If several of these jars be united, a large quantity of electricity can

be collected; but, in arranging them, all the interior coatings must be

made to communicate by metallic rods, and a similar union must be

effected among the exterior coatings. When thus arranged, the whole

series may be charged as if they formed but one jar.

[Illustration]

For the purpose of making a direct communication between the inner or

outer coatings of a jar or battery, by which a discharge is effected, an

instrument called a discharging rod is employed. It consists of two bent

metallic rods, terminating at one end by brass balls, and connected at

another by a joint which is fixed to the end of a glass handle, and

which, acting like a pair of compasses, allows of the balls being

separated at certain distances. When opened to the proper degree, one of

the balls is made to touch the exterior coating, and the other ball is

then brought into contact with the knob of the jar, when a discharge is

effected; while the glass handle secures the person holding it from the

effects of the shock.

DANCING BALLS AND DOLLS.

[Illustration]

Get two round pieces of wood, A B, and coat them with tinfoil; or two

pieces of metal plate; attach one of them to the prime conductor by a

chain, and let it hang about two or three inches from the knob. Place

some pith-balls upon the bottom piece of wood B, and bring it under the

other. Immediately this is done, and the upper piece is charged with

electricity from the machine, the pith-balls will jump up and down, and

from one to the other with great rapidity. If some of the pith be formed

into little figures, they will also dance and leap about in the most

grotesque manner. The same may be made to dance by merely holding the

inside of a dry glass tumbler to the prime conductor for a few minutes,

while the machine is in action, and then if this be placed over them

they will jump about, to the astonishment of the spectators, as the

cause of their motions is not quite so apparent.

THE ELECTRICAL KISS.

This amusing experiment is performed by means of the electrical stool.

Let any lady challenge a gentleman not acquainted with the experiment to

favour her with a salute. The lady thereupon mounts the glass stool, and

takes hold of a chain connected with the prime conductor. The machine

being then put in motion the gentleman approaches the lady, and

immediately he attempts to imprint the seal of soft affection upon her

coral lips, a spark will fly in his face, which generally deters him

from his rash and wicked intention.

RINGING BELLS.

[Illustration]

Bells may be made to ring by electricity in the following manner. Let

three small bells be suspended from a brass wire, D D, and supported by

a glass pillar A, passing through bell B to the bell E. The electrical

apparatus being attached to the knob F, the electricity passes down the

wires D D to the bells, which are then positively electrified and

attract the clappers C C, that are negatively so, in consequence of

being insulated by the silken strings, which are not conductors. The

bells therefore attract the clappers till they are charged, when they

strike against the centre bell to discharge themselves, and thus a peal

is rung on the bells until the electricity is driven off.

WORKING POWER OF ELECTRICITY.

This may be shown in a variety of ways. The subjoined machine will

exhibit the principle upon which many ingenious toys may be made by the

young philosopher. In the figure A is a wooden board or stand, B B B B,

four pillars of glass, gutta-percha, or sealing-wax, having fine wires,

C C, stretched above. On these rest the rotatory wire or wheel F, having

its points turned the reverse ways. By means of a chain attached to the

conductor, and to the instrument at B, the electricity passes over the

pillar B, up the wire C into the wheel, and off at the points, which

causes it to be turned round on an inclined plane till it reaches the

top.

[Illustration]

THE ELECTRIFIED WIG.

While a person is on the electrical stool, if he be charged with much

electricity,

“Each hair will stand on end,

Like quills upon the fretful porcupine.”

[Illustration]

A wooden head--not your own, but a real wooden head--with a wig of

streaming hair, and a handsome face to correspond, may be made in the

following form, with a wire in the neck to support it by, and fixed in

the conductor of an electrical machine. When this is put in motion the

hair will rise up, as in the figure, in a manner to astonish even the

“big-wigs.”

IMITATION THUNDERCLOUDS.

[Illustration]

To show the manner in which thunderclouds perform their operations in

the air, A A is a wooden stand, on which are erected two uprights, B B;

C C are two small pulleys, over which a silken cord can pull easily; E

is another silken line stretched across from one upright to another; on

these silken cords two pieces of thin cardboard covered with tinfoil,

and cut so as to represent clouds, are to be fixed horizontally, and

made to communicate, by means of thin wires F and G, one with the

_inside_, and the other with the _outside_, of a charged jar, D. Now, by

pulling the loop of the silk line, the clouds will be brought near the

cloud 2; continue this slowly, until the clouds (which are furnished

with two small brass balls) are within an inch of each other, when a

beautiful flash, strongly resembling lightning in miniature, will pass

from one cloud to the other, restoring electrical equilibrium.

THE LIGHTNING STROKE IMITATED.

[Illustration]

If the jar D be put behind the stand, and the cloud 2 removed, a vessel

communicating by means of a wire with the outside of the jar may be swum

in water under the remaining cloud; the mast being made of two pieces,

and but slightly joined together, with a hollow space in one half of the

mast, into which the ends of the conductor pass, but do not touch,

leaving an interval of about a quarter of an inch between them. The

hollow is then filled with gun-cotton, and closed with cork. When the

cloud is passed over the vessel, the mast will be struck and shattered

to pieces. A strip of tinfoil, arranged with pins over the hollow part

of the mast, will show how a continuous conductor will convey the

discharge safely away.

THE SPORTSMAN.

This apparatus is capable of affording much amusement. A is a stand of

wood, B is a common Leyden jar, out of which proceed the wires H H--one

terminating in ball F, the other in the ball D--to which are attached a

number of pith birds by silken strings; E is a shelf for the birds to

rest upon; C is the sportsman; G his gun.

[Illustration]

To put this operation in motion the Leyden jar is to be charged with

electricity by affixing a chain to the bottom part of it, and connecting

it with an electrical machine in the usual manner, or by applying it to

a prime conductor, when the birds will fly off the knob to which they

are fixed in consequence of their being repelled. If the sportsman and

gun be then turned, so that the end of his gun shall touch the knob F,

an electric spark will pass from one to the other, a report will be

heard, and the birds will fall down as if shot, in consequence of the

electricity having been taken from the Leyden jar. There should be a

communication between the sportsman and the jar formed of tinfoil, or

some metal, as shown by the dotted line on the stand.

Such are a few of many numerous experiments which may be made by the

young experimenter, who is fond of science and has any ingenuity; but

should he like to amuse himself with an electrifying machine of little

cost, he may warm a sheet of brown paper, and then rub it briskly on a

teatray with india-rubber; on raising the paper in a dark room, he will

see many pretty electrical sparks.

The back of a black tom cat is sometimes recommended as a cheap

electrical machine; but as the wishes of the animal have to be

consulted, perhaps it is wiser to leave the cat alone.

[Illustration]

GALVANISM, OR VOLTAIC ELECTRICITY.

“To play with fire

They say is dangerous; what is it then

To shake hands with the lightning, and to sport

With thunder?”--TYLER.

Galvanism, or electricity of quantity, in contradistinction to

frictional electricity, called electricity of intensity, owes its name

to the experiments on animal irritability made in 1790 by M. Galvani, a

professor of anatomy at Bologna. These experiments were suggested by the

following circumstances.

ORIGIN OF GALVANISM.

It happened that the wife of Galvani, who was consumptive, was advised

to take as an article of food some soup made of the flesh of frogs.

Several of these creatures were killed and skinned, and were lying on

the table in the laboratory close to an electrical machine, with which a

pupil of the professor was making experiments. While the machine was in

action, he chanced to touch the bare nerve of the leg of one of the

frogs with the blade of the knife that he had in his hand, when suddenly

the whole limb was thrown into violent convulsions. Galvani was not

present when this occurred; but being informed of it, he immediately set

himself to investigate the cause. He found that it was only when a spark

was drawn from the prime conductor, and when the knife or any other good

conductor was in contact with the nerve, that the contracting took

place; and after a time he discovered that the effect was independent of

the electrical machine, and might be equally well produced by making a

metallic communication between the outside muscle and the crural nerve.

SIMPLE EXPERIMENT TO EXCITE GALVANIC ACTION.

If the young experimenter will obtain a piece of zinc of the size of

half a crown and place it on the top of his tongue, and place a

half-crown underneath it, and bring the edges of the half-crown and zinc

in contact in front of his tongue, he will notice a peculiar sensation

in the nerves of this organ, and some taste will be imparted to his

mouth at the moment of contact.

WITH METAL PLATES IN WATER.

[Illustration]

If we take two plates of different kinds of metal, platinum (or copper)

and zinc, for example, and immerse them in pure water, having wires

attached to them above, then if the wire of each is brought into contact

in another vessel of water, a galvanic circle will be formed, the water

will be slowly decomposed, its oxygen will be fixed on the zinc wire,

and at the same time a current of electricity will be transmitted

through the liquid to the platina or copper wire, on the end of which

the other element of water, namely, the hydrogen, will make its

appearance in the form of minute gas bubbles. The electrical current

passes back again into the zinc at the points of its contact with the

platina, and thus a continued current is kept up, and hence it is called

a galvanic circle. The moment the circuit is broken by separating the

wires the current ceases, but is again renewed by making them touch

either in or out of the water. If a small quantity of sulphuric acid be

added to the water, the phenomenon will be more apparent. The end of the

wire attached to the piece of platinum or copper is called the positive

pole of the battery, and that of the wire attached to the zinc the

negative pole.

The current of electricity here generated will be extremely feeble; but

this can be easily increased by multiplying the glasses and the number

of the pieces of metal. If we take six such glasses instead of one,

partially fill them with dilute sulphuric acid, and put a piece of zinc

and copper into each, connecting them by means of copper wire from glass

to glass through the whole series, a stronger current of electricity

will be the result. The experimenter must be careful not to let the wire

and zinc touch each other at the bottom of the tumblers, and must also

remember that the copper of glass 1 is connected with the zinc of glass

2, and so on.

[Illustration]

TO MAKE A MAGNET BY THE VOLTAIC CURRENT.

To effect this, make a connexion between the poles of the above or any

excited battery with the two ends of a wire formed into a spiral coil,

by bending common bonnet-wire closely round a cylinder, or tube, of

about an inch in diameter; into this coil introduce a needle or piece of

steel wire, laying it lengthways down the circles of the coil. In a few

minutes after the electric fluid has passed through the spiral wire, and

consequently round the needle or wire, the latter will be found to be

strongly magnetized, and to possess all the properties of a magnet.

EFFECTS OF GALVANISM ON A MAGNET.

If a galvanic current, or any electric current, be made to pass along a

wire under which, and in a line with it, a compass is placed, it will be

found that the needle will no longer point north and south, but will

take a direction nearly across the current, and point almost east and

west.

CHANGE OF COLOUR BY GALVANISM.

