_Compound Forces.--The Composition and Resolution of
Motion.--Rotatory Motion.--The Revolving Watch-glass.--The
Sling.--The Centrifugal and Centripetal Forces.--Theory of
Projectiles.--A Geological conversation between Mr. Seymour and
the Vicar._
On the following morning, Mr. Seymour proceeded to explain the nature
of “COMPOUND FORCES.” The young party having assembled as usual, their
father commenced his lecture by reminding his auditors, that the motion
of a body actuated by a single force was always in a right line, and in
the direction in which it received the impulse.
“Do you mean to say, papa, that a single force can never make a body
move round, or in a crooked direction; if so, how is it that my ball,
or marble, will frequently run along the ground in a curved direction?
Indeed, I always find it very difficult to make it go straight.”
“Depend upon it, my dear, whenever the direction of a moving body
deviates from a straight line, it has been influenced by some second
force.”
“Then I suppose that, whenever my marble runs in a curved line, there
must be some second force to make it do so.”
“Undoubtedly; the inequality of the ground may give it a new direction;
which, when combined with the original force which it received from
your hand, will fully explain the irregularity of its course. It is to
the consideration of such compound motion that I am now desirous of
directing your attention: the subject is termed the “COMPOSITION OF
FORCES.” Here is a block of wood, with two strings, as you may
perceive, affixed to it: do you take hold of one of these strings,
Louisa; and you, Tom, of the other. That is right. Now place the block
at one of the corners or _angles_ of the table: and while Tom draws it
along one of its sides, do you, Louisa, at the same time, draw it along
the other.”
The children obeyed their father’s directions.
[Illustration: A piece of wood with two strings attached to it, and two
hands pulling the strings in diagonal directions.]
“See!” said Mr. Seymour, “the block obeys neither of the strings, but
picks out for itself a path which is intermediate. Can you tell me,
Tom, the exact direction which it takes?”
“If we consider this table as a parallelogram, I should say, that the
block described the diagonal.”
“Well said, my boy; the ablest mathematician could not have given a
more correct answer. The block was actuated by two forces at the same
time; and, since it could not move in two directions at once, it moved
under the _compound_ force, in a mean or diagonal direction,
proportioned to the influence of the joint forces acting upon it. You
will, therefore, be pleased to remember, it is a general law, that
where a body is actuated by two forces at the same time, whose
directions are inclined to each other, at any angle whatever, it will
not obey either of them, but move along the diagonal. In determining,
therefore, the course which a body will describe under the influence of
two such forces, we have nothing more to do than to draw lines which
show the direction and quantity of the two forces, and then to complete
the parallelogram by parallel lines, and its diagonal will be the path
of the body. I have here a diagram which may render the subject more
intelligible. Suppose the ball B were, at the same moment, struck by
two forces X and Y in the directions B A and B D. It is evident that
the ball would not obey either of such forces, but would move along the
oblique or diagonal line B C.”
[Illustration: Fig. 4. Force diagram for a ball moving in a diagonal
direction.]
“But,” said Tom, “why have you drawn the line B D so much longer than
B A?”
“I am glad you have asked that question. Lines are intended, not only
to represent the direction, but the _momenta_, or quantities of the
forces: the line B D is, as you observe, twice as long as B A; it
consequently denotes that the force Y acting in the direction B D, is
twice as great as the force X acting in the direction B A. Having
learned the direction which the body will take when influenced by joint
forces of this kind, can you tell me the relative time which it would
require for the performance of its diagonal journey?”
Tom hesitated; and Mr. Seymour relieved his embarrassment by informing
him, that it would pass along the diagonal in exactly the same space of
time that it would have required to traverse either of the sides of the
parallelogram, had but one force been applied. Thus, the ball B would
reach C in the same time that the force X would have sent it to A, or
the force Y to D. “I will endeavour to prove this fact beyond all
doubt. It is, I think, evident, that the force which acts in the
direction B A can neither accelerate nor retard the approach of the
body to the line D C, which is parallel to it; hence it will arrive at
C in the same time that it would have done had no motion been
communicated to it in the direction B A. In like manner, the motion in
the direction B D can neither make the body approach to nor recede from
A C; and it therefore follows, that, in consequence of the two motions,
the body will be found both in A C and C D, and will therefore be found
in C, the point of intersection.”
Louisa seemed to express by her looks the irksomeness of such
demonstrations; and which did not pass unobserved.
“This may appear tedious and uninteresting,” said Mr. Seymour, “but the
information is absolutely essential to our future progress: if you
would reap, you must sow.”
