_, there can be no doubt that the purpose to which

it is applied is the same: but as in the one case the adhesion is to

take place under water, and is to continue for longer periods, the

means are more simple; in the other, where the mechanism is to be

employed in air, under greater disadvantages with respect to gravity,

and is to last for very short periods, and then immediately afterwards

to be renewed, a more delicate structure of parts, a greater

proportional depth of cavities, and more complex muscular structure,

become necessary.

Having ascertained the principle on which an animal of so large a size

as the _lacerta gecko_ is enabled to support itself in its progressive

motion against gravity, Sir E. Home felt himself more competent to

inquire into the mechanism by which the common fly is enabled, with so

much facility, to support itself in still more disadvantageous

situations. In the natural size the feet of the fly are so small, that

nothing can be determined respecting them; Keller was the first person

who made a drawing of the fly’s foot in a highly magnified state, in

which the concave surfaces are visible, and which, no doubt, like those

of the lizard above described, are employed to form vacua, which enable

the fly to move under such disadvantageous circumstances. Mr. Bauer,

who has so greatly distinguished himself in microscopic researches, was

judiciously enlisted into the service of Sir E. Home upon this

occasion; and he has shown that this principle, on which progressive

motion against gravity depends, is very extensively employed by nature

in the structure of the feet of insects; and Sir Everard observes,

that, now this structure is known, it can be readily demonstrated by

looking at the movement of the feet of any insect upon the inside of a

glass tumbler, through a common magnifying glass; the different suckers

are readily seen separately to be pulled off from the surface of the

glass, and reapplied to another part.

In consequence of the expedition to the polar regions, Sir E. Home was

enabled to obtain and examine the foot of the walrus, in which he

detected a resemblance in structure to that of the fly; and it is not a

little curious that two animals so different in size should have feet

so similar in their use. In the fly the parts require to be magnified

one hundred times to render the structure distinctly visible; and in

the walrus the parts are so large, as to require being reduced four

diameters, to bring them within the size of a quarto page.

Nor is progressive motion, the only function in which Nature avails

herself of the pressure of the atmosphere for the accomplishment of her

purposes. The act of feeding is continually effected in this manner.

The operation of sucking is too familiar to require comment. It may

not, perhaps, be so generally known, that it is by the very same

process that bees reach the fine dust and juices of hollow flowers,

like the honeysuckle, and some species of foxglove, which are too

narrow to admit them. They fill up the mouth of the flower with their

bodies, and suck out the air, or at least a large portion of it, by

which the soft sides of the flower are made to collapse, and the juice

and dust are squeezed towards the insect, as completely as if the hand

had pressed it externally. It is by a similar process that the oyster

is enabled to close its shell so firmly; for, if a hole be bored in it,

it may be opened without the least difficulty.

Note 29, p. 191.--ACCIDENTAL DISCOVERIES.

Those who are not acquainted with the operations by which the mind is

enabled to arrive at truth, are too apt to attribute to accident that

which is the result of great intellectual labour and acuteness.

Observation, analogy, and experiment are the three great

stepping-stones by which the philosopher is enabled to ascend from

darkness to light: it is true that his foot may accidentally be

placed upon the first, but his own efforts are required to complete

the ascent. To the mass of mankind the preliminary step is obvious,

and they at once conclude that the succeeding ones are equally easy

and simple. In this view of the subject, it was by accident that Sir

Isaac Newton discovered the laws of gravitation, for his mind was

directed to the investigation by the accidental fall of an apple from

its tree; it was by accident that Galileo discovered the isochronous

movement of the pendulum, for it was suggested by the vibration of a

chandelier: but how many persons might have witnessed the fall of an

apple, or the vibration of a chandelier, without arriving at similar

truths? It has been said that we are indebted for the important

invention in the steam-engine, termed _hand gear_, by which its

valves or cocks are worked by the machine itself, to an idle boy of

the name of Humphrey Potter, who, being employed to stop and open a

valve, saw that he could save himself the trouble of attending and

watching it, by fixing a plug upon a part of the machine which came

to the place at the proper times, in consequence of the general

movement. If this anecdote be true, what does it prove? That Humphrey

Potter might be very idle, but that he was, at the same time, very

ingenious. It was a contrivance, not the result of accident, but of

acute observation and successful experiment. Glass is said to have

been discovered by persons having accidentally kindled a fire on the

sandy shore with sea-weed, when the alkali from the ashes united with

the silex of the sand; and Pliny tells us that _minium_, or red lead,

was first recognised, in consequence of a fire that took place at the

Piræus at Athens, where some _ceruse_, which had been exposed to the

fire, had been found converted into a red substance. A thousand such

accidents might be related, were we not affording a sample rather

than a catalogue. We are endeavouring to combat a popular but

mischievous error; and we are happy at finding the same feeling

expressed in a work which, from its extensive circulation, must prove

highly useful in correcting it. “Very few discoveries,” says the

author, “have been made by chance and by ignorant persons; much fewer

than is generally supposed. They are generally made by persons of

competent knowledge, and who are in search of them. The improvement

of the steam-engine by Watt resulted from the most learned

investigation of mathematical, mechanical, and chemical truths.

Arkwright devoted many years, five at least, to his invention of

spinning-jennies. The new process of refining sugar, by which more

money has been made in a shorter time, and with less risk and

trouble, than was perhaps ever gained by an invention, was discovered

by Mr. Howard, a most accomplished chemist, and it was the fruit of a

long course of experiments, in the progress of which, known

philosophical principles were constantly applied, and one or two new

principles ascertained.”--_Library of Useful Knowledge._

Note 30, p. 193.--WEIGHT OF THE SUPERINCUMBENT OCEAN.

If we include the pressure of the atmosphere, a body at the depth of

100 feet would sustain that of 60 pounds on the square inch; while one

at 4,000 feet, a depth by no means considerable, it would be exposed to

a pressure of about 1,830 pounds. We need not, therefore, feel

surprised, that on the foundering of a ship at sea, though its timbers

part, not a spar floats to the surface; for if the hull has sunk to a

great depth, all that is porous is penetrated with water or greatly

compressed. Captain Scoresby states that when, by the entangling of the

line of the harpoon, a boat was carried down with the whale, it

required after it was recovered two boats to keep it at the surface.