Put a teaspoonful of sulphate of soda into a cup, and dissolve it in hot

water; pour a little cabbage blue into the solution, and put a portion

into two glasses, connecting them by a piece of linen or cotton cloth

previously moistened in the same solution. On putting one of the wires

of the galvanic pole into each glass, the acid accumulates in the one,

turning the blue to a red, and the alkali in the other, rendering it

green. If the wires be now reversed, the acid accumulates eventually in

the glass where the alkali appeared, while the alkali passes to the

glass where the acid was.

THE GALVANIC SHOCK.

If the ends of the wires of a small galvanic battery are connected with

a proper electro-magnetic coil, which may now be purchased at a very

cheap rate, and the wires from the coil be placed in separate basins of

water, then, on dipping the fingers of each hand in the basin, a smart

shock will be felt, with a particular aching accompanied with trembling.

With a strong battery and larger coil this effect is felt as high as the

shoulders. The shock will also be felt by simply holding the wires of a

powerful galvanic battery, one in each hand, provided the hands be

moistened with salt and water. Several persons may receive the shock

from the battery and coil together by joining hands.

THE ELECTROTYPE.

The electro-galvanic current has in no case been more interestingly

employed than in the process of electrotyping. It consists of a mode of

obtaining the copy of coins, medals, engraved plates, and other objects,

which may be easily illustrated.

HOW TO MAKE AN ELECTROTYPE APPARATUS.

[Illustration]

Take an earthen jar and a porous tube; fill the tube with ten parts of

water and one of sulphuric acid; put it into the jar, into which pour as

much of a solution of sulphate of copper (blue vitriol) as will fill

three parts of it; place in the tube a piece of zinc, to which a copper

wire is soldered and bent round, so that one end be immersed in the

sulphate of copper; and a deposit of the copper will be immediately

formed upon the wire. If there be plenty of acid and water, so as to

allow of the action enduring for a long time, this process will go on

till it has deposited all the copper. This is the principle upon which

electrotyping proceeds,--a principle referable to electro-chemical

decomposition.

The diagram represents an outer vessel of wood, glass, or earthenware,

capable of holding a pint of liquid, within which there is suspended a

short lamp-glass A, the one end being open, and the other, B, closed

with a diaphragm of plaster of Paris; C is a small bag of crystals of

sulphate of copper, to keep up the strength of the solution; Z is the

zinc, and M the metal.

TO OBTAIN THE COPY OF A COIN OR MEDAL.

Never place the original medal in the apparatus, or the deposited copper

may adhere so tightly to it that the removal destroys the beauty of the

medal. Having taken an impression in sealing-wax, cover the latter with

black-lead, and attach a wire so that it is in contact with the

black-lead. To the wire and cast thus arranged a piece of sheet or cast

zinc, amalgamated with mercury, must be attached, and we are at once

furnished with the materials for the battery, as the object to be copied

supplies the place of the copper. The medal must always be placed

horizontally. Now let the apparatus be charged with the solution, by

pouring into the outer vessel a portion of the coppery solution, so that

it will stand about an inch above the medal; then pour in the glass the

dilute acid to the same height as the former; now introduce the zinc

into the acid, and the object to be copied into the solution of copper,

which will immediately be deposited on the medal, and when of a

sufficient thickness may be taken off.

HEAT.

HEAT, OR CALORIC.

The chief agent in causing the repulsion or separation of the particles

of bodies from each other is heat, or more correctly _caloric_, by which

is understood the unknown _cause_ of the effect called heat.

Philosophers are not agreed upon the nature of this wonderful agent. It

pervades all nature, is the cause of nearly all the changes that take

place both in organic and inorganic matter, and has great influence in

the meteorological phenomena which we observe in the atmosphere that

surrounds our planet. It appears to be intimately connected with light,

electricity, and magnetism,--subjects which the genius of Faraday and

others have investigated, and by their discoveries brought us nearer to

the knowledge of the real nature of these most wonderful forces.

Caloric, then, exists in all bodies, and has a constant tendency to

equalize itself, as far at least as its outward manifestation, called

temperature, is concerned; for if a _hot_ body be brought near colder

ones, it will give up heat to them, until by its loss and their gain

they all become of the same temperature; and this proceeds more or less

rapidly, according as the original difference of temperature was greater

or less. Some other circumstances also influence this equalization. The

converse will take place on introducing a cold body among warmer ones,

when heat will be abstracted from all the bodies within reach of its

influence, until it has absorbed sufficient caloric to bring its own

temperature to an equality with theirs. This is the true explanation of

the apparent production of _cold_. When, for instance, an iceberg comes

across a ship’s course, it appears to _give out_ cold, whereas, it has

abstracted the heat from the air and sea in its neighbourhood, and they

in turn act upon the ship and everything in it, until one common

temperature is produced in all the neighbouring bodies.

It does not follow that the bodies thus equalized in temperature contain

equal quantities of caloric; far from it. Each body requires a

particular quantity of caloric to raise its temperature through a

certain number of degrees; and such quantity is called its _specific_

caloric. A pound of water, for instance, will take just twice as much

caloric as a pound of olive oil, to raise its temperature through the

same number of degrees; the _specific_ caloric of water is therefore

double that of oil. Mix any quantity of oil at 60° of temperature with

an equal weight of water at 90°, and you will find the temperature of

the mixture to be nearly 80°, instead of only 74° or 75°, showing that

while the water has lost only 10° of caloric, the mixture has risen 20°.

If the oil be at 90°, and the water at 60°, the resulting temperature

will be only 70°, or thereabouts, instead of 75°, the mean; thus, here

the hot oil has lost 20°, while the mixture has risen only 10°; the

water, then, contains at the same temperature _twice_ as much caloric as

the oil; its specific caloric is _double_ that of the oil. This mean

temperature does result when equal weights of the _same_ body at

different temperatures are mixed together.

The sensations called heat and cold are by no means accurate measures of

the real temperature of any substances, for many causes influence these

sensations, some belonging to the substances themselves, others to the

state of our organs at the time. Every one has remarked that metals in a

warm room feel warmer, and in a cold room colder than wooden articles,

and these again than woollen or cotton articles of dress or furniture;

this arises from metals being what is termed better _conductors_ of heat

than wood, and this better than wool, &c., that is, they give out or

absorb caloric more rapidly than these last. Some philosophers, wishing

to ascertain how much heat the human body could endure, had a room

heated with stoves, every crevice being carefully stopped, until the

temperature rose so high that a beefsteak placed on the table was

sufficiently cooked to be eaten. They were dressed in flannel, and could

with impunity touch the carpets, curtains, &c., in the room; but the

iron handles, fire-irons, and all metallic substances, burnt their

fingers; and one who wore silver spectacles was obliged to remove them

to save his nose. The fallacy of our sensations may be easily shown by

taking two basins, placing in one some water at 100°, in another some

water at as low a temperature as can easily be procured--hold the right

hand in one, the left in the other, for a few minutes, and then mix

them, and place both hands in the mixture; it will feel quite _cold_ to

the hand that had been in the hotter water, and _hot_ to the other.

In order to arrive at a correct estimate of the temperature of bodies,

instruments are made use of called thermometers, or measurers of heat,

which show increase or diminution of temperature by the rising or

falling of a column of some fluid in a tube of glass, one end of which

is expanded into a bulb, and the other hermetically sealed. This effect

is produced by the expansion or swelling of the fluid as caloric is

added to, and its contraction when caloric is abstracted from it.

Coloured spirits of wine, or quicksilver, are the most usual

thermometric fluids, and the tube containing them is fixed to a wooden

or metallic frame, on which certain divisions are marked, called

degrees.

That in general use in England is called Fahrenheit’s, from the name of

the person who first introduced that particular scale. In this

thermometer, the point at which the mercury in the tube stands when

plunged into melting ice, is marked 32°, and the distance between that

point, and the point to which the mercury rises in boiling water, is

divided into 180 equal parts, called degrees; so that water is said to

boil at 212° = 180° + 32°. There are two other scales of temperature

used in different parts of the world, but it is not worth while to

notice them here.

Not only do different bodies at the same degree of temperature contain

very different quantities of caloric, but this also is the case with the

same body in different forms. Ice, water, and steam, are three forms of

the same body, but ice at 32° contains much less caloric than water at

the same temperature, and water at 212° contains much less caloric than

steam (or water in a state of vapour) at that temperature.

Place in a jar any given quantity of snow, or small pieces of ice, at

32°, and in another the same weight of water at 32°, pour on each an

equal weight of water at 172°, and you will find that in the first case

the ice will be melted, but the temperature will remain at 32° or

thereabouts, while the temperature of the water in the other vessel will

have risen to 100° or thereabouts, being as near as possible the half of

the excess of the temperature of the hot water, 140° over that of the

cold, namely 70° added to 32°, the original temperature. Now, what has

become of the heat which was added to the ice, and is apparently

lost?--it is _absorbed_ by the ice in its passage to the fluid state; so

that water may be said to be a compound of ice and caloric.

Again, take 10 ounces of water at about 50°, and add 1 oz. of water at

212°, and the temperature of the mixture will be about 66°; then

condense some steam at 212°, into another 10 oz. of water until it has

become 11 oz., and you will find the temperature will be nearly 212°.

Why does the ounce of steam at 212° raise the temperature of the water

so much higher than the ounce of water at the same temperature?

Obviously because it contains hidden in its substance a vast quantity of

caloric, not to be detected by the thermometer; in fact, that steam is a

compound of _water_ and caloric, as water is a compound of _ice_ and

caloric; and this caloric which exists, more or less, in all bodies

without producing any obvious effect, is called _latent_ caloric, from

the Latin verb _lateo_, to lie hid. The quantity of caloric thus

absorbed as it were by various bodies, differs for each body, and for

the same body in different forms, as mentioned above.

EXPANSION.

As a general rule, all bodies, whether solid, liquid, or gaseous, are

expanded by caloric. This may be shown by experiments in each form of

matter.

Have a small iron rod made, which when cold just passes through a hole

in a plate of metal; heat it, and it will no longer pass; after a time

the rod will return to its former temperature, and then will go through

the hole as before. The rod increases in length as well as width; if you

have a gauge divided into 1/100 of an inch, and place the rod in it when

cold, noting its position, on heating it will extend to a greater length

in the gauge, returning to its former place when cool.

The effect of caloric in causing fluids to expand is actually employed

as a measure of quantity in the thermometer, the rise of the fluid in

the tube when heated depending on the increased bulk of the fluid

occasioned by the addition of caloric. The same fact is to be noticed

every day when the cook fills the kettle, and places it on the fire. As

the water becomes warmer it expands, that is, takes up more room than it

did before, and the water escapes by slow degrees, increasing as the

heat increases, up to the point of boiling, when a sudden commotion

takes place from the condensation of a portion of the water into steam.

But it is in the form of vapour or gas, (which by the bye is not the

same thing,[9]) that the expansive force of caloric is most obvious. The

gigantic powers of the steam-engine depend entirely on the tendency of

vapour to expand on the addition of caloric; and this force of

expansion appears to have no limit; boilers made of iron plates an inch

or even more in thickness, and the buildings or ships containing them,

having been torn to pieces and scattered in all directions by the

expansive power of steam. Take a bladder, and fill it about half full of

air, and tie the neck securely; upon holding it to the fire it will

swell out, and become quite tense from the expansion of the contained

air.