Tom and Louisa both expressed themselves willing to receive whatever
instruction their father might consider necessary; and they farther
declared, that they understood the demonstration he had just offered
them.
“Is it not then evident,” proceeded Mr. Seymour, “that the composition
of forces must always be attended with loss of power; since the
diagonal of a parallelogram can never, under any circumstances, be
equal to two of its sides? and is it not also evident, that the length
of the diagonal must diminish as the angles of the sides increase: so
that the more acute the angle at which the forces act, the less must be
the loss by composition? But I shall be better able to explain this law
by a diagram. If B A, A C be the sides of a parallelogram, representing
the direction of two forces, and A D the diagonal path of the body, is
it not evident that the line A D will shorten as the angle B A C
increases?”
[Illustration: Fig. 5. Three parallelograms, beginning with a square
and ending with a narrow diamond, all sharing one side.]
“We see that at once,” cried Tom, “from the diagram before us.”
[Illustration: Fig. 6. A square and a rectangle with a common diagonal.]
“Then we will proceed to another fact connected with the same subject.
Look at this diagram; is not the diagonal A D common to both the
parallelograms inscribed about it, viz. of A B C D, and A E F D?”
“To be sure it is.”
“Then it is equally clear, that a body may be made to traverse the same
path A D, by any pair of forces represented by the adjacent sides of
either of such parallelograms.”
“Undoubtedly.”
“I request you to keep that fact in your recollection.”
“I have now to inform you,” continued he, “that a single force may be
resolved into any number of forces, and may, in fact, be regarded as
compounded of innumerable oblique ones. In order, however, to render
this fact more intelligible, I must refer you to fig. 6, from which it
will appear that the motion of a body, along the line A D, will be the
same whether it arise from one single force acting in that direction,
or from two forces impressed upon it in the directions A B, A C, or in
those of A E, A F; and, consequently, although the motion may, in
reality, be the effect of a single force, yet it may be considered as
compounded of two or more in other directions, since the very same
motion would arise from such a composition.”
Tom acknowledged the truth of this statement; and Mr. Seymour assured
him, that, when they came to play at ball and marbles, he should be
able to give him a practical demonstration of the fact; for he would
show him, that whenever a body strikes a surface obliquely, or in an
inclined direction, such a _resolution of force_ will actually take
place: “and now, Tom,” said his father, “give me a marble; for I wish
to explain the reason why it turns round, or revolves on its axis, as
it proceeds forward.”
“I suppose,” said Tom, “it depends upon the action which I give to it
by my thumb and finger when I shoot it out of my hand.”
“You are, undoubtedly, capable of thus giving to your marble a certain
_spinning_ motion, the effect of which we shall have to consider
hereafter; but I fancy you would be greatly puzzled to make it proceed
without revolving, give it what impulse you might by your hand.”
“I have sometimes tried,” said Tom, “to make it do so by pushing it
along with a flat ruler, but it always _rolled_ in spite of me.”
[Illustration: Fig. 7. Diagram for marble’s motion.]
“Then it is clear, from your own experiment, that its rotation cannot
arise from the cause you would assign to it. If you will attend to this
diagram,” continued his father, “I will endeavour to explain the
operation. It is evident that, as the marble moves along the ground
B D, the motion of the point B will be retarded by the resistance
occasioned by its rubbing on the ground; while the point C, which does
not meet with any such resistance, is carried forward without
opposition, and it consequently must move faster than the point B; but
since all the parts of the marble cohere or stick together, the point C
cannot move faster than B, unless the marble revolves from C to E; and
as the several points of the marble which are successively applied to
the floor are retarded in their motion, while the opposite points move
freely, the marble during its progressive motion must continue to
revolve.”
“But you said, papa, that whenever a body moved in any direction,
except that of a straight line, it must have been acted upon by more
than one force; and yet the marble not only runs along the ground, but
turns round; at the same time, by the simple force of my hand.”
“The revolution of the marble, my dear boy, is brought about by no less
than three forces: look attentively at the diagram, and you will easily
comprehend my explanation. There is, in the first place, the
rectilinear motion given to it by your hand; then there is the friction
of the ground: since, however, this latter acts in a contrary
direction, it merely tends to lessen or counteract the velocity with
which the under-surface proceeds, and consequently to give a
relatively-increased progressive motion to its upper part; then comes
that force by which its several parts cohere, and which may be
represented by C H; so that the two forces producing the revolution of
the point C, are justly expressed by the lines C G, C H: but these are
in the direction of the two sides of a parallelogram, the point will
therefore move along the diagonal C E. I have here a toy for you, which
will serve to explain still farther the causes of rotation to which I
have alluded.” Mr. Seymour produced a watch-glass, in the hollow of
which stood a dancing-figure of thin card, as here represented.