Sir J. Herschel has recorded a melancholy anecdote, which may well be

adduced in farther illustration of our subject:--“After the invention

of the diving-bell, and its success in sub-aqueous processes, it was

considered highly desirable to devise some means of remaining for any

length of time under water, and rising at pleasure without any

assistance. Some years ago an ingenious individual proposed a project

by which this end was to be accomplished. It consisted in sinking the

hull of a ship made quite water-tight, with the decks and sides

strongly supported by shores, and the only entry secured by a stout

trap-door, in such a manner, that by disengaging from within the

weights employed to sink it, it might rise of itself to the surface. To

render the trial more satisfactory, the projector himself made the

first essay. It was agreed that he should sink in twenty fathoms water,

and rise again without assistance at the expiration of twenty-four

hours. Accordingly, making all secure, and provided with the means of

making signals to indicate his situation, this unhappy victim of his

own ingenuity entered and was sunk. No signal was made, and the time

appointed elapsed. The pressure of the water at so great a depth had,

no doubt, been completely under-estimated, and the sides of the vessel

being at once crushed in, the unfortunate projector perished, before he

could even make the signal concerted to indicate his distress.”

Note 31, p. 199.

Hence _pecunia_ from pecus. _Opes_ quasi Oves. See Note 6.

Note 32, p. 207.--THE CAUSE OF IRIDESCENCE.

If a soap-bubble be blown up, and set under a glass, so that the motion

of the air may not affect it, as the water glides down the sides and

the top grows thinner, several colours will successively appear at the

top, and spread themselves from thence in rings down the sides of the

bubble, till they vanish in the same order in which they appeared; at

last a black spot appears at the top, and spreads till the bubble

bursts. Hence it follows that the colours of a body depend in some

degree upon the thickness and density of the particles that compose it;

and that, if the density be changed, the colour will likewise be

changed. That the production of colours depends upon the nature of the

surfaces upon which light falls, is beautifully exemplified by the

iridescence of mother of pearl; and which has been satisfactorily shown

to depend upon a singular peculiarity in the structure of that

substance. On its surface, which to the unassisted eye, and even to the

touch, appears to be finely polished, there are innumerable little

lines, or _grooves_, in some places as many as two or three thousand in

the space of an inch, which, lying parallel, regularly follow each

other in all their windings; by the edges of which the rays of light

are reflected, and the continual change of colour arises from their

continual bendings. Whatever doubts might have existed upon the

subject, some late experiments of Dr. Brewster have dissipated them, by

showing that the colours which play so beautifully on the surface of

mother of pearl, may be communicated by pressure to sealing-wax and

several other substances. The discovery of this fact was in some

measure accidental; he had stuck a piece of mother of pearl on a cement

made of rosin and bees-wax, and on separating this cement he found that

it had acquired the property of exhibiting colours. Several persons who

witnessed the effect, concluded that it arose from the presence of a

thin film of the mother of pearl, which might have scaled off and

adhered to the wax: but such an explanation was at once refuted, by

plunging the wax in acid, which must have dissolved the mother of

pearl, had any been present; but the acid had no effect, and the

colours of the impression remained unimpaired. It is clear, then, that

it is the grooves, as Dr. Brewster conjectured, which occasion the

iridescence in the mother of pearl, as well as in the waxen impression.

In consequence of this curious discovery, Mr. Barton succeeded in

producing the same appearance on glass, and on different metals, by

simply cutting grooved lines on their surface. These lines are so fine

that, without a microscope, they are scarcely visible, and the glass

and the metal appear to retain their polish: yet they and the colours

also may be communicated by an impression, like those from the mother

of pearl, to the wax. In like manner the varying and delicate hues

exhibited by the wings of certain butterflies, arise from the action of

light upon the parallel and equidistant striæ upon their surfaces.

Note 33, p. 224.--VEGETABLE BAROMETERS.

The following are a few of those plants which indicate changes in the

weather:--

_Chickweed_ is an excellent barometer. When the flower expands fully,

we are not to expect rain for several hours; should it continue in that

state, no rain will disturb the summer’s day. When it half conceals its

miniature flower, the day is generally showery; but, if it entirely

shuts up, or veils the white flower with its green mantle, let the

traveller take the hint and put on his great-coat. The different

species of _trefoil_ always contract their leaves at the approach of a

storm; so certainly does this take place, that these plants have

acquired the name of the _husbandman’s barometer_.

The tulip and several of the compound yellow flowers also close before

rain. There is, besides, a species of wood-sorrel, which doubles its

leaves before storms and tempests. The _bauhinia_, or mountain ebony,

_cassia_, and sensitive plants, observe the same habit.

Note 34, p. 225.--SAINT SWITHIN.

The popular adage of _Forty days’ rain after St. Swithin_, is a

tradition which seems to have derived its origin from the following

circumstance. Swithin, or _Swithum_, bishop of Winchester, who died in

868, desired that he might be buried in the open church-yard, and not

in the chancel of the minster, as was usual with other bishops; and his

request was complied with; but the monks, on his being canonized,

considering it disgraceful for the saint to lie in a public cemetery,

resolved to remove the body into the choir, which was to have been done

with solemn procession on the 15th of July. It rained, however, so

violently for forty days together at this season, that the design was

abandoned. “Now, without entering into the case of the bishop,” says

Mr. Howard, in his work on the Climate of London, “who was probably a

man of sense, and wished to set the example of a more wholesome, as

well as a more humble, mode of resigning the perishable clay to the

destructive elements, I may observe, that the fact of the hindrance of

the ceremony by the cause related is sufficiently authenticated by

tradition; and the tradition is so far valuable, as it proves that the

summers in this southern part of our island, were subject, a thousand

years ago, to occasional heavy rains, in the same way as at present.”

Mr. Howard has shown, by a table, that the notion commonly entertained

on this subject, if put strictly to the test of experience, at any one

station, in this part of the island, will be found fallacious; he,

however, very justly observes, that “the opinion of the people on

subjects connected with Natural History is commonly founded, in some

degree, on fact or experience;” and to do justice to the popular

observation in question, he states that, “in a majority of our summers,

a showery period, which, with some latitude as to time and local

circumstances, may be admitted to constitute daily rain for forty days,

does come on about the time indicated by this tradition; not that any

long space before is often so dry as to mark distinctly its

commencement.”

Note 35, p. 230.--THE WHALE.

Did the whale know his own power, he would easily destroy all the

machinery which the art of man could devise for catching him; it would

be only necessary for him to swim on the surface in a straight line in

order to break the thickest rope; but the fish, on being struck by the

harpoon, obeys a natural instinct, which, in this instance, betrays him

to his death. Sir H. Davy, in his Salmonia, observes, that the whale,

not having an air-bladder, can sink to the lowest depths of the ocean,

and mistaking the harpoon for the teeth of a sword-fish, or a shark, he

instantly descends, this being his manner of freeing himself from these

enemies, who cannot bear the pressure of a deep ocean; and from

ascending and descending in small space, he thus puts himself in the

power of the whaler.--_See Note 30._

Note 36, p. 235.--PROGRESSIVE MOTION IN FISHES:

BOATS IMPELLED BY PADDLING, ROWING, &C.