[9] It may be well to state here, that by _vapour_ is generally

understood the aërial form of a substance usually existing in a

solid or fluid form at ordinary temperatures; as the vapour of

iodine, a solid; of mercury, water, spirits, and other fluids:

while the term _gas_ is applied to those bodies usually known in

the aërial state; thus oxygen, nitrogen, carbonic acid, hydrogen,

&c. &c., are called gases. It is, however, but an arbitrary

distinction; for many of these gases have, by the combined

influence of cold and powerful pressure, been converted into

fluids, and even solids--carbonic acid gas for instance!

The principal source of caloric is the sun, whose beams, diffused

through all nature by the refractive property of the atmosphere, are the

source of vitality both to vegetables and animals, and when concentrated

by a large convex lens, produce the most intense heat, sufficient to

light a piece of diamond, and melt platinum. Caloric is also produced or

evolved by combustion, by friction, percussion, chemical combination,

electricity, and galvanism.

The evolution of heat by friction may be witnessed daily in a thousand

instances. Lucifer matches are lighted by rubbing the highly inflammable

substances with which they are tipped against a piece of sand-paper.

Nearly all savage people procure fire by rubbing a piece of hard wood

violently against a softer piece. The axle-trees of steam-engines, and

even of carriages, have been known to be so heated by friction as to

endanger burning the carriage; and it is very usual to be obliged to

pour a quantity of cold water on the iron axle of the carriages of an

express train after an hour of constant and rapid work. If you merely

rub the blade of a knife rapidly on a piece of wood, it will become hot

enough to burn your hand.

Percussion is merely a more energetic kind of friction, and is often

resorted to by the blacksmith to light his furnace. He places a nail or

other piece of soft iron on his anvil, and beats it rapidly with the

hammer, when it becomes actually red hot. The production of sparks by

striking flint against steel, or two pieces of flint one against the

other, are familiar instances of heat produced by percussion.

One of the most powerful means of producing heat is the process of

combustion.

Combustion, as the word imports, is the _burning together_ of two or

more substances, a chemical union of oxygen generally with carbon and

hydrogen in some shape or other. In our ordinary fires we burn coal, a

hydro-carbon as it is called; and the gas which is now so universally

used for the purpose of illumination, is a compound of the same

bodies--so wax, tallow, oil of various kinds, both of animal and

vegetable origin, are all hydro-carbons.

On the application of a sufficient heat, and a free access of

atmospheric air, or of some other gas containing oxygen in a certain

state of combination, these bodies take fire, and continue to burn

either with flame, or a red or even white heat without flame, until they

are consumed; that is, until they have entered into new combinations

with the oxygen, and are converted into carbonic acid and water, the

carbon forming the first product, the hydrogen the other.

[Illustration]

The following experiment shows the production of heat by chemical action

alone. Bruise some fresh prepared crystals of nitrate of copper, spread

them over a piece of tin-foil, sprinkle them with a little water; then

fold up the foil tightly as rapidly as possible, and in a minute or two

it will become red-hot, the tin apparently burning away. This heat is

produced by the energetic action of the tin on the nitrate of copper,

taking away its oxygen in order to unite with the nitric acid, for

which, as well as for the oxygen, the tin has a much greater affinity

than the copper has.

Combustion without flame may be shown in a very elegant and agreeable

manner, by making a coil of platinum wire by twisting it round the stem

of a tobacco-pipe, or any cylindrical body, for a dozen times or so,

leaving about an inch straight, which should be inserted into the wick

of a spirit-lamp; light the lamp, and after it has burnt for a minute or

two extinguish the flame quickly; the wire will soon become red hot,

and, if kept from draughts of air, will continue to burn until all the

spirit is consumed. Spongy platinum, as it is called, answers rather

better than wire, and has been employed in the formation of fumigators

for the drawing-room, in which, instead of pure spirit, some perfume,

such as lavender water, is used; by its combustion an agreeable odour is

diffused through the apartment. These little lamps were much in vogue a

few years ago, but are now nearly out of fashion.

Experiments on combustion might be multiplied almost to any amount, but

the above will be sufficient for the present. When we come to treat of

the properties of the gases and some other substances, we shall have

occasion to recur to this subject.

The production of caloric by chemical combination may be exhibited by

mixing carefully one part of oil of vitriol with two of water, when

sufficient heat will be produced to boil some water in a thin and narrow

tube, which may be used as a rod to stir the mixture.

The production of heat by electric and galvanic agency belongs to

another subject. I will content myself with saying here, that these

forces afford the most powerful aid in decomposing and uniting various

bodies, and that it was by the immense power of a battery of 2,000 pairs

of plates, belonging to the Royal Institution in London, that Sir H.

Davy discovered the metallic bases of the alkalies and earths.

HYDRAULICS.

The science of Hydraulics comprehends the laws which regulate

non-elastic fluids in motion, and especially water, &c.

[Illustration]

Water can only be set in motion by two causes--the pressure of the

atmosphere, or its own gravity. The principal law concerning fluids is,

that they always preserve their own level. Hence water can be

distributed over a town from any reservoir that is higher than the

houses to be supplied; and the same principle will enable us to form

fountains in a garden, or other place. Should any of our young friends

wish to form a fountain, or jet d’eau, they may, by bringing a pipe from

T, a water-tank, which should be at the upper part of the house, convey

the water down to the garden. Then by leading it through the earth,

underneath the path or grass-plot, and turning it to a perpendicular

position, the water will spring out, and rise nearly as high as the

level of that in the tank. The part of the pipe at B should have a

turnkey, so that the water may be let on or shut off at pleasure.

THE SYPHON.

[Illustration]

The syphon B is a bent tube, having one leg shorter than the other. It

acts by the pressure of the atmosphere. In order to make a syphon act,

it is necessary first to fill both legs quite full of the fluid; and

then the shorter leg must be placed in the vessel to be emptied.

Immediately upon withdrawing the finger from the longer leg, the liquor

will flow. Any young person may form a syphon by a small piece of leaden

pipe, bent into the form above.

THE PUMP.

[Illustration]

The action of the common pump is as follows: When the handle A is

raised, the piston-rod B descends, and brings the piston-valve, called

the sucker, or bucket, to another valve, C, which is fixed, and opens

inwards towards the piston. When the handle is drawn down, the piston is

raised, and, as it is air-tight, a vacuum is produced between the two

valves; the air in the barrel of the pump, betwixt the lower valve and

the water, then forces open the lower valve, and rushes through to fill

up this vacuum; and the air in the pump being less dense than the

external atmosphere, the water is forced a short way up the barrel. When

the piston again descends to the lower valve, the air between them is

again forced out by forcing open the upper valve; and when the piston is

raised, a vacuum is again produced, and the air below the lower valve

rushes up, and the water in consequence is again raised a little

further. This operation continues until the water rises above the lower

valve; at every stroke afterwards, the water passes through the valve of

the descending piston, and is raised by it, on its ascent, until it

issues out of the spout.

THE HYDRAULIC DANCER.

[Illustration]

Make a little figure of cork, in the shape of a dancing mountebank,

sailor, &c. In this figure place a small hollow cone, made of thin leaf

brass. When this figure is placed upon any jet d’eau, such as that of

the fountain recommended to be constructed, it will be suspended on the

top of the water, and perform a great variety of amusing motions. If a

hollow ball of very thin copper, of an inch in diameter, be placed on a

similar jet, it will remain suspended, turning round and spreading the

water all about it.

THE WATER SNAIL, OR ARCHIMEDEAN SCREW,

[Illustration]

may easily be constructed. Purchase a yard of small leaden pipe, and

twist it round a pole, as in the following figure, A; place a handle at

its upper end, B, and let its lower end rest in the water. Between the

last turn of the pipe and the orifice place a paddle-wheel, C. Now,

should the water be that of a running stream, the force of the stream

will turn the pipe, and the water will rise in it till it empties itself

into the trough at D. Should the water have no motion, the turning of

the handle at B will elevate the water from the lower to the higher

level.

[Illustration]

MAGNETISM.

The attractive power of the loadstone has been known from a very remote

period. The natural magnet appears native in a grey iron ore in

octahedral crystals, composed of 168 parts of iron, and 64 parts of

oxygen, Fe₃O₄. Its properties seem to have been studied in Europe during

the dark ages, and a directive power is alluded to by Cardinal James de

Vitri, who flourished about the year 1200, who observed, that it was

indispensable to those who travel much by sea.

In modern times, the history as well as the nature of the magnet has

engaged remarkable attention; and it has been determined beyond all

dispute that the magnet was used by the Chinese under the name of the

_tche-chy_ (directing-stone) about 2604 years before Christ. It passed

from them to the Arabs, and was first used in Europe after the Crusades;

and Ludi Vestomanus asserts, that about the year 1500 he saw a pilot in

the East Indies direct his course by a magnetic needle like those now in

use.

RELATION OF MAGNETISM TO ELECTRICITY.

The most remarkable theories have been invented to account for the

phenomena of magnetism. Halley imagined magnetic globes to be moving to

and fro in the interior of the earth. Barlow’s theory, which refers the

whole to electrical currents, is the most rational. Dr. Faraday, for

whose kindness to us in early days we always feel grateful, in a series

of very curious experiments, has succeeded in identifying magnetism with

galvanism, by directing galvanic currents at right angles to the

direction of powerful magnets. And its connexion with this and the

common species of electricity has deprived it of all its conjuring

powers, and reduced it to the well-defined action of electrical bodies.

It is not for us to write either a history of this interesting subject,

or to treat it as a science to be acquired; but as it embodies a great

number of most instructive and amusing experiments, we think it proper

to introduce it here.

TO MAKE ARTIFICIAL MAGNETS.

This may be done by stroking a piece of hard steel with a natural or

artificial magnet. Take a common sewing-needle and pass the north pole

of a magnet from the eye to the point, pressing it gently in so doing.

After reaching the end of the needle the magnet must not be passed back

again towards the eye, but must be lifted up and applied again to that

end, the friction being always in the same direction. After repeating

this for a few times the needle will become magnetised, and attract iron

filings, &c.

HOW TO MAGNETISE A POKER.

Hold it in the left hand in a position slightly inclined from the

perpendicular, the lower end pointing to the north, and then strike it

smartly several times with a large iron hammer, and it will be found to

possess the powers of a magnet, although but slightly.

TO SHOW MAGNETIC REPULSION AND ATTRACTION.

Suspend two short pieces of iron wire, N S, N S, so that they will hang

in contact in a vertical position. If the north pole of a magnet N be

now brought to a moderate distance between the wires, they will recede

from each other, as in figure 1.