[Illustration: Toy man standing on the flat part of a convex piece of
glass.]
He placed it upon a black japanned waiter,[16] which he held in an
inclined position, when it immediately slided down the inclined plane,
as might have been expected. He next let fall a drop of water upon the
waiter, and placed the watch-glass in it. Under this new arrangement,
instead of sliding, the watch-glass began to revolve as soon as an
inclination was given to the surface; and it continued to revolve with
an accelerated velocity, obeying the inclination and position of the
plane, as directed by the hand of the operator.
“What a very pretty effect is produced by the rapid revolution of the
figure!” observed Louisa.
“Its use in the arrangement,” said her father, “is to render the
accelerated motion more obvious.”
“I perceive it revolves faster and faster, or, I suppose I ought to
say, with an accelerated velocity,” said Tom.
“Certainly,” answered Mr. Seymour; “whenever a force continues to act,
the motion produced by it must be accelerated for the reason already
given you[17]--but let me explain the operation of the drop of water,
which, as you have just seen, converted the sliding into the revolving
motion. In the first place, in consequence of the cohesion of the water
to the two surfaces, a new force was introduced, by which an unequal
degree of resistance was imparted to different portions of that part of
the watch-glass in contact with the plane, and, consequently, in its
effort to slide down, it necessarily revolved. Now, if you will
attentively observe the change of figure which the drop of water
undergoes during the revolution of the glass, you will perceive a
species of vortex; a film of water, by capillary action, is drawn to
the foremost portion of the glass, while, by the centrifugal force, a
body of water is thrown under the hinder part of it; the effect of both
these actions is to accelerate the rotatory motion.
“I shall now dismiss the subject for the present, but on some future
occasion I shall probably revert to it; for it may be made to afford a
simple illustration of the rotatory and progressive motions of the
earth round the sun; and it may also give us the means of producing
some optical effects of a very curious kind.”(15)
Mrs. Seymour here suggested that, as it was past one o’clock, the
children should be dismissed to their more active sports in the garden.
“We will instantly proceed to the lawn,” replied Mr. Seymour, “and Tom
may try his skill with the _sling_; an amusement which I have provided
as a reward for his industry, and which will, at the same time, convey
some farther information concerning the nature of those forces we have
been just considering. The sling,” continued his father, as he advanced
upon the lawn, “consists, as you perceive, of a leathern thong,
broadest in the middle, and tapering off gradually towards both ends.
To each extremity is affixed a piece of string. I shall now place a
stone in the broad part of the leather, and introduce my middle finger
into the loop formed in one of the strings, and hold the other
extremity between my fore-finger and thumb.”
He then whirled it round, and when it had gained sufficient impetus, he
let go his hold of the string, and the stone instantly shot forth with
amazing velocity.
“See! see! there it goes,” exclaimed Tom; “to what a height it
ascended!”
“And to what a distance has it been projected!” observed Louisa, who
had attentively watched its descent.
“Now, Tom,” said his father, “can you explain the operation you have
just witnessed?”
“Not exactly, papa.”
“Then attend to me. Have you not learned that circular motion is always
the result of two forces?”
“Undoubtedly,” replied Tom; “of one force which attracts it to the
centre around which it moves, and of another which impels it to move
off in a right line.”
“Certainly; the former of these forces is, therefore, termed the
_centripetal_, because it draws the body towards the centre, while the
latter is called the _centrifugal_ force, since its influence disposes
the body to fly off from the centre. In circular motion, these two
forces constantly balance each other; otherwise it is evident that the
revolving body must either approach the centre or recede from it,
according as the one or the other prevailed. When I whirled round the
sling, I imparted a projectile force to the stone, but it was prevented
from flying off in consequence of the counteracting or _centripetal_
force of the string; but the moment I let go my hold of this, the stone
flew off in a right line: having been released from confinement to the
fixed or central point, it was acted upon by one force only, and motion
produced by a single force is, as you have just stated, always in a
right line.”
“But,” observed Louisa, “the stone did not proceed in a straight, but
in a curved line: I watched its direction from the moment it left the
sling till it fell to the ground.”
“You are perfectly correct,” replied Mr. Seymour, “it described a
curve, which is called a _parabola_; but that was owing to the
influence of a new force which came into play, viz. that of gravity,
the effect of which I shall have to explain hereafter.”
“I cannot understand,” said Tom, “why the stone should not have fallen
out of the sling when you whirled it round over your head.”