To render the subject to which this note refers farther intelligible,

we may show the means by which a fish moves forward in the water. The

accompanying diagram and demonstration are from Dr. Roget’s Bridgewater

Treatise.

[Illustration: Diagram of fish’s motion.]

The tail is the principal instrument by which the progressive motion is

effected. Thus--suppose that the tail is inclined to the right; if, in

this situation, the muscles of the left side, tending to bring the tail

in a right line with the body, are suddenly thrown into action, the

resistance of the water, by reacting against the broad surface of the

tail in the direction P R, perpendicularly to that surface, will cause

the muscular action to give the whole body an impulse in that

direction; and the centre of gravity, C, will move onwards in the

direction C B, parallel to P R. This impulse is not destroyed by the

farther flexion of the tail towards the left side, because the

principal force exerted by the muscles has already been expended in the

motion from R to M, in bringing it to a straight line with the body;

and the force which carries it on to L is much weaker, and therefore

occasions a more feeble reaction. When the tail has arrived at the

position L, indicated by the dotted outline, a similar action of the

muscles on the right side will create a resistance and an impulse in

the direction of K L, and a motion of the whole body in the same

direction, C A. These impulses being repeated in quick succession, the

fish moves forward in the diagonal C D, intermediate between the

direction of the two forces.

Upon the same principle a boat is impelled by paddling; and the action

of the rudder of a ship in turning the vessel will be readily

understood. In this latter case, however, there is an additional

mechanical advantage; since the point round which the vessel turns, is

beyond the middle and towards the prow, and hence the force applied at

the extremity of the keel acts as by an arm of a lever.

Note 37, p. 236.--FLIGHT OF BIRDS.

In appreciating the mechanical means by which a bird is enabled to

direct its course, we must not omit to take into account the power it

possesses of changing the position of the centre of gravity of its

body, so that the reaction of the air may be modified with regard to

each wing.

Note 38, p. 236.--FLIGHT OF INSECTS.

The command possessed by insects in directing and changing their

course, seems more perfect even than that of birds. Many of them travel

on their wings to immense distances, and, considering their comparative

size, they generally move through the air with greater velocity than

that of birds. Bees have been known to fly great distances from their

hive, in search of food; and the silk-worm moth has travelled more than

a hundred miles in a very short space of time. Many of our readers

have, no doubt, noticed with surprise the apparent facility with which

gnats have accompanied them, although they may have been advancing on

horseback at a full gallop; and the author during the last summer has

been forcibly struck with the manner in which flies and other insects

have kept up with a railway carriage, alternately flying in and out of

the vehicles, as though they had been at perfect rest. Some species

possess a remarkable power of poising themselves in the air, and

hovering for a length of time over the same spot, without falling or

rising, advancing or retreating; the _Dragon-fly_ affords a striking

example of this fact.

Note 39, p. 237.--OBLIQUITY OF THE WINGS OF BIRDS.

In consequence of the manner in which the wings are affixed to the

scapula, they give a stroke to the air in a direction both downwards

and backwards; so that while the former supports the bird, the latter

impels it forward. It is curious to notice that the degree of this

obliquity varies in different birds, and is evidently adapted to their

habits: thus, for instance, birds of prey have a great obliquity of

wing, which better enables them to pursue their victims in a horizontal

course; while those birds which soar to a considerable elevation, in a

nearly vertical direction, as the _Lark_, have scarcely any obliquity

of wing, but strike directly downwards.

Note 40, p. 238.--A MECHANICAL PROPOSITION.

This fact may be demonstrated by converting the triangle into a

parallelogram, of which one of the sides of the triangle will become

its diagonal: the other two sides will, of course, represent two forces

equivalent to such diagonal, which, acting in opposition to it, must

produce a balance.

Note 41, p. 241.--KITE MESSENGERS.

The curious experiments of Mr. Faraday upon the optical effects

produced by the revolutions of different wheels, might be exhibited by

arrangements adjusted as messengers.

Note 42, p. 246.--WINDS AND STORMS.

The sea and land breezes which occur in the islands of the torrid zone,

very strikingly illustrate the position laid down in the text, and

afford a good explanation of the manner in which winds may be

occasioned by a change of temperature in the air. In these, during the

hottest part of the day, the wind sets in from all quarters, and

appears to be blowing towards the centre of the island, while in the

night it changes its direction, and blows from the centre of the land

towards the sea; for since the sun’s rays produce much more heat by

their reflection from land than they do from water, that portion of air

which is over the land will soon become heated, and will ascend; a

rarefaction and diminution of the quantity of air over the central part

of the land will be thus occasioned, which must be supplied from the

sides; but, as the land cools again during the night, that portion of

air which had been previously heaped up will begin to descend, and by

spreading and equalizing itself will produce a breeze blowing from the

centre.

The _trade-winds_, so called from the advantage which their certainty

affords to trading vessels, are another example of the same kind; they

are generally stated to blow from east to west over the equator, and

are occasioned by the rarefaction of the air by the sun’s heat, and the

motion of the earth from west to east. While writing the present note,

we have seen an essay upon the subject by Captain Basil Hall, published

in an appendix to Mr. Daniel’s admirable work on Meteorology: the

perusal of this paper has induced us to cancel what we had written, and

to refer the reader to the essay itself; for it is quite impossible to

do justice to the views it entertains, in the limited space necessarily

prescribed to us in this note.

On the coast of Guinea, the wind always sets in upon the land, blowing

westerly instead of easterly; this exception arises from the deserts of

Africa, which lie near the equator, and being a very sandy soil,

reflect a great degree of heat into the air above them, which being

thus rendered lighter than that which is over the sea, the wind

continually rushes in upon the land to restore the equilibrium.

Among the irregular winds, or those which are not constant, but

accidental, may be noticed the _whirlwind_, the _harmattan_, and the

_sirocco_. The first of these is occasioned by the meeting of two or

more currents of wind from opposite directions, and which can only be

occasioned by some temporary but violent disturbance of equilibrium.