[Illustration: _Fig. 2_ _Fig 1._]

The ends S S being made south poles by induction from the north pole N,

will repel each other, and so will the north poles N N. This separation

of the wires will increase as the magnet approaches them, but there will

be a particular distance at which the attractive force of N overcomes

the repulsive force of the poles S S, and causes the wires to converge,

as in figure 2; the north poles N N still exhibiting their mutual

repulsion.

NORTH AND SOUTH POLES OF THE MAGNET.

Each magnet has its poles, north and south--the north or south poles of

one magnet, repel the north and south pole of another. If a magnet, as

in the following figure, be dipped in some iron filings, they will be

immediately attracted to one end. Supposing this to be the north pole,

each of the ends of the filings, not in contact with the magnet, will

become north poles, while the ends in contact will by induction become

south poles. Both will have a tendency to repel each other, and the

filings will stand on the magnet as in the figure.

[Illustration]

POLARITY OF THE MAGNET.

[Illustration]

The best method of proving this is to take a magnet or a piece of steel

rendered magnetic, and to place it on a piece of cork by laying it in a

groove cut to receive it. If the cork be placed in the centre of a basin

of water, and allowed to swim freely on its surface, so that it is not

attracted by the sides of the basin, it will be found to turn its north

pole to the north, and its south pole to the south, the same as the

mariner’s compass. If you fix two magnets in two pieces of cork, and

place them also in a basin of water, and they are in a parallel position

with the same poles together, that is, north to north, and south to

south, they will mutually repel each other; but if the contrary poles

point to one another, as north to south, they will be attracted.

THE MAGNETIC FISH.

[Illustration]

Fish are to be purchased at the toy-shops, by which the young

“magnétique” may perform this experiment; they are made hollow, and will

float on the water. In the mouth of each should be inserted a piece of

magnetic wire. The angling rod is like any other rod, and has a silken

thread for a line, and an iron hook also strongly magnetised. To catch

the fish it is only necessary to put the hook in contact with the noses

of the fish, and they will be taken without any of the baits mentioned

in the former part of this work.

THE MAGNETIC SWAN.

[Illustration]

The figure of a swan should be cut in cork, and within its beak a small

strongly magnetised piece of steel should be placed. The swan should

then be covered with a coating of white wax, and fashioned further into

the shape of a swan, and glass beads may be placed in its head for eyes.

This should be placed in a small tub or large basin of water, and to

make it swim about, you should place in a white stick about nine inches

long a magnetic bar, on which the north and south poles are marked. If

you wish to bring the swan towards you, present to him the north pole of

the wand, if you wish it to retire, present the south pole, and thus you

may direct the swan to any part you desire.

TO SUSPEND A NEEDLE IN THE AIR BY MAGNETISM.

Place a magnet on a stand to raise it a little above the table; then

bring a small sewing-needle containing a thread, within a little of the

magnet, keeping hold of the thread to prevent the needle from attaching

itself to the magnet. The needle in endeavouring to fly to the magnet,

and being prevented by the thread, will remain curiously suspended in

the air, reminding us of the fable of Mahomed’s coffin.

TO MAKE ARTIFICIAL MAGNETS WITHOUT THE AID EITHER OF NATURAL LOADSTONES

OR ARTIFICIAL MAGNETS.

[Illustration]

Take an iron poker and tongs, or two bars of iron, the larger and the

older the better, and fixing the poker upright, hold to it with the left

hand near the top P by a silk thread, a bar of soft steel about three

inches long, one fourth of an inch broad, and one twentieth thick; mark

one end, and let this end be downwards. Then grasping the tongs T with

the right hand a little below the middle, and keeping them nearly in a

vertical line, let the bar B be rubbed with the lower end L of the

tongs, from the marked end of the bar to its upper end about ten times

of each side of it. By this means the bar B will receive as much

magnetism as will enable it to lift a small key at the marked end; and

this end of the bar being suspended by its middle, or made to rest on a

joint, will turn to the north, and is called its north pole, the

unmarked end being the south pole. This is the method recommended by Mr.

Caxton, in his process, which he regarded superior to those in former

use, and of which a more detailed account will be found in his

interesting volume.

HORSE-SHOE MAGNETS.

[Illustration]

The form of a horse-shoe is generally given to magnetised bars, when

both poles are wanted to act together, which frequently happens in

various experiments, such as for lifting weights by the force of

magnetic attraction, and for magnetising steel bars by the process of

double touch, for which they are exceedingly convenient. The following

is the method of making a powerful magnetic battery of the horse-shoe

form. Twelve bars or plates of steel are to be taken, and having been

previously bent to the required form, that is, the horse-shoe shape,

they are then bound together by means of rivets at their ends; before

being finally fastened they are each separately magnetised, and

afterwards finally united.

Horse-shoe magnets should have a short bar of soft iron adapted to

connect the two poles, and should never be laid by without such a piece

of iron adhering to them. Bar magnets should be kept in pairs with their

poles turned in contrary directions, and they should be kept from rust.

Both kinds of magnets have their power not only preserved but increased,

by keeping them surrounded with a mass of dry filings of soft iron, each

particle of which will re-act by its induced magnetism upon the point of

the magnet to which it adheres, and maintain in that point its primitive

magnetic state.

EXPERIMENT TO SHOW THAT SOFT IRON POSSESSES MAGNETIC PROPERTIES WHILE IT

REMAINS IN THE VICINITY OF A MAGNET.

[Illustration]

Let M be a magnet and K a key, held horizontally near one of its poles,

or near its lower edge. Then if another piece of iron, such as a small

nail, be applied to the other end of the key, the nail will hang from

the key, and will continue to do so while the magnet is slowly

withdrawn; but when it has been removed beyond a certain distance, the

nail will drop from the key, because the magnetism induced in the key

becomes at that distance too weak to support the weight of the nail.

That this is the real cause of its falling off may be proved by taking a

still lighter fragment of iron, such as a piece of very slender wire,

and applying it to the key. The magnetism of the key will still be

sufficiently strong to support the wire, though it cannot the nail, and

it will continue to support it even when the magnet is yet further

removed; at length, however, it drops off.

ELECTRO-MAGNETISM.

The identity of magnetism with electricity alluded to in a former

paragraph, has led to the formation of a new science under the above

name, and to some of the interesting experiments connected with it, we

shall briefly allude for the amusement of the young reader.

POWER OF THE ELECTRO-MAGNET.

[Illustration]

The same influence which affects the magnetic needle already described,

will also communicate magnetism to soft iron. If a bar of that metal

bent, as in the drawing, be surrounded with a common bonnet wire, or a

copper wire prevented from touching the iron by a winding of cotton or

thread, and then if a current of voltaic electricity be sent through the

wire, the bar becomes a powerful magnet, and will continue so as long as

the connexion with the battery is preserved. On breaking the contact,

the magnetism disappears. This experiment may be easily made by the

young reader with a horse-shoe magnet, surrounded by several coils of

wire. P is the positive, and N the negative pole.

THE MARINER’S COMPASS AND EXPERIMENTS WITH A POCKET COMPASS.

The mariner’s compass is an artificial magnet fitted in a proper box,

and consists of three parts--1, the box; 2, the card or fly; and 3, the

needle. The box is suspended in a square wooden case, by means of two

concentric brass circles called gimbals, so fixed by brazen axes to the

two boxes, that the inner one, or compass-box, retains a horizontal

position in all motions of the ship. The card is a circular piece of

paper which is fastened upon the needle, and moves with it. The outer

edge of the card is divided into thirty-two points, as shown in the

engraving, called points of the compass. The needle is a slender bar of

hardened steel, having a hollow agate cup in the centre, which moves

upon the point of a pivot made of brass.

[Illustration]

VARIATION OF THE NEEDLE.

The magnetic needle does not point exactly north and south, but the

north pole of the needle takes a direction to the west of the true

north. It is constantly changing, and varies at different parts of the

earth, and at different times of the day.

DIP OF THE NEEDLE.

Another remarkable and evident manifestation of the influence of the

magnetism of the earth upon the needle is the inclination or dip of the

latter, which is a deviation from its horizontal place in a downward

direction in northern regions of its north, and in southern regions of

its south pole. In balancing the needle on the card, on account of this

dipping, a small weight or moveable piece of brass is placed on one end

of the needle, by the shifting of which either nearer to or further from

the centre, the needle will always be balanced.

USEFUL AMUSEMENT WITH THE POCKET COMPASS.

Pocket compasses are to be bought for five or six shillings, and may be

used in many ways. In travelling over mountains or a wide extended moor,

they are indispensably necessary; and no one should go a tour into

Wales, Scotland, or the lakes without such a companion, and it will be a

very useful and amusing exercise for any young person to take the

bearings of his own or some particular locality, and make out what may

be called a bearing card. This he may easily do in the following manner.

Supposing he wishes, for instance, to take the bearings of his own

house, he has nothing to do but to set his pocket compass upon a map of

the district,--a county map will do very well, unless his house stands

on the verge of a county, then two county maps will be necessary. He

must make the north of the map exactly coincide with the north, as

indicated by his compass, and having fixed his map in this situation, he

should take a ruler and piece of paper, and dot down the exact bearings

of each important town, or place, or village, around him. Let him

suppose himself, for instance, in the town of Cambridge, and laying down

his map as indicated by the compass, north to north and south to south,

he will find the following places due north, Wilberton, Wentworth;

Little Wilbraham, Teversham, due east; Duxford and Chesterfield, south;

Coton and St. Neots in Huntingdonshire, west. The other points of the

compass may be filled up in the same manner. Should therefore our young

friend be upon any elevated situation near his own dwelling, or upon any

other elevated spot from which the bearings have been taken, he will be

able to inform his young friends that such and such a place lies in such

a direction, that this place lies due north, the other north-west, a

third south-east, the fourth south-west, &c. &c.

[Illustration]

INTERESTING PARTICULARS CONCERNING THE MAGNET.

Fire-irons which have rested in an upright position in a room during the

summer months are often highly magnetic.

Iron bars standing erect, such as the gratings of a prison cell, or the

iron railings before houses, are often magnetic.

The great iron-clad ships, which have now replaced the wooden walls of

Old England, are powerfully magnetic, and therefore affect the compass

by which the vessel is steered; ingenious arrangements are therefore

made to correct the effect of the local attraction, so that the

man-of-war may be steered correctly.

Magnetism may be made to pass through a deal board; to exhibit which,

lay a needle on the smooth part above, and run a magnet along the under

side, and the needle will be found to follow the course of the magnet. A

magnet dipped into boiling water loses part of its magnetism, which

however returns upon its cooling.

A sudden blow given to a magnet often destroys its magnetic power.

[Illustration]

[Illustration]

MECHANICS.

“These are machinations comical.”--FORD.

There is no subject of such importance as Mechanics, as its principles

are founded upon the properties of matter and the laws of motion; and in

knowing something of these, the tyro will lay the foundation of all

substantial knowledge.