“Because, my dear, it was acted upon by the _centrifugal_ force, which
counteracted that of gravity: but I will render this fact more evident,
by a very simple and beautiful experiment. I have here a wine-glass,
around the rim of which I shall attach a piece of string so as to
enable me to whirl it round. I will now fill it with water, and
although during one part of its revolution it will be actually
inverted, you will find that I shall not spill a single drop of water.”
Mr. Seymour then whirled round the glass, and the young party were
delighted with the confirmation thus afforded to their father’s
statement.
“I see,” said Tom, “how it happened: when the glass was inverted the
water could not fall out, because it was influenced by the centrifugal
force which opposed gravity.”
“Exactly. Have you ever observed what happens during the trundling of a
mop? The threads which compose it fly off from the centre, but being
confined to it at one end they cannot part from it: while the water
which they contain being unconfined, is thrown off in right lines.”
“I have certainly observed what you state,” said Louisa; “the water
flies off in all directions from the mop.”
“Yes,” added Tom, “the water was not acted upon by the _centripetal_
force as the threads were, and consequently, there was nothing to check
the _centrifugal_ force, which carried the water off in a straight line
from the centre.”
“You are not quite correct,” said Mr. Seymour; “the water does not fly
off in a right line from the centre, but in a right line in the
direction in which it was moving at the instant of its release; the
line which a body will always describe under such circumstances, is
called a _tangent_, because it _touches_ the circumference of the
circle, and forms a right-angle with a line drawn from that point of
the circumference to the centre: but I will render this subject more
intelligible by a diagram.
“Suppose a body, revolving in the circle, was liberated at _a_, it
would fly off in the direction _ab_; if at _c_, in that of _cd_; and if
at _e_, in that of _ef_; and so on. Now, if you draw lines from these
several points to the centre of the circle, you will perceive that such
lines will form, in each case, a right-angle. In the experiment which
you have just witnessed, the surface of the water must have formed,
during its revolution, a right-angle with the string, and consequently
could not have fallen out of the wine-glass. A knowledge of this law,”
continued Mr. Seymour, “will explain many appearances which, although
familiar, I dare say, have never been understood by you. You may
remember accompanying me to the pottery, to see the operation of the
turning-lathe; it was owing to the centrifugal force produced by the
rotation of the wheel, that the clay, under a gentle pressure, swelled
out so regularly; from a similar cause, the flour is thrown out of the
revolving mill as fast as it is ground; and I shall presently show you
that you are indebted to this same force for the spinning of your top
and the trundling of your hoop. But let us quit this subject for the
present, and pursue the stone in its course after it is liberated from
the sling. Louisa has justly observed that it described a curve; can
you explain why it should deviate from a straight line?”
[Illustration: Fig. 8. Diagram for centrifugal force.]
“Let me see,” said Tom, thoughtfully; “it would be acted upon by two
forces, one carrying it forward in a right line, the other bringing it
to the earth; it would, therefore, not obey either, but describe a
diagonal: but why that diagonal should be a curve I cannot exactly
explain.”
“Then I will give you the reason,” said his father. “A stone projected
into the air is acted upon by no less than three forces; the force of
projection, which is communicated to it by the hand or the sling; the
resistance of the air through which it passes, and which diminishes its
velocity without changing its direction; and the force of gravity,
which ultimately brings it to the ground. Now, since the power of
gravity and the resistance of the air will always be greater than any
force of projection we can give a body, the latter must be gradually
overcome, and the body brought to the ground; but the stronger the
projectile force, the longer will those powers be in subduing it, and
the farther will the body go before it falls. A shot fired from a
cannon, for instance, will go much farther than a stone thrown from
your hand. Had the two forces which acted upon the stone, viz. those of
projection and gravity, both produced uniform motion, the body must
certainly have descended through the diagonal; but since gravity, as
you have already learned, is an accelerating force, the body is made to
describe a curve instead of a straight line.
“This law, however, will require the aid of a diagram for its
explanation. Let X represent the ball at its greatest altitude, X Y the
force of gravity drawing it downward; and X Z that of projection. We
have here, then, two forces acting in the direction of the two sides of
a parallelogram. In passing on to Z, the ball will perform the diagonal
X _a_; and in the next equal space of time, will descend through
_three_ times the distance Z _a_, and will consequently be found at
_b_; while in the next period it will fall through _five_ equal spaces,
and pass to _c_; and in the next period, again, as it must fall _seven_
such spaces, it will reach the ground at _d_, having described a
portion of a curve from X to _d_, or during the time that the two
forces were in simultaneous operation. The same principle will explain
the curved ascent of the ball, substituting only the laws of retarded
for those of accelerated motion; for it is clear, that the body during
its _ascent_, will be retarded in the same degree in which it was
accelerated during its _descent_.”