The _harmattan_ is met with on the western coast of Africa, and is

generally attended by great heat and fog; it appears to be occasioned

by a conflict between the heated sands of Africa, and the regular

direction of the trade-winds over that continent, and, by disturbing

their progress, it is frequently the forerunner of a hurricane in the

West Indies. The _sirocco_ occurs in Egypt, the Mediterranean, and in

Greece, and is chiefly characterised by its unhealthy qualities. The

air, by passing over the heated sands of Egypt, becomes so dried and

rarefied as to be scarcely fit for respiration, and, being thus

prepared, it absorbs so much humidity on passing the Mediterranean as

to form a suffocating and oppressive kind of fog.

Mr. Daniel observes, that the currents of a heated room, in some

measure, exemplify the great currents of the atmosphere. If the door be

opened, the flame of a candle held to the upper part will show, by its

inclination, a current flowing outwards; but, if held near the floor,

it will be directed inwards. If the door be closed suddenly from

without, it moves with the in-coming current, and against the

out-going, and a condensation of air takes place in the room; which is

proved by the rattling of the windows, and the bursting open of any

door in the room, if slightly closed. If the door close from within, it

moves against the in-coming current, and with the out-going, and a

rarefaction of the air in the room takes place; which is evidenced by

the rattling of the windows, and the bursting open of another door in

the contrary direction.

Meteorology has been long considered the least perfect branch of

natural knowledge; so apparently capricious and irregular are its

phenomena, that philosophers had almost abandoned the idea of bringing

them under the operation of any general laws. Brighter lights are,

however, now dawning upon us. Mr. Whewell, in his Bridgewater Treatise,

has explained the manner in which the various currents of the

atmosphere maintain a necessary balance in the distribution of heat and

moisture around the globe, and has thus reduced to order and design

phenomena which have hitherto been regarded as unconnected and

fortuitous. Lieut.-Col. Reid, by his late happy investigation of the

law of storms, will, no doubt, lead us into a novel path of the most

important discoveries. He has satisfactorily proved, by a mass of

evidence derived from numerous logbooks, that storms obey fixed laws.

His attention was ardently directed to the subject by having been at

Barbadoes immediately after the great hurricane of 1831, which in the

short space of seven hours killed upwards of 1400 persons on that

island alone. The discoveries of Col. Reid may be thus briefly

stated.--That hurricanes are whirlwinds of great diameter, always

revolving according to an invariable law, viz. from right to left

(supposing yourself standing in the centre), or in the opposite way to

the hands of a watch, in the northern hemisphere, and in a contrary

direction in southern latitudes; at the same time they have a

progressive motion in a curved line, and as they advance their

diameters appear to enlarge and their violence to diminish; it has been

also found that in the centre of the vortex there is a lull, or calm.

Col. Reid observes that the simplest mode of illustrating the subject

is to cut out concentric circles, so as to represent progressive

whirlwinds, by moving which over any tract, the veering of the wind

will be easily understood. The reader may form a more familiar idea by

causing the water to circulate in a basin, which will represent the

violent circular motion of the storm-wind, with a calm in the centre of

the vortex. Suppose this to be also moving onward at a rate of about

seven miles an hour, and he will have a correct notion of the subject.

Since the storms expand in size and diminish in force as they proceed

towards the poles, and the meridians at the same time approach each

other, gales become huddled together; and hence, apparently, the true

cause of the very complicated nature of the winds in our latitude.

Observations would also appear to render it probable that there exists

an accordance of the force of storms with the law of magnetic

intensity; for example, it is at its minimum at St. Helena, where

storms never occur; on the contrary, the lines of greatest intensity

seem to correspond with the latitudes of typhoons and hurricanes. To

what important discoveries may not the pursuit of this enquiry lead us?

The practical importance of the foregoing facts must be obvious: to use

the expression of Sir John Herschel, “they will teach seamen how to

steer their ships, and save thousands of lives.” They will thus learn

on which side to lay-to a ship in a storm, for, by watching the veering

of the wind, they will ascertain the direction in which it is falling;

if violent, and the changes sudden, the ship will probably be near the

centre of the vortex; whereas, if the wind blows a great length of time

from the same point, and the changes are gradual, it may reasonably be

supposed the ship is near the extremity of it. The barometer also

becomes a very important instrument upon these occasions; the rapid

rotatory motion of a column of the atmosphere necessarily occasions its

fall, and this fall is always greatest at the centre of the storm. When

it begins to rise, the centre has passed, and when the wind has

sufficiently abated to enable a ship to make sail, she may then bear

away with safety; but near the middle of the hurricane, before the

barometer begins to rise, all square-sails must be dangerous.

Note 43, p. 250.--ANCIENT ARCHERY.

We are reminded, upon this occasion, of part of a stanza in the

well-known ballad of Chevy Chace, where an English archer aimed his

arrow at Sir Hugh Montgomery:--

“The _grey goose wing_ that was thereon,

In his hearte’s blood was wett.”

The more ancient ballad, however, reads _swane-feathers_. In the “Geste

of Robyn Hode,” among Mr. Garrick’s old plays, in the Museum, the

arrows of the outlaw and his companions are particularly described:--

“With them they had an hundred bowes,

The strings were well ydight;

An hundred shefe of arrows good,

With hedes burnish’d full bryght;

And every arrowe an ell longe,

With _peacocke_ well ydight,

And rocked they were with white silk,

It was a semely sight.”

And Chaucer, in the description of the squyer’s yeoman, says:--

“And he was clad in cote and hode of greene;

A sheafe of _peacocke_ arrows bryght and shene,

Under his belt he bare full thriftely,

Well coude he dresse his tackle yemanly:

His arrowes drouped not with fethers lowe,

And in his hand he bare a mighty bowe.”

_Prol. to Cant. Tales._

In order to show the dandyism displayed by the archers of former times,

it may be stated, that, in the wardrobe accounts of the 28 Edw. I. p.

359, is a charge for verdigrise to stain the feathers of the arrows

green. A wardrobe account of the 4 Edw. II. furnishes an entry for

peacock arrows, “Pro duodecim flecchiis cum pennis de _pavone_, emptis

pro rege de 12 den.”

As this note has some connexion with the shuttlecock,[84] as well as

the arrow, we may take this opportunity of introducing a passage, which

was accidentally omitted in the text; it refers to the method of

playing this game at Turon, in Cochin China; and which is described by

a traveller as follows:--“Instead of using a battledoor,[85] as is the

custom in England, the players stood seven or eight in a circle; and

after running a short race, and springing from the floor, they met the

descending shuttlecock with the sole of the foot, and drove it up again

with force high in the air. The game was kept up with much animation,

and seldom did the players miss their stroke, or give it a wrong

direction. The shuttlecock was made of a piece of dried skin rolled

round, and bound with strings. Into this skin were inserted three

feathers, spreading out at top, but so near to each other, where they

were stuck into the skin, as to pass through the holes, little more

than a quarter of an inch square, which were always made in the centre

of Cochin copper coins. We made one or two awkward attempts at the

game, not only to our own confusion, but much to the amusement of the

natives. It must, however, be remembered, that, amongst these ingenious

people, the feet assist, as auxiliaries to the hands, in the exercise

of many trades, particularly that of boat-building.”