The properties of matter are the following: Solidity (or

Impenetrability), Divisibility, Mobility, Elasticity, Brittleness,

Malleability, Ductility, and Tenacity.

The laws of motion are as follow:--

1. Every body continues in a state of rest or of uniform rectilineal

motion, unless affected by some extraneous force.

2. The change of motion is always proportionate to the impelling force.

3. Action and reaction are always equal and contrary.

EXPERIMENT OF THE LAW OF MOTION.

In shooting at “taw,” if the marble be struck “plump,” as it is called,

it moves forward exactly in the same line of direction; but if struck

sideways, it will move in an oblique direction, and its course will be

in a line situated between the direction of its former motion and that

of the force impressed. This is called the resolution of forces.

BALANCING.

The centre of gravity in a body is that part about which all the other

parts equally balance each other. In balancing a stick upon the finger,

or upon the chin, it is necessary only to keep the chin or finger

exactly under the point which is called the centre of gravity.

THE PRANCING HORSE.

[Illustration]

Cut out the figure of a horse, and having fixed a curved iron wire to

the under part of its body, place a small ball of lead upon it. Place

the hind legs of the horse on the table, and it will rock to and fro. If

the ball be removed, the horse would immediately tumble, because

unsupported, the centre of gravity being in the front of the prop; but

upon the ball being replaced, the centre of gravity immediately changes

its position, and is brought under the prop, and the horse is again in

equilibrio.

TO CONSTRUCT A FIGURE, WHICH, BEING PLACED UPON A CURVED SURFACE, AND

INCLINED IN ANY POSITION, SHALL, WHEN LEFT TO ITSELF, RETURN TO ITS

FORMER POSITION.

The feet of the figure rest on a curved pivot, which is sustained by two

loaded balls below; for the weight of these balls being much greater

than that of the figure, their effect is to bring the centre of gravity

of the whole beneath the point on which it rests; consequently the

equilibrium will resist any slight force to disturb it.

TO MAKE A CARRIAGE RUN IN AN INVERTED POSITION WITHOUT FALLING.

[Illustration]

It is pretty well known to most boys, that if a tumbler of water be

placed within a broad wooden hoop, the whole may be whirled round

without falling, owing to the centrifugal force. On the same principle,

if a small carriage be placed on an iron band or rail, it will ascend

the curve, become inverted, and descend again, without falling.

TO CAUSE A CYLINDER TO ROLL BY ITS OWN WEIGHT UP-HILL.

[Illustration]

Procure a coffee-canister, and loading it at F with a piece of lead,

which may be fixed in with solder, the position of the centre of gravity

is thus altered. If a cylinder so constructed be placed on an inclined

plane, and the loaded part above, it will roll up-hill without

assistance.

THE BALANCED STICK.

[Illustration]

Procure a piece of wood, about nine inches in length and about half an

inch in thickness, and thrust into its upper end the blades of two

penknives, on either side one. Place the other end upon the tip of the

fore-finger, and it will keep its place without falling.

THE CHINESE MANDARIN.

[Illustration]

Construct out of the pith of the elder a little mandarin; then provide a

base for it to sit in, like a kettle-drum. Into this put some heavy

substance, such as half a leaden bullet; fasten the figure to this, and

in whatever position it may be placed, it will, when left to itself,

immediately return to its upright position.

TO MAKE A SHILLING TURN ON ITS EDGE ON THE POINT OF A NEEDLE.

[Illustration]

Take a bottle, with a cork in its neck, and place in it, in a

perpendicular position, a middle-sized needle. Fix a shilling into

another cork, by cutting a nick in it; and stick into the same cork two

small table-forks, opposite each other, with the handles inclining

outwards and downwards. If the rim of the shilling be now poised on the

point of the needle, it may easily be made to spin round without

falling, as the centre of gravity is below the centre of suspension.

THE DANCING PEA.

[Illustration]

If you stick through a pea, or small ball of pith, two pins at right

angles, and defend the points with pieces of sealingwax, it may be kept

in equilibrio at a short distance from the end of a straight tube, by

means of a current of breath from the mouth, which imparts a rotatory

motion to the pea.[10]

[10] The pins are only used to hold the pea steady before it is blown

from the pipe, as the pea alone will dance quite as well.

OBLIQUITY OF MOTION.

Cut a piece of pasteboard into the following shape, and describe on it

a spiral line; cut this out with a penknife, and then suspend it on a

large skewer or pin, as seen in the engraving. If the whole be now

placed on a warm stove, or over the flame of a candle or lamp, it will

revolve with considerable velocity. The card, after being cut into the

spiral, may be made to represent a snake or dragon, and when in motion

will produce a very pleasing effect.

[Illustration]

THE BRIDGE OF KNIVES.

[Illustration]

Place three glasses, A A A, in the form of a triangle, and arrange three

knives upon them, as shown in the figure,--the blade of No. 1 over that

of No. 2, and that over No. 3, which rests on No. 1. The bridge so made

will be self-supported.

THE TOPER’S TRIPOD.

[Illustration]

Place three tobacco-pipes in the position shown in the engraving, the

mouth of the bowls downwards, and the lower end of the stems upon the

stem just by the bowls. This tripod, if carefully put together, will

support considerably more than a pot of “Lockwood’s home-brewed,”

equally celebrated with the trick.

THE MICROSCOPE.

At any time of the year or hour of the day there are few pursuits more

interesting, and at the same time instructive, than the study of Nature

by means of the microscope.

This instrument has revolutionized science, solved many problems that

had wearied the souls of older naturalists, and even in its simplest

form is beyond all value to those who love Nature and the objects which

they see around them. The microscope opens a new world to us. When the

first telescope was directed to the heavens, and unlocked the mysteries

of the skies, when it crumbled into dust all the theories of the past

centuries, and told mankind that the planets were not merely instruments

of fortune-telling, whose voices were intelligible to a chosen few, but

orbs far vaster than our own; even then the new world of thought into

which man entered was no wider than that which is displayed by the

poorest lens that possesses the power of magnifying.

All of us must admire the more than awful grandeur of that universe

whereof we form so infinitesimal a part, wherein the stars are scattered

as the sand on the sea-shore, and every star a sun, the centre of a

system of orbs too distant for the eye of man to perceive. Looking at

our nearest planet, and observing on her face vast mountain-chains,

ravines into which the light of the sun can never penetrate, and

volcanoes whose craters are so wide that they would take in the whole of

London, the whole of Birmingham, and all the country between them, we

can judge by analogy of the unseen wonders which must exist in the world

beyond our ken.

But to him who can read Nature rightly, the microscope is a teacher as

grand as its sister instrument, and the awful magnificence of Nature is

as evident in a midge’s wing as in the more patent glories of the sun,

moon, and stars. In the following pages we hope to put the readers of

this book in the way to read their microscope rightly--possibly to make

it--and to show that much can be done with small means when “there’s a

will,” and to indicate to them that objects of no small interest can be

found without stirring from the room in which we sit, or even from the

table on which our microscope is placed.

Some of our readers may say, when they read the heading of this paper,

that they should like a microscope very much, but that they have no

money to buy it, and that their parents cannot afford one.

This is just the feeling which we used to have when a boy, for in those

days microscopes were microscopes indeed, and you had your choice

between a little instrument, with a series of brass cups, having glasses

in them, which magnified slightly but defined clearly, or a great

composition of brass and iron, looking like a rocket-tube, with an

eye-piece at one end and a glass shot at the other. In was very costly,

very imposing, and magnified very highly; but it strained the eyes

painfully, had no defining capacities, and made all the objects look as

if they were seen through a thick fog. Practically, therefore, the

former was the only instrument that was available.

A still more useful instrument, however, was that which can always be

obtained for a few shillings, and which is now made wonderfully cheap

and wonderfully good; we mean the double or treble pocket-lens. So we

say, if you cannot afford a really good microscope, do not waste your

money upon inferior and pretentious instruments, but get a sound

pocket-lens.

It has a thousand advantages. It is portable, and is even more useful in

the fields than in the house. It defines very clearly, and needs little

trouble in manipulation. We need not say how difficult is the task of

getting a complicated instrument to define properly, how impossible with

a bad one. The object and the glass can be held in any light,--a matter

of no small consideration when examining anything new, and trying to

make out its structure. It is not easily put out of order, and if

treated with the most ordinary care, will last for a lifetime.

You can push it under water, and it will magnify as well as in the air;

and if you are wandering on the river-side, you can lie down on the

bank, dip the upper part of your head into the water, together with the

glass, and watch carefully the subaquatic objects without removing them.

The water will not hurt the eye in the least, though a non-swimmer may

perhaps find a little difficulty in his first attempt. It makes a good

burning-glass, should fire be needed, and no other means of procuring a

spark be at hand. It can be used so as to show the principle of a camera

obscura, and to illustrate the manner in which photographic portraits

are taken. It can be made into an admirable dissecting microscope, and

needs scarcely any practice in the manipulation. These are some of its

advantages, and there are many others which need not be mentioned.

Even if you should be able to procure a good microscope, get a

pocket-lens as well, for you will want them both, and we may say that

the most practised microscopists, and those who are possessors of the

most elaborate instruments, are the very men who are most certain to

have a pocket-lens about them, and to use it most frequently. Practise

well with the pocket-lens before you meddle with the compound

microscope. You will waste no time, but will rather gain by it; for you

will be learning the rudiments of a new science, and laying a solid

foundation on which to build. Whenever we see a lad take out his

pocket-lens in a business-like way, use it skilfully, and put it back

with a mechanical facility that tells of constant practice, we know that

there is a lad who has learned the chief lesson of a

naturalist,--namely, the art of observing. We speak highly of the

pocket-lens, because we think highly of it and owe much to it.

One or two practical remarks on the proper handling of the pocket-lens

may be of use. Do not always employ the same eye in looking through the

lens, but use the eyes alternately. There is always a temptation to

employ the same eye, which thus receives a kind of training in vision;

but it is a temptation always to be resisted. With some persons the

right eye is most in favour, and with others the left; and when the

favourite eye gets all the work, it too frequently suffers. Whether you

look with the right or the left eye, _keep both eyes open_.

It is a pitiful sight to see a human face all screwed up into a corner,

the lids of the unused eye convulsively squeezed together, and the mouth

slanting upwards, as if in sympathy with the eye. Not only does the

human face become repulsively mean and portentously ugly by such action,

but the sight of the eye is seriously strained, and sometimes impaired

for life. At first the beginner will find a little difficulty in

restricting his vision to one eye while the other remains open, just as

a beginner on the pianoforte feels himself puzzled when he tries to make

his right hand go one way and his left hand another; but in either case

a little practice and plenty of perseverance are sure to overcome all

obstacles, and in a wonderfully short time the difficulty will not only

be overcome, but forgotten.

We speak here with some feeling, because, while engaged on a work on the

microscope, we were necessarily obliged to work much at night, and

inadvertently employed the left eye more than the right; the consequence

of which imprudence was that we have been obliged ever since that time

to give the left eye perfect rest, as far as artificial vision goes,

and, except when looking through a binocular instrument, we have not

ventured to use it either to a microscope or telescope. The vision

accommodates itself to circumstances with wonderful ease, and the

observer learns the curious art of cutting off all communication between

the unused eye and the brain; so that, although the objects around may

imprint themselves upon the retina, the mind is as totally unconscious

of them as if they had no existence.

If possible, always examine an object _without removing it_, as thereby

you see it as it is, without altering any of the conditions with which

it is surrounded. Should this not be practicable, take the object to be

viewed in the left hand and the lens in the right. Place the wrists of

the two hands together, and then you will find that one supports the

other, and that the lens can be held in the proper focus without the

least difficulty. After you have used the lens for some little time, you

will learn to hit upon the right focus almost to a hair’s breadth,--so

as to lose no time, a matter of some importance when a living creature

is to be examined, especially if it be in motion.

As to the selection of objects, none is necessary. Look at everything;

and the uglier and more unpromising it is, let it be the closer

examined. We do not merely use our aids to vision for the sake of seeing

beautiful things, though the microscopist sees more beauty in a day than

others will see in a year. We want to see how the world and its

constituent parts are made; and though admiration will not be wanting,

yet it does not, or ought not, to hold the first place. Always have a

motive for looking at every object, and if you have none, try to make

one. One of our friends, known by name at least to most of my readers,

struck out, some years ago, a most curious train of thought while

looking at an object which is seen daily by thousands of human beings,

and will probably soon give the public the benefit of it. We have seen

the object hundreds of times, but the ideas which it suggested did not

happen to occur to us.

[Illustration]

We are now about to suggest a very simple piece of mechanism, by which

the pocket-lens can be converted into a microscope that will serve for

dissection and many other purposes. The accompanying sketch is taken

from an instrument of our own manufacture. It is of very rough make, and

by an old Indian officer would be contemptuously termed “cutcha.”

Measured, however, by its performance, it is quite as satisfactory as

those instruments which are made by professed opticians, and which the

same old Indian would class under the honoured title of “pucka.”

Melt three or four pounds of lead in an iron ladle, and make a mould,

consisting of a hollow hemisphere of paper or cardboard, through the

centre of which an iron rod has been passed. The hollow of the paper

should resemble an ordinary saucer. Pour the lead into the saucer, and

let it cool. The paper mould will be scorched by the heat and rendered

useless, but an outer coating of lead will be cool and hard before the

paper is quite destroyed. The rod and leaden stand will now appear as in

the illustration. Next take a piece of stout brass wire and a wine-cork;

twist the wire round the cork several times; cut off one end close to

the cork; sharpen the other, and turn it up as seen in the engraving.

Bore a hole through the cork, just large enough to allow the upright rod

to slip through it, and there is the “stand” of your microscope. Now

take your pocket-lens, and get an optician to bore a hole through one

end of it, just large enough to receive the upturned end of the wire;

slip the lens on the wire, and the microscope is complete.

The cork, though grasping the upright stem with tolerable firmness, can

be slid up and down so as to insure the correct focus, and can be pushed

aside whenever the object has to be viewed with the naked eye and must

not be removed from its place. This instrument is a capital one for

dissecting purposes, and will answer quite as well as those expensive

affairs that are to be purchased in the shops. If, however, our readers

would like to possess a real and well-made instrument, he cannot do

better than get one of Ross’s Dissecting Microscopes, which are very

steady, and, as may be seen, can be adjusted to almost any position. A

rack-and-pinion movement for elevating or lowering the sliding pillar

would be useful.

[Illustration: ROSS’S DISSECTING MICROSCOPE.]

If the object be transparent, and requires to be seen by transmitted

light, the following plan will answer:--Take a thin piece of wood, cut

or punch a round hole out of the middle, and support it on four legs.

Wires or wooden pegs fixed in corks will answer the purpose well, and if

the corks be glued to the corners of the board, the legs can be inserted

or removed at pleasure. The wood of which cigar-boxes are made will

answer the purpose very well. Its dimensions should be about three

inches in length by two in width. Now buy one of the doll’s

looking-glasses that are sold for a penny, and put it under the stand.

Lay a flat piece of glass over the hole, place the object upon it, and

direct the light through it by means of the mirror below. If such a

mirror cannot be obtained, it is easy enough to make one, by mounting a

piece of looking-glass in a cork frame, and making it swing on pivots,

like the glasses of our dressing-rooms.

The young microscopist must remember that when he is examining any

object by transmitted light, he must arrange it as flatly as possible on

the glass. In many cases, a still neater manipulation is required,--as,

for example, when the petals of flowers are under examination. Thin

glass is to be purchased at any optician’s, and if cut in squares,

instead of circles, is very much cheaper, and quite as useful for all

practical purposes. Lay the petal on the glass plate, place a piece of

the thin glass upon it, and press it gently while examining it. If it

still remains thick and dull, put a drop of pure water on the petal, and

replace the thin glass, when the structure will almost invariably be

detected.

Everything depends on the proper management of the object and the

arrangement of the light. Some opaque objects can be seen best by direct

light, and others by transmitted light. If a leaf be examined,

particularly if it be a thick and heavy one, like that of the ivy, the

upper and lower membranes must be stripped apart,--a task which is

easily performed by tearing a small slit, and then ripping it smartly

across. A pair of forceps will be required for this and other delicate

work, and may be obtained at a cheap rate. Care must be taken to keep

the points exactly even, and if at any time one of them appears to be

shorter than the other, they should be rubbed on a hone until they are

brought perfectly level.

[Illustration]

These should be made of steel; but the young microscopist will find that

a second pair made of brass, and much rougher in finish, are invaluable

aids as he takes his walks into the country. By their aid he can pick up

minute objects, draw insects out of crevices without damaging them, and

pluck the tiniest flowers without harming their petals. They can be

carried in the waistcoat pocket, and the cost is sixpence. Any lad who

knows how to handle solder can make a pair for himself in a few minutes.

A penknife with one blade kept scrupulously sharp is essential, and we

have found an old lancet of the greatest service. Lancets have gone so

much out of fashion, that the second-hand instrument shops abound with

them. We did not allow our own lancet to be shut up, but removed the

blade from the tortoise-shell handle, and fixed it upon a wooden handle,

about four inches in length, so that it looked very clumsy, but was

extremely useful.

Two pairs of scissors are needful,--one very fine, and the other

moderately strong. Both pairs, however, must have very short blades and

very long handles, and the scissors such as ladies use are of very

little use, the short handles causing the fingers of the right hand to

shade the object. As to the fine pair, it is hardly possible to have

the handles too long or the blades too short; for if the points can be

separated a quarter of an inch, nothing more is needed. If a pair of

bent scissors can also be obtained, they are extremely pleasant to work

with, and save much trouble.

[Illustration]

For arranging the objects under the microscope, there are no instruments

equal to those which are here engraved. They are nothing more than

ordinary needles stuck into the handles of camel’s-hair brushes. The

uppermost is made of the largest-sized darning-needle, and is useful for

making little holes, and similar purposes. The two next instruments are

the most generally useful, and several of each should be always at hand.

Nos. 4 and 5 are for special purposes; the former for holding tissues

aside, and the latter for lifting them up. The needles must not be

longer than those in the illustration, as they would otherwise be too

springy, and apt to tear the object instead of pulling or pushing it.

The bending is readily done in the flame of a spirit-lamp, or even of a

common candle; but in the latter case the needle is always covered with

soot, which must be wiped off before its shape can be seen. The

elasticity of the needles is lost by the operation, but is easily

restored by heating them red-hot, and plunging them immediately into

cold water. The end of the handle should be wrapped with thread, in

order to prevent it from splitting.

Pill-boxes of various sizes are of very great service to the

microscopist. We always have them arranged in “nests,” _i. e._ six or

seven inside each other, so that space is greatly economized, as long as

they are not in absolute use. All delicate objects should be placed in

separate boxes, and the predaceous insects must be treated in the same

manner, or they will certainly destroy one another, or, at all events,

inflict such injuries as will make them useless for microscopic

purposes.

[Illustration]

When the insects are to be killed on the spot, we employ another and a

very simple plan.

We take one of the old-fashioned wooden lucifer-match boxes, bore a hole

in the lid, and push through the hole a swan-quill or the barrel of one

of the swan-quill steel pens. A glass tube is still better, but is too

fragile. Beeswax is tightly worked into the junction of the tube with

the wood, so as to make it as nearly air-tight as possible. A cork

stopper is then cut to fit the tube. The accompanying illustration will

show the box completed. When this is finished, we take the

smallest-sized pill-box, bore a number of holes in it with a red-hot

needle, place a little piece of solid ammonia within it, and inclose it

in the lucifer-box. Its effects are almost instantaneous; for scarcely

has the insect touched the bottom of the box before it is helpless, and

in a very few moments it is quite dead, so powerful is ammonia towards

insects. The reader will of course understand that the pill-boxes must

never have been used for pills, and that the match-box must be carefully

cleaned before employing it in the microscopic service. Moreover, any

boxes that have been used for lepidopterous insects become useless,

inasmuch as the scales always fall from the wings, and cling to the

sides of the box, so as to mix with succeeding objects, and very much

puzzle the observer.

Aquatic and marine objects require bottles, and, as a general rule,

these bottles ought always to have wide mouths. Indeed, if there be no

shoulder at all, their purpose will be better served, as a small object

is very apt to be caught under the shoulder, and to give much trouble

before it can be removed without injury. Wide and short test-tubes

answer admirably for collecting; and it will always be advisable to have

a few small test-tubes ready fitted with corks, for the purpose of

isolating those specimens which might receive or cause injury by being

mixed with others.

To remove minute objects from one vessel into another is a very easy

process. Take a glass tube, mark off a portion about eight inches in

length, cut a little notch with a file, and bend it smartly, when it

will break neatly across, without leaving points or having the

regularity of its ends injured by gaps. Turn each end round and round in

the flame of the spirit-lamp, and you have an ordinary “pipette.” The

object of placing the ends of the tube in the flame is to render the

edges quite smooth and rounded.

Now mark off the same length of tube, and place the marked portion in

the flame, taking care to warm it well first, lest the sudden heat

should crack the glass. Keep it continually turning between the fingers,

and when it is quite soft, and of a fine red heat, draw the hands

smartly apart, and you will produce a couple of tubes tapering to very

fine points. Break off the tapering portions at any convenient point,

round the edges as before, and you will then have pipettes suitable for

small objects. As there are many specimens, especially the smaller

animalculæ, which have a habit of retiring into the remotest corner, it

is necessary to bend another pipette, so as to follow them. For our own

part, we prefer the pipette to be bent nearly to a right angle.

The mode of using these simple instruments is as follows:--Place the

forefinger or thumb firmly on the large end, and push the point under

water. When the opening is close to the sought-for object, lift the

finger suddenly, and admit the air into the tube. The water will

immediately rush in at the lower end, and if the orifice has been

properly directed, will carry the object into the tube. The finger is

again applied to the mouth of the tube, and the object can be then

carried off.