-----

Footnote 84:

Shuttlecock, more correctly, perhaps, shuttle-_cork_, although

Skinner thinks it is called a _cock_ from its feathers.

Footnote 85:

So called from door, taken for a flat board; and battle, for

striking, _i. e._ a striking-board.

-----

Note 44, p. 270.--SOUND CONVEYED BY SOLID BODIES.

A beautiful experiment was lately instituted at Paris, to illustrate

this fact, by Biot. At the extremity of a cylindrical tube, upwards of

3000 feet in length, a ring of metal was placed, of the same diameter

as the aperture of the tube; and in the centre of this ring, in the

mouth of the tube, was suspended a clock-bell and hammer. The hammer

was made to strike the ring and the bell at the same instant, so that

the sound of the ring would be transmitted to the remote end of the

tube through the conducting power of the matter of the tube itself;

while the sound of the bell would be transmitted through the medium of

the air included within the tube. The ear being then placed at the

remote end of the tube, the sound of the ring, transmitted by the metal

of the tube, was first distinctly heard; and, after a short interval

had elapsed, the sound of the bell, transmitted by the air in the tube,

was heard. The result of several experiments was, that the metal of the

tube conducted the sound with about ten and a half times the velocity

with which it was conducted by the air; that is, at the rate of about

11,865 feet per second.

Note 45, p. 288.--EXPRESSIVE MUSIC.

The biographer of Josquin des Prez, the celebrated musician, and

_maestro di capella_ to Louis XII. King of France, relates an anecdote

which may be here told in connexion with the present subject. When

Josquin was first admitted into the service of the French monarch, he

had been promised a benefice by his Majesty; but this Prince, contrary

to his usual habits, for he was in general both just and liberal,

forgot the promise he had made; when Josquin, after suffering great

inconvenience from the shortness of his Majesty’s memory, ventured by

the following expedient to remind him publicly of his promise without

giving offence. He had been commanded to compose a motet for the Chapel

Royal, on which occasion he selected part of the 119th Psalm, “_Memor

esto verbi tui servo tuo_”--“_Oh think of thy servant, as concerning

thy word_,” which he set in so supplicating and exquisite a manner,

that it was universally admired, particularly by the King, who was not

only touched by the music, but felt the words so effectually, that he

soon afterwards granted his petition, by conferring on him the promised

preferment. For which act of justice and munificence, Josquin, with

equal felicity, composed as a hymn of gratitude another part of the

same Psalm,--“_Bonitatem fecisti cum servo tuo, Domine_”--“_Oh Lord,

thou has dealt graciously with thy servant._”

Josquin, among musicians, was the giant of his time, and seems to have

arrived at universal monarchy and dominion over the affections and

passions of the musical part of mankind; indeed, his compositions were

as well known and as much practised throughout Europe at the beginning

of the sixteenth century, as those of Handel were in Europe sixty years

ago.

Note 46, p. 294.--IMAGINARY FORMS.

The following case, quoted by Sir David Brewster, in his work on

“Natural Magic,” from the life of Peter Heaman, a Swede, who was

executed for piracy and murder at Leith in 1822, will afford a very

curious example of the influence of the imagination in creating

distinct forms out of an irregularly shaded surface. “One remarkable

thing was, one day as we mended a sail, it being a very thin one, after

laying it upon deck in folds, I took the tar-brush and tarred it over

in the places which I thought needed to be strengthened. But when we

hoisted it up, I was astonished to see that the tar I had put upon it

represented a gallows and a man under it without a head. The head was

lying beside him. He was complete, body, thighs, legs, arms, and in

every shape like a man. Now, I oftentimes made remarks upon it, and

repeated them to the others. I always said to them all, ‘You may depend

upon it that something will happen.’ I afterwards took down the sail on

a calm day, and sewed a piece of canvass over the figure to cover it,

for I could not bear to have it always before my eyes.”

The curious effect of chance resemblance was particularly remarked by

Leonardo da Vinci in the moss and stains on old stones. And, in our own

times, this faculty of the imagination has not unfrequently been

enlisted into the service of the fortune-teller for purposes of fraud

and imposition. The following story is related on credible testimony.

“A British officer, in expectation of promotion, and of being united to

a lady in marriage, sought a gipsy fortune-teller. The sorceress, no

doubt, had made herself well acquainted with these circumstances. On

entering the room, she ordered a large glass of spring-water, into

which she poured the white of a newly-laid egg. After shaking the

mixture for some time, she so far succeeded as to induce the credulous

observer to declare that he saw most distinctly the image of the ship

in which he was to hoist his flag, the church in which he was to be

married, and his bride going with him into the church.”--_The Gipsies’

Advocate_, by J. Crabb.

Note 47, p. 295.--FAIRY RINGS.

Dr. Wollaston, in a paper published in the Philosophical Transactions,

(1807, p. 133,) relates some interesting observations he made on the

progressive changes of these rings, and which satisfactorily explain

their origin. He observed, that some species of fungi were always to be

found at the exterior margin of the dark ring of grass if examined at

the proper season. The position of the fungi led him to believe, that

progressive increase from a central point was the probable mode of

formation of the ring; and he thought it likely that the soil which had

once contributed to the support of fungi, might be so exhausted as to

be rendered incapable of producing a second crop. The defect of

nutriment on one side would occasion the new roots to extend themselves

solely in the opposite direction, and would cause the circle of fungi

continually to proceed, by annual enlargement, from the centre

outwards. The luxuriance of the grass follows as a natural consequence,

as the soil of an interior circle is enriched by the decayed roots of

fungi of the succeeding year’s growth. During the growth of fungi, they

so entirely absorb all nutriment from the soil beneath, that the

herbage is often for a while destroyed, and a ring appears bare of

grass, surrounding the dark ring; but, after the fungi have ceased to

appear, the soil where they had grown becomes darker, and the grass

soon vegetates again with peculiar vigour. Dr. Wollaston had many

opportunities of remarking, that, when two circles interfere with each

other’s progress, they do not cross each other, but are invariably

obliterated between the points of contact. The exhaustion occasioned by

each obstructs the progress of the other, and both are _starved_; a

circumstance which affords a strong confirmation of the above theory.

Note 48, p. 300.--RESONANCE.