As with the pocket-lens almost every object is to be viewed by means of

direct light, the young observer will find himself much aided by a

suitable background. Any small object, such as a minute insect, a seed,

or a hair, becomes very indistinct if held up against the light, or even

when viewed against a broken background of trees, houses, or herbage.

The simplest plan of securing a proper background is to take a disc of

ivory, bone, or even of white cardboard, and to blacken one side of it.

The black paint which is used for this purpose must be without gloss,

and have what is called a “dead” surface. Ink answers very well for the

purpose, and so does ivory-black; but Indian ink is too glossy to be

serviceable.

To procure specimens from the water is a matter of some difficulty if

managed badly, but easy enough when the collector knows his business. It

is of course needful to attach the collecting vessel to the end of a

rod, and to plunge it into the spots which look most favourable. Now

even so simple a matter as this requires some little care, if the young

microscopist really wishes to obtain the best specimens. A common

walking-stick will answer most purposes; but the most efficient rod for

the purpose is one of the common walking-stick fishing-rods without the

top joint, as it can be carried without attracting attention, and can be

lengthened at will by adding the different joints.

[Illustration]

Many methods have been proposed by which the vessel is to be attached to

the rod; but that which I am about to describe is certainly the simplest

and most effective that I have tried. Get a piece of gutta-percha

tubing, just large enough to be slipped on the end of the rod or stick;

mark off an inch or so, and cut the tube nearly through, as at _a_ in

Fig. 1. Now cut it away longitudinally, so that a long tongue of

gutta-percha is left, as at _b_, and the instrument is completed.

Its application is as simple as its structure. Bend the tongue over, so

as to form a loop, and push the end through the short tube. Slip the

neck of the bottle into the loop, and draw the tongue until it is

tolerably tight. Push the end of the stick into the tube, taking care to

hold the tongue firmly in its place, and the vessel will then be

fastened at right angles to the stick.

The whole arrangement can be seen in Fig. 2, where _a_ represents the

gutta-percha tube, _b_ the tongue, _c_ the stick, and _d_ the vessel.

The method of collecting by means of this instrument is as

follows:--Immerse the vessel in the water, with the mouth downwards, so

that no water may enter. Push it gently towards the spot which is to be

investigated, move it about a little, so as to cause a disturbance, and

then turn the vessel with its mouth upwards. Water will instantly rush

in, carrying with it the objects which are to be examined. The contents

of the vessel may then be transferred to the large bottle, and another

dip made. Confervoid growths, especially those which accumulate in a

kind of scum on the surface, should be obtained very quietly, without

previous disturbance of the water.

After the pond or stream or ditch has been well searched, the bottle

should be roughly examined, by means of a pocket-lens, and the contents

sorted into the smaller tubes, as has already been mentioned. This

precaution is especially needful when any of the minute crustacea called

Entomostraca are captured, as they are most voracious beings, and will

make sad havoc among other specimens, unless they are placed in separate

bottles. They are mostly large enough to be detected with the naked eye,

and look something like little fleas, as they move along.

As the Entomostraca cast their shells repeatedly during their lives,

some species performing this operation every two days, a beautiful

series of objects can be obtained by gathering the cast shells, and

preparing them for the microscope, according to the directions that will

be found in the following pages. These shells are peculiarly valuable,

as they retain the chief external characteristics of the creature to

which they belonged, the limbs, plumes, and even the delicate bristles

being preserved entire. It is in the power of the microscopist to retard

or hasten the change of shell, heat and light aiding development, and

cold and darkness retarding it. The remarkable “ephippium,” or saddle,

which is found on the backs of the Daphnia, the Moina, and other

Entomostraca, and which is used as a receptacle for eggs, should be

searched for and preserved.

A very thin and very flat bottle is a most useful assistance in

detecting the character of any unknown object, especially if it be

living. Such a bottle may easily be made by heating one of the small

test-tubes in the spirit-lamp until it is of a glowing red heat, and

then pressing the sides together. Some little neatness is required in

this process, as an unskilful operator is apt to press the sides

unequally, and to leave a bulging projection at the end.

Should a higher power be required than is furnished by the pocket-lens,

a “Coddington” lens is the very best that can be obtained. In general

shape it resembles the well-known “Stanhope” lens; but the latter is so

very inferior an article, that it ought never to be purchased. The two

glasses can easily be distinguished by the shape of the ends; those of

the Coddington being alike, while in the Stanhope one is much more

convex than the other.

At first the young observer generally finds some difficulty in arranging

this lens, so as to hit off the focus exactly; but if he adopts the

following plan, he will soon handle a Coddington as easily as an

ordinary pocket-lens. The object should be held in the left hand and the

glass in the right. Let the wrists be placed firmly against each other,

and the lens brought as close as possible to the object, without quite

touching it. Now bring the eye to the lens, taking care not to disturb

the arrangement, and then gradually draw the object away from the lens.

The moment that the proper focus is obtained the object will be seen

with beautiful clearness, and by drawing the object from the lens,

instead of approaching the lens to the object, there is no danger of

injuring the one or the other by contact.

The great advantages of the Coddington are the exceeding clearness with

which it shows the object, the perfect definition of every line, its

achromatic character, and its freedom from colours, and the flatness of

the “field;” so that the circumference is defined as perfectly as the

centre. It can now be obtained very cheaply at any of our microscopical

opticians, and should always be mounted on a tolerably long handle.

THE COMPOUND MICROSCOPE.

We have already described the simpler forms of magnifying instruments,

together with the best method of using them. We now purpose to describe

the more complicated instrument called the compound microscope, and

hints will be given as to the best method of making preparations for it.

The great distinction between the simple and compound microscope is,

that whereas the former instrument magnifies the object, the latter

magnifies the magnified image of the object. In the least elaborate form

of this instrument there are two glasses, one at each end of a tube, the

small glass magnifying the object, and being therefore called the

“object glass,” while the other, which magnifies the image of the

object, is placed next to the eye, and is therefore termed the

“eye-glass.” In practice, however, this arrangement is found to be so

extremely defective, that the instrument was quite useless, except as an

experimental toy; for the two enemies of the optician, chromatic and

spherical aberration, prevailed so exceedingly, that every object

appeared as if surrounded with prismatic colours, and every line was

blurred and indistinct.

In this uncertain state the compound microscope remained for many years,

its superb capabilities being scarcely recognised. The chief fault was

thought to be in the material of which the object-glass was made, and

for a long series of years all experiments were conducted with a view to

an improvement in this respect. When, however, the diamond had been

employed as an object-glass, and had failed equally with those of less

costly material, attention was directed to the right point--namely, the

arrangement of the different glasses,--and at length opticians succeeded

in obtaining a pitch of excellence which can be almost termed

perfection. It would be impossible to describe the method which is

employed for this purpose, and it must suffice to say that the principle

is that of playing off one defect against another, and so making them

mutually correct their errors.

The magnifying powers of the compound microscope can be very great, and

it is therefore necessary that extreme care should be taken in its

manipulation. It will be possible for a clumsy person to do more damage

to a good instrument in three minutes than can be repaired in as many

weeks.

Before proceeding to the management of the microscope and the

construction of the “slides,” we will briefly describe one or two chief

forms of the compound microscope.

[Illustration]

The accompanying illustration represents the simplest form of the

compound microscope as at present made. It consists of a stand and a

sliding tube, in which are set the glasses which magnify the object and

its image. At the top is the tube, which is capable of being slid up and

down in the shoulder of the stand, so as to obtain the proper focus.

Above is seen the eye-glass; and the object-glass is shown at the bottom

of the tube. Below the object-glass is the “stage” on which the object

to be magnified is laid; and lowest of all is a mirror, which serves to

reflect the light upwards through the object, and which can be turned by

means of the knobs at the sides. The object-glass is composed of two

pieces, which can readily be separated. If both are used, sufficient

magnifying power is gained to show the scales on a butterfly’s wing and

similar minute objects; while, if one is removed, the object is not

magnified to so great an extent, but a larger portion can be seen, and

the definition is clearer. The cost of this instrument, together with a

few accessories, is half-a-guinea.

There is another microscope constructed on the same principle, which is

a very superior instrument, though it does not at first sight present

any remarkable difference. It possesses, however, four times the

magnifying power of that which has just been mentioned. Instead of two

magnifiers, there are four, and several subsidiary articles are sent

with it,--such as a condenser, a live box, an aquatic box, and half a

dozen slides ready prepared. This instrument costs one sovereign.

[Illustration]

But if the reader can by any possibility afford it, let us advise him in

the strongest terms to devote three guineas to the purpose, and get a

really good instrument. For this small sum a microscope may now be

obtained which could not have been purchased for twenty times three

guineas only a few years ago. One of these beautiful instruments is seen

in the accompanying illustration; in which may be seen the tube, with

its eye-piece and object-glass, and the stand, containing the stage and

the mirror. The arrangement, however, is very different; for the focus

is not obtained by sliding the tube up and down, but by turning the

large milled heads which we see on a level with the stage, and which

raise or depress the tube by means of a rack and pinion. As an extremely

high power can be used with this instrument, a still finer adjustment is

required, so as to obtain a very accurate focus. This is seen on the

front of the tube. The reader will notice that the microscope can be

inclined backwards, for it is so made that it can be set to any angle

which may best suit the observer. The value of this arrangement is very

great, as it permits the observer to sit at his ease in a chair, without

being forced to crane his neck over the microscope, and look

perpendicularly down. Another advantage attending this arrangement is

that the secretions which lubricate the eye do not interrupt the vision,

as is apt to be the case when looking directly downwards.

The mirror, too, can be turned in any direction, and its distance from

the stage lessened or increased by means of a draw-tube. Three different

powers are supplied with this microscope, together with a live-box,

dissecting and stage forceps, &c.; and the whole is made so as to admit

of additional apparatus. The microscope fits into a neat square box, in

which is plenty of room for various articles which will presently be

described. These three microscopes can be obtained from Messrs. Baker,

244, High Holborn; and we mention them, not because we wish to make any

invidious distinctions between the many excellent opticians who now make

microscopes, but because we happen to have used Messrs. Baker’s

instruments for some years, and can bear practical testimony to their

performance.

Another three-guinea microscope ought, however, to be mentioned. It is

the Society of Arts microscope, which is made by Messrs. Field,

opticians, of Birmingham. In form it closely resembles the instrument

which has just been mentioned, but differs in some of the details, as it

possesses a “diaphragm-plate” under the stage for regulating the

admission of light, and, instead of three object-glasses and one

eye-piece, has two object-glasses and two eye-pieces. Dr. Carpenter

mentions that, up to 1861, no less than eighteen hundred of these

microscopes had been sold. To this instrument the medal of the Society

of Arts was awarded.