In order to comprehend the nature of _reciprocated vibration_, or

_resonance_, let the reader keep in his remembrance the analogy between

musical vibration, and the oscillation of the pendulum, as explained at

page 275. If he well understands the phenomena of the latter, he will

readily comprehend those of the former. Galileo observed that a heavy

pendulum might be put in motion by the least breath of the mouth,

_provided the blasts were often repeated, and made to keep time exactly

with the vibrations of the pendulum_: from the same sympathetic

communication of vibrations will two pendulum clocks fixed to the same

wall, or two watches lying upon the same table, take the same rate of

going, though they would not agree with one another if placed in

separate apartments. Mr. Ellicot indeed observed that the pendulum of

one clock was even able to stop that of the other; and that the stopped

pendulum, after a certain time, would resume its vibrations, and in its

turn stop the vibrations of the other. We have here a correct

explanation of the phenomena of _Resonance_; for the undulations

excited by a vibratory body are themselves capable of putting in motion

all bodies whose pulses are coincident with their own, and consequently

with those of the primitive sounding body; hence the vibrations of a

string, when another, tuned in unison with it, is made to vibrate.

Upon the same principle does the resonance, or reciprocated vibrations

of columns of air, depend. We are much indebted to Mr. Wheatstone for

our knowledge of this branch of acoustics; he has shown that, if a

tuning-fork or a bell be sounded before a tube inclosing a column of

air of the necessary length, the original sound will be augmented by

the rich resonance of that air; and that the sounds of tuning-forks, if

held before the cavity of the mouth, may be reciprocated most intensely

by adjusting the alterable volume of air contained within it to the

pitch of the instrument; by placing, for instance, the tongue, &c. in

the position for the nasal continuous sound of _ng_ (in song), and then

altering the aperture of the lips, until the loudest sound was

obtained, he readily accomplished his object.

If two vibrating tuning-forks, differing in pitch, be held over a

closed tube, furnished with a moveable piston, either sound may be made

to predominate, by so altering the piston as to obtain the exact column

of air which will reciprocate the required sound. The same result may

be obtained by selecting two bottles (which may be tuned with water)

each corresponding to the sound of a different tuning fork; on bringing

both tuning-forks to the mouth of each bottle alternately, that sound

only will be heard, in each case, which is reciprocated by the

unisonant bottle; or, in other words, by that bottle which contains a

column of air susceptible of vibrating in unison with the fork.

Among the Javanese instruments brought to England by the late Sir

Stamford Raffles, there is one called the _gender_, in which the

resonances of columns of air are employed to augment, we might almost

say to render audible, the sounds of vibrating metallic plates. Under

each of these plates is placed an upright bamboo, containing a column

of air of the proper length to reciprocate the lowest sound of such

plate. If the aperture of the bamboo be covered with pasteboard, and

its corresponding plate be struck, a number of acute sounds only

(depending on the more numerous subdivisions of the plate) will be

heard; but, on removing the pasteboard, an additional deep rich tone is

produced by the resonance of the column of air within the tube.

It is only by a knowledge of this principle that the theory of the

Guimbarde, or Jew’s harp, can be well understood.

Note 49, p. 300.--THE JEW’S HARP.

The Memoires of Madame de Genlis first made known the astonishing

powers of a poor German soldier on the Jew’s harp. This musician was in

the service of Frederick the Great, and finding himself one night on

duty under the windows of the king, played the Jew’s harp with so much

skill, that Frederick, who was a great amateur of music, thought he

heard a distinct orchestra. Surprised on learning that such an effect

could be produced by a single man with two Jew’s harps, he ordered him

into his presence; the soldier refused, alleging that he could only be

relieved by his colonel; and that, if he obeyed, the king would punish

him the next day for having failed to do his duty. Being presented the

following morning to Frederick, he was heard with admiration, and

received his discharge and fifty dollars. This artist, whose name

Madame de Genlis does not mention, is called Koch; he has not any

knowledge of music, but owes his success entirely to a natural taste.

He has made his fortune by travelling about, and performing in public

and private; and is now living retired at Vienna, at the advanced age

of more than eighty years. He used two Jew’s harps at once, in the same

manner as the peasants of the Tyrol; and produced, without doubt, the

harmony of two notes struck at the same moment, which was considered by

the musically-curious as somewhat extraordinary, when the limited

powers of the instrument were remembered. It was Koch’s custom to

require that all the lights should be extinguished, in order that the

illusion produced by his playing might be increased.

It was reserved, however, for Mr. Eulenstein to acquire a musical

reputation from the Jew’s harp. After ten years of close application

and study, this young artist has attained a perfect mastery over this

untractable instrument. In giving some account of the Jew’s harp,

considered as a medium for musical sounds, we shall only present the

result of his discoveries. This little instrument, taken singly, gives

whatever grave sound you may wish to produce, as a _third_, a _fifth_,

or an _octave_. If the grave tonic is not heard in the bass Jew’s harp,

it must be attributed not to the defectiveness of the instrument, but

to the player. In examining this result, you cannot help remarking the

order and unity established by nature in harmonical bodies, which

places music in the rank of exact sciences. The Jew’s harp has three

different tones; the bass tones of the first octave bear some

resemblance to those of the flute and clarionet; those of the middle

and high to the _vox humana_ of some organs; lastly, the harmonical

sounds are exactly like those of the _harmonica_. It is conceived that

this diversity of tones affords already a great variety in the

execution, which is always looked upon as being feeble and trifling, on

account of the smallness of the instrument. It was not thought possible

to derive much pleasure from any attempt which could be made to conquer

the difficulties of so limited an instrument; because, in the extent of

these octaves, there were a number of spaces which could not be filled

up by the talent of the player; besides, the most simple modulation

became impossible. Mr. Eulenstein has remedied that inconvenience, by

joining sixteen Jew’s harps, which he tunes by placing smaller or

greater quantities of sealing-wax at the extremity of the tongue. Each

harp then sounds one of the notes of the gamut, diatonic or chromatic;

and the performer can fill all the intervals, and pass all the tones,

by changing the harp. That these mutations may not interrupt the

measure, one harp must always be kept in advance, in the same manner as

a good reader advances the eye, not upon the word which he pronounces,

but upon that which follows.

Note 50, p. 316.--VERBAL TELEGRAPH.

This project has lately been revived; in a late number of the _Revue

Encyclopédique_ there is a proposal to communicate verbal intelligence,

in a few moments, to vast distances; and this not by symbols, as in the

Telegraph, but in distinct articulate sounds uttered by the human

voice. The plan is said to have originated with an Englishman, Mr.

Dick, according to whose experiments the human voice may be made

intelligible at the distance of twenty-five or thirty miles. It has

been stated, in Note 44, that the celebrated Biot had ascertained that

sound travels more than ten times quicker when transmitted by solid

bodies, or through tubes, than when it passes through the open air; at

the distance of more than half a mile the low voice of a man was

distinctly heard. Father Kircher relates in some of his works, that the

labourers employed in the subterranean aqueducts of Rome heard each

other at the distance of several miles. The note which follows was

published in the early edition of this work, before the subject

attracted any notice, or any railroad had been completed. It is

therefore reprinted without alteration.

Note 51, p. 316.--ELECTRICAL TELEGRAPH.

It has often occurred to the author of these pages, during his

reveries, that the means of conveying intelligence with immense

rapidity may be hereafter invented by the Electrician.--Should a system

of railways be established throughout the country, it might lead to

some expedient by which such a desideratum could be accomplished

through the medium of electrical discharges. Upon this subject we have

accidentally fallen upon a curious notice in Arthur Young’s Travels in

France (vol. i. p. 65). “M. Lomond has made a very curious discovery in

electricity; you write two or three words on a paper, he takes it with

him into his room, and there turns a machine inclosed in a cylindrical

case, at the top of which is an electrometer of pith balls; by means of

a wire, a connexion is made with a similar cylinder and electrometer in

a distant apartment, and his wife, by remarking the corresponding

motions of the balls, writes down the words they indicate; from which

it appears that he has formed an _Alphabet of Motion_. As the length of

the conducting wire makes no difference in the effect, a correspondence

might be carried on at any distance, as, for example, within or without

a besieged town; or for purposes much more interesting and useful.

Whatever the uses may be, the invention is beautiful.”

Note 52, p. 368.--CARRIER PIGEONS.

The _carrier_ is a variety of the common domestic pigeon, and which,

from the superior attachment that it shows to its native place, is

employed in many countries as the most expeditious courier. The letters

are tied under its wing, it is let loose, and in a very short space

returns to the home it was brought from, with its advices. This

practice was much in vogue in the East; and at Scanderoon, till of late

years, it was used on the arrival of a ship, to give the merchants at

Aleppo a more expeditious notice than could be done by any other means.

In our own country, these aerial messengers have been employed for a

very singular purpose, having been let loose at Tyburn at the moment

the fatal cart was drawn away, to notify to distant friends the

departure of the unhappy criminal.

In the East, the use of these birds seems to have been greatly

improved, by having, if we may use the expression, relays of them ready

to spread intelligence to all parts of the country; thus it is stated

by Ariosto (canto 15), that the governor of Damiata circulated the news

of the death of Orrilo. “As soon as the commandant of Damiata heard

that Orrilo was dead, he let loose a pigeon, under whose wing he had

tied a letter. This fled to Cairo, from whence a second was despatched

to another place, as is usual; so that, in a very few hours, all Egypt

was acquainted with the death of Orrilo.”

But the simple use of them was known in very early times. Anacreon

tells us (ode ix.) that he conveyed his billet-doux to Bathyllus by a

dove.

Taurosthenes also, by means of a pigeon he had decked with purple, sent

advice to his father, who lived in the isle of Ægina, of his victory in

the olympic games, on the very day he had obtained it.[86] And, at the

siege of Modena, Hirtius without, and Brutus within the walls, kept, by

the help of pigeons, a constant correspondence; baffling every

stratagem of the besieger, Antony, to intercept their couriers. In the

times of the crusades, there are many more instances of these birds of

peace being employed in the service of war: Joinville relates one

during the crusade of _Saint Louis_, and Tasso another, during the

siege of Jerusalem.--_Pennant’s British Zoology._

The Dutch variety is the most valuable; a pair of the best kind being

worth from five to eight pounds. It is lighter than the English pigeon,

and flies nearly as fast again. It proceeds at the rate of 60 miles an

hour, and has been known to complete a journey of 800 miles, but this;

it is presumed, is not continuous, but assisted by occasional rest. The

bird learns but one lesson; it may carry from Antwerp to London, or to

any other place, but it will only pass between two such places. It

evidently travels by sight; when tossed, it circles, then rises in a

spiral, observes its route and darts off. It will not fly at night;

and, should the day be foggy, it is delayed, and sometimes lost.

Footnote 86:

_Ælian. Var. Hist._ lib. ix. c. 2. Pliny, lib. x. c. 24, says that

swallows have been made use of for the same purpose. Their rate of

flight has been estimated at a mile in a minute, for ten hours, or

600 miles per day.

Note 53, p. 371.--ORIGIN OF POPULAR CEREMONIES.

The soothsayers attributed many mystic properties to the coral; and it

was believed to be capable of giving protection against the influence

of _Evil Eyes_: it was even supposed that coral would drive away devils

and evil spirits; hence arose the custom of wearing amulets composed of

it around the neck, and of making crowns of it. Pliny and Dioscorides

are very loud in the praises of the medicinal properties of this

substance; and Paracelsus says that it should be worn round the necks

of infants, as an admirable preservative against fits, sorcery, charms,

and even against poison. It is a curious circumstance that the same

superstitious belief should exist among the negroes of the West Indies,

who affirm that the colour of coral is always affected by the state of

health of the wearer, it becoming paler in disease. In Sicily it is

also commonly worn as an amulet by persons of all ranks; as a security

against an _evil eye_, a small twisted piece, somewhat resembling a

horn, is worn at the watch-chain, under the name of _Buon Fortuna_, and

is occasionally pointed at those who are supposed to entertain evil

intention. His late Sicilian Majesty was celebrated for his faith in,

and frequent use of, the _buon fortuna_.--But to return to the coral

usually suspended around the necks of children in our own country. In

addition to the supposed virtues of the coral, it may be remarked that

silver bells are usually attached to it, which are generally regarded

as mere accompaniments to amuse the child by their jingle; but the fact

is, that they have a different origin, having been designed to frighten

away evil spirits. For the same superstitious objects were bells

introduced into our churches as a species of charm against storms and

thunder, and the assaults of Satan.

In farther illustration of the truth, that a custom has frequently

survived the tradition of its origin, it may be here observed, that the

common practice of persons who are unable to write, making their mark

or _cross_, is derived from our Saxon ancestors, who affixed the sign

of the cross, as a signature to a deed, whether they could write or

not. Several charters still remain, to which kings and persons of great

eminence affix “_Signum Crucis manu propriá pro ignorantiá literarum_.”