Either of these microscopes affords all that an ordinary observer is

likely to need; and if he adds a few articles of supplementary

apparatus, he will find himself possessed of a microscope that will

serve all purposes except scientific controversy.

Presuming that the reader has supplied himself with one or other of the

compound microscopes, we will proceed to show the method of using them.

The manipulation of a compound microscope is not so easy as it looks.

The possessor of a really good instrument may fail hopelessly in his

attempts to see a single object. Now, there are three essential points

which a microscopist must attend to,--namely, the correct focus, the

proper light, and the preparation of the object. Of these the focus is

of course the most important, and can be best obtained as follows:--

Lay the object on the stage of the microscope, so as to get its centre

exactly under the centre of the object-glass, and illuminate it as you

best can. Put on the _lowest_ power, and, without looking through the

tube, lower the object-glass until it nearly touches the object. Now

look through the tube, and raise the object-glass gradually from the

object, until the right focus is obtained. The reason for taking these

precautions is, that if you look through the tube and lower it upon the

object, you will in all probability push the glass against the object,

and damage either the one or the other. When you have thus learned the

focus of the lowest power, add another, and repeat the process; and so

on until you have made out the focus of each object-glass. If you have

more than one eye-piece, try them both with each object-glass.

The proper light is our next point, and upon it rests the chief beauty

of the effect. The light which will suit one object will not suit

another, and even the same object should be examined under every variety

of light. Some objects are best shown when the light is thrown _upon_

them from above, and others when it is thrown _through_ them from below.

Again, the direction of the light is of vast importance; for it will

easily be seen that an oblique light will exhibit minute projections by

throwing a shadow on one side and brilliancy on the other, while a

vertical illumination would fail to show them. On the same principle,

one object will be shown better with the light in front, and another

when it is on one side.

[Illustration]

One of the most effective means of attaining this object is by using the

“bull’s-eye condenser,” which is sometimes fixed to the stage, but is

usually detached, as represented in the illustration. As the upright

stem is telescopic, the glass can be raised to a considerable height,

while the joint and sliding-rod permit the lens to be applied at any

angle which promises the most brilliant light.

As for the kind of light that is employed, there is nothing which equals

that of a white cloud; but as such clouds are rare, and are at the best

extremely transient, and can only be seen by day, various artificial

methods of illumination have been invented. Novices generally think that

when the sky is bright and blue they will be very successful in their

illumination, and feel grievously disappointed at finding that they

obtained much more light from the clouds, whose disappearance they had

anxiously been watching. Finding that the blue sky gives scarcely any

light at all, they rush to the other extreme, turn the mirror towards

the sun, and pour such a blaze of light upon the object, that the eye is

blinded by the scintillating refulgence, and the object is often

injured, because the mirror is capable of reflecting heat as well as

light.

In the daytime there is nothing better than the “white-cloud

illuminator,” which is made easily enough by means of plaster of Paris.

A sheet of thin white paper fastened against a window-pane is also

useful; and the simple plan of dabbing the glass with putty will have a

beneficial effect in softening the light, when the window has a southern

aspect. In default of these conveniences, it will be often sufficient to

fix a piece of white letter-paper over the mirror, or even to dull its

surface with wax. At all events, he who aspires to be a true

microscopist must be ready with expedients, and if he finds himself in a

difficulty, he must summarily invent a method of obviating it.

At night a lamp is necessary; candles are useless, because they have two

faults--they flicker, and they become lower as they burn. The latter

defect can be cured by using a candle-lamp, but no arrangement will cure

the flame of flickering; it is peculiarly trying to the eyes, and

destructive of accurate definition. An ordinary moderator lamp answers

pretty well, and a small one is even better for the microscopist than

one of large dimensions. The chief drawback to the moderator lamp is,

that the flame cannot be elevated or lowered, so that the only way to

procure a light at a higher elevation, is to stand the lamp on a block

of wood or a book. Small lamps are, however, made expressly for the

microscope, and, if possible, should be procured, and used for no other

purpose, and intrusted to no other hands.

If you want a really brilliant, clear, white light, you must trim the

lamp yourself. A small piece of pale blue or neutral-tint glass,

interposed between the lamp and the microscope, has a wonderful effect

in diminishing the yellow hue which belongs more or less to all

artificial lights which are produced by the combustion of oil or fat. We

have no doubt but that in a few years we shall be rid of the clumsy and

dirty machines that we call lamps, and have substituted for them the

pure brilliancy of the electric light.

Whatever lamp you use, a shade is absolutely necessary, in order to

defend the eyes. Let me here warn my young readers, that they cannot be

too careful of their eyes. In the exuberance of youthful strength and

health we are too apt to treat our eyes as unceremoniously as our

digestion, and in later years we awake to unavailing repentance.

[Illustration]

Many shades can be purchased; but it is far better to make your own

after the shape here exhibited. They are not pretty to look at, but

they save the eyes better than any other form, and whether for reading,

writing, or microscopic work, you should use no other. The peculiar

merit of them consists in the fact that the light is thrown on the spot

where it is wanted, and is cut off from everything except that spot.

Another point which calls for extreme attention is the perfect

cleanliness of the glasses. It is astonishing how a tiny dust-mote, or

the least condensation of damp, will diminish the powers of the

microscope, and how often the instrument is blamed for indistinctness,

when the real fault lies in the carelessness of the operator. Even when

the greatest care is taken, dust is sure to settle on the glasses,

especially on the eye-piece, and before using the microscope the glasses

ought to be carefully examined. Never wipe them with an ordinary

handkerchief, but get a piece of new wash-leather; beat it well until no

dust issues from it, and then put it into a box, with a tightly-fitting

cover. Use this, and nothing else, for cleaning the glasses, and you

will avoid those horrid scratches with which the eye-glass and

object-glass of careless operators are always disfigured.

Moisture is very apt to condense on the glasses and to ruin their

clearness. If the microscope be brought from a cold into a warm room,

the glasses will be instantly covered with moisture, just as the outside

of a tumbler of cold water is always covered with fine dew when brought

into a warm room. The microscope should therefore be kept at least an

hour in the room wherein it is to be used, so that the instrument and

the atmosphere may be of the same temperature. You should make the

microscope a trifle warmer than the surrounding atmosphere, and so avoid

all danger of condensation. When changing the object-glass or eye-piece,

always keep the hand as far away from the glass as possible, and

manipulate with the tip of the forefinger and thumb. The human skin

always gives out so much exhalation, that even when the hand is cold the

glasses will be dimmed; and it is a peculiarity of such moisture, that

it adheres to the glasses with great pertinacity, and does not evaporate

like the dew which is condensed from the atmosphere.

In order to insure perfect success in this important particular, the

young microscopist will do well to get the optician from whom he

purchased his instrument to explain its construction, and to give him a

lesson or two in the art of taking it to pieces and putting it together

again; for unless each glass can be separately cleaned, no one can be

quite sure that the instrument will perform as it ought to do. The best

method of ascertaining whether it is quite clean is to throw the light

upwards by means of the mirror, and then to turn the eye-piece slowly

round. If any dust or moisture has collected either upon the eye-glass

or the “field-glass,” which forms the second lens of the eye-piece, it

will be immediately detected. Turning the object-glass will in a similar

manner detect impurities upon its surface.

We will now proceed to the manner in which objects are examined.

Suppose, for example, that we take a buttercup-leaf, because it can be

found at almost any time of the year. Place a piece of glass on the

stage, lay the leaf on it, put on the lowest power, set the focus, and

then look at the leaf. You will probably be disappointed, and see

nothing but a confused mass of undulating dark green, like a green

carpet thrown carelessly on the ground, and seen in the dim twilight.

Two points are now needed; the first being to get the leaf flat, so as

to avoid the undulation, and the second being to throw a proper light

upon it.

Take out the leaf, and, instead of laying it entire under the

microscope, select the flattest part, and cut it out with scissors. A

piece the size of a silver penny will be amply large enough. Lay this

piece on the glass, get the focus afresh, and then look through the

microscope. The leaf will now appear much more regular, and will be seen

as a rough surface, mottled with white and traversed by pink and green

ridges, which are the large and small nervures. By means of a mirror or

the condenser throw a brighter light upon it, and it will be seen to be

covered with a slight roughness, the nature of which cannot be clearly

ascertained; then add the next highest power, and try if the structure

of that roughness can be made out. Curiously enough, although the

magnifying power has been more than doubled, the roughness has much the

same appearance as before; so that we must try another plan, and look at

the leaf edgeways.

Take the piece of leaf in the stage-forceps, but _do not touch it with

your hand_; fix the forceps on the stage and turn the leaf so that it

presents its edge to the object glass. Get your focus, and you will now

see the cut edge of the leaf, and will at once distinguish its

structure. On either side may be seen the upper and lower cuticle, and

in the centre the soft green substance, or “parenchyma,” as it is

called. From the cuticle project a number of short hairs, and when the

focus is accurately obtained, the cause of the roughness will be seen in

a vast number of minute projections, which are, in fact, identical in

structure with the hairs, though not so well developed. The

under-cuticle of the leaf is much more interesting than the upper.

[Illustration]

Now change the illumination, and, instead of throwing the light upon the

object from above, turn the mirror so as to direct it through the object

from below. No apparent result will follow, because the leaf is so thick

and opaque that the light cannot pass through it. Hold the leaf

horizontally, and, by means of the stage-forceps, rip it smartly across,

and if you do this rightly, you will find that the two cuticles are

partly separated, so as to allow either to be examined separately. At

first the leaf will most probably be torn along one of the large

nervures, so that the cuticles are not perfectly separated. Never mind

failure, but try again; and you are sure, after a few efforts, to hit

upon the right method of tearing the leaf.

[Illustration]

One of the most useful capabilities of the “live-box” is now shown. As

may be seen by the figure and section, it consists of an inner tube with

a thick glass, and an outer tube with a thin glass. The outer tube can

be taken off, water or any other substance laid on the thick glass, and

then the outer tube or cover is slid down upon it until the object is

pressed flatly between the two glasses. When you have succeeded in

getting a convenient slip of the leaf, lay it on the thick glass of the

inner tube, and put a drop of water on it. Put on the cover, and push it

down until the piece of leaf is pressed flat, without being squeezed.

Now look through the microscope, and you will see a beautiful sight,

showing how much there is in a despised leaf, which we daily tread under

foot.

[Illustration]

The cells of which the cuticle is chiefly composed are seen in many a

waving outline, while at their points of junction are placed the

remarkable contrivances called “stomata,” or mouths, which are the

apertures through which the atmosphere is enabled to penetrate into the

interior of the leaf. The two semilunar cells at the sides of the

opening may be considered as lips, which open and close according as the

plant needs the air or not. The numerous dots which are seen upon the

leaf are of a vivid green colour, and it is to their presence that the

leaf owes its hue.

We have given these details because they are applicable to the

examination of all leaves and petals, and show the young observer the

method which is to be adopted when looking for the first time at a

strange object.

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