Hence is derived the expression of _signing_ instead of _subscribing_ a

paper. In like manner, the physician of the present day continues to

prefix to his prescriptions the letter R, which is generally supposed

to mean _Recipe_, but which, in truth, is a relict of the astrological

symbol of Jupiter, formerly used as a species of superstitious

invocation.

Note 54, p. 379.--INVENTION OF THE GAME OF CHESS.

Alphesadi, an Arabian writer, quoted by Montucla in his _Histoire des

Mathematiques_, expressly mentions the invention of chess as of

Indian origin, and relates the following very curious Indian

tradition:--Ardschir, King of the Persians, having invented the game

of _Tric-Trac_, and being exceedingly vain of it, a certain Indian,

named Sessa, the son of Daher, invented the game of chess, and

presented his chess-board and chess-men to the king of the Indies.

The sovereign was so much pleased, that he desired Sessa to name his

reward, when this man made the apparently modest request, that he

should receive as a gift so much corn as could be estimated by

beginning with one grain, and doubling as many times as there were

squares upon the chess-board, viz. 64. The king felt displeased at

having his munificence thus slighted by a request so limited and so

unworthy to be a gift from royalty; but, as Sessa remained firm,

orders were given to the chief minister that he should be satisfied:

when, however, the visir had by calculation ascertained the enormous

quantity of corn which would be required, he waited upon the king,

and with some difficulty convinced him of the fact; upon which the

king sent for Sessa,--and said to him, that he admired his powers of

calculation even more than the ingenuity of the game which he had

presented to him, and, in respect to his promise as to the corn, he

was compelled to acknowledge himself to be insolvent.

Dr. Wallis, the friend of Sir Isaac Newton, and Savilian Professor of

Oxford, found that the quantity of corn would be such as to be capable

of forming a pyramid, the measurement of which would be nine English

miles in height, and nine similar miles for each of the four sides of

the base. After this, Montucla also states some elaborate calculations

made by himself, and proves, amongst other remarkable facts, that the

quantity of corn in question would cover 162,000 square leagues to the

depth of one foot, French measure, which would be at least three times

the extent of the surface of France as it was about the year 1796, and

which he estimates at 50,000 square leagues.

Note 55, p. 388.--AN ARITHMETICAL TRICK.

This problem is to be found in Hutton’s Recreations, and is stated as

follows:--

“A person having in one hand an _even_ number of shillings, and in the

other an _odd_, to tell in which hand he has the even number.”

“Desire the person to multiply the number in the right hand by any even

number whatever, and that in the left by any odd number; then bid him

to add together the two products, and if the whole sum be odd, the even

number of shillings will be in the right hand, and the odd number in

the left; if the sum be even, the contrary will be the case. By a

similar process, a person having in one hand a piece of gold, and in

the other a piece of silver, we can tell in which hand he holds the

gold, and in which the silver. For this purpose, some value represented

by an even number, such as 8, must be assigned to the gold, and a value

represented by an odd number, such as 3, must be assigned to the

silver; after which the operation is exactly the same as in the

preceding example.

“To conceal the artifice better, it will be sufficient to ask whether

the sum of the two products can be halved without a remainder; for, in

that case, the total will be even, and in the contrary case odd.

“It will be readily seen that the pieces, instead of being in the two

hands of the same person, may be supposed to be in the hands of two

persons, one of whom has the even number, or piece of gold, and the

other the odd number, or piece of silver. The same operations may then

be performed in regard to these two persons, as are performed in regard

to the two hands of the same person, calling the one, privately, the

right, and the other the left.”

Note 56, p. 389.--AN ALGEBRAIC PROBLEM.

It is by discovering the number of counters left on the board that this

trick is performed. By means of a table the problem may be immediately

solved; but as such a reference would be inconvenient, and, indeed,

destructive to the magic of the trick, a Latin verse is substituted,

which may be easily carried in the memory, and will be found to answer

all the purposes of a table. In order, however, that the reader may

become thoroughly acquainted with the machinery of the trick, we shall

explain it in the words of its author. The problem is stated as

follows: “_Three things being privately distributed to three persons,

to guess that which each has got._”

Let the three things be a ring, a shilling, and a glove. Call the ring

A, the shilling E, and the glove I; and in your own mind distinguish

the persons by calling them first, second, and third. Then take

twenty-four counters, and give one of them to the first person, two to

the second, and three to the third. Place the remaining eighteen on the

table, and then retire, that the three persons may distribute among

themselves the three things proposed without your observing them. When

the distribution has been made, desire the person who has the ring to

take from the remaining eighteen counters as many as he has already;

the one who has the shilling to take twice as many as he has already,

and the person who has the glove to take four times as many; according

to the above supposition then, the first person has taken one, the

second four, and the third twelve; consequently, one counter only

remains on the table. When this is done, you may return, and, by the

number left, can discover what thing each person has taken, by

employing the following words:----

1 2 3 5 6 7

_Salve_ _certa_ _animæ_ _semita_ _vita_ _quies._

To make use of these words, you must recollect, that in all cases there

can remain only 1, 2, 3, 5, 6, or 7 counters, and never 4. It must

likewise be observed, that each syllable contains one of the vowels,

which we have made to represent the things proposed, and that the first

syllable of each word must be considered as representing the first

person, and the second syllable the second. This being comprehended, if

there remains only one counter, you must employ the first word, or

rather the two first syllables, _sal-ve_, the first of which, that

containing A, shows that the first person has the ring represented by

A; and the second syllable, that containing E, shows that the second

person has the shilling represented by E; from which you may easily

conclude that the third person has the glove. If two counters should

remain, you must take the second word _cer-ta_, the first syllable of

which, containing E, will show that the first person has the shilling

represented by E; and the second syllable, containing A, will indicate

that the second person has the ring represented by A. In general,

whatever number of counters remain, that word of the verse which is

pointed out by the same number must be employed.

Instead of the above Latin verse, the following French one might be

used:--

1 2 3 5 6 7

_Par fer_ _César_ _jadis_ _devint_ _si grand_ _prince._

In using the above line, it must be considered as consisting only of

six words.

This problem might be proposed in a manner somewhat different, and

might be applied to more than three persons. Those of our readers who

may be desirous of further information on the subject, must consult

Bachet in the 25th of his _Problèmes plaisantes et délectables_.

THE END.

Transcriber’s Notes

In order to get illustrations close to long descriptions and

discussions of them, a few long paragraphs have been divided in two at

logical places.

One obvious typographical error in punctuation was corrected.

All footnotes have been relocated at the ends of chapters.

Descriptive captions have been added to the text version for many

illustrations by the Transcribers and are deemed by them to be in the

public domain.