[Illustration: Fig. 9. Diagram of a parabolic flight path.]
“Your explanation,” said Louisa, “appears very clear and satisfactory.”
“The curve which _Projectiles_ (that is to say, bodies projected into
the air) describe, is termed a _Parabola_ (16), although the resistance
of the air, which is not recognised in the theory, produces a
considerable influence on the practical result.”
The children now proceeded to amuse themselves with the sling. Louisa
challenged Tom to a trial of skill. She fancied that she could hurl a
stone with greater accuracy than her brother; but after several
contests she acknowledged herself vanquished, for Tom had succeeded in
striking the trunk of an old tree at a considerable distance, while his
sister was never able to throw the stone within several yards of the
mark.
“Well done, Tom!” exclaimed Mr. Seymour; “why you will soon equal in
skill the ancient natives of the Balearic Islands!”
“And were they famous for this art?” asked Louisa.
“With such dexterity,” replied her father, “did they use the sling,
that we are told their young children were not allowed any food by
their mothers, except that which they could fling down from the beam
where it was placed aloft. I fancy, however, Tom, that you would become
very hungry before you could strike an object in yonder poplar.”
“At all events, I will try,” said Tom.
He accordingly whirled round his sling, and discharged stone, which
flew forward with great velocity, but in a direction very wide from the
mark at which it was aimed. In the next moment a violent hallooing was
heard: it was from the vicar, who had narrowly escaped the boisterous
salutation of the falling stone, which, in its anxiety to throw itself
at the feet of the reverend gentleman, struck the beaver penthouse that
defended his upper story, and by a resolution of forces which we have
endeavoured to explain, darted off in the direction of the side of a
parallelogram, and was thus averted from the equally sensitive
antipodes of his venerable person, the brains in his head, and the
corns in his shoes.
“Upon my word, young gentleman!” cried the vicar, “I expected nothing
less than the fate of the giant of Gath.”
“My dear Mr. Twaddleton,” exclaimed Tom, in a tone of alarm, “I
sincerely hope that you have not been struck?”
“O no! thanks to my clerical helmet, I have escaped the danger which
threatened me: but, tell me, what new game is engaging your attention?”
Mr. Seymour said that he had been explaining the scientific principle
of the sling, and that he hoped the vicar was prepared to afford them
some information respecting its invention and history.
“The sling?” repeated the vicar; “why, bless me! I left you discoursing
upon elasticity; you really stride over province after province as
rapidly as if you were gifted with the seven-leagued boots of the
Ogre:--but to the point in question. The art of slinging, or casting
stones, is one of the highest antiquity, and was carried to a great
degree of perfection amongst the Asiatic nations. It was well known and
practised at a very early period in Europe; and our Saxon ancestors
appear to have been very expert in the use of this missile.”
Mr. Twaddleton, being desirous of communicating history of Major
Snapwell, begged that Mr. and Mrs. Seymour would allow him a few
minutes’ conversation; observing that the attention of the children
would be agreeably occupied during their absence by their
newly-acquired amusement.
“We will then, if you please, vicar,” replied Mr. Seymour, “walk to the
Geological Temple, where I have lately deposited some specimens which
you have not yet seen.”
“To speak sincerely,” said the vicar, “I cannot participate in that
high satisfaction which you appear to feel in collecting such hoards of
broken rocks and pebbles: where can lie the utility of such labour?
unless, indeed, in pursuance of your Utopian plans, you intend to
_Mac-adamise_ all the roads of science.”
“Is it nothing, my dear Mr. Twaddleton, to discover the structure of
different countries?”
“Which the geologist infers,” replied the vicar, “from a few
_patterns_, picked up at random on the road side!”
“Mr. Twaddleton,” said Mr. Seymour, “I will meet you on your own
ground: you are an antiquary; if an ancient monument of art be so
inestimable, is not a knowledge of the antiquity of the globe itself,
at least, of equal interest?”
“I understand you: you would infer that the scriptural account of the
Deluge is disproved by those Sciolists, who pretend to discover the
antiquity of the globe by penetrating its caverns, with as much ease as
the jockey ascertains the age of a horse by looking into its jaws.”
“You speak too flippantly of a class of philosophers who have united
their efforts to investigate a sublime subject upon the true principles
of science; were you to attend the meetings of the Geological Society,
and hear the discussions of its members, you would cease to talk thus
irreverently.”
“Although I may be unknown to your genii of the mountains, I am, at
all events, acquainted with a kindred class of philosophers who rival
them in industry, if not in talents; and notwithstanding the limited
range of their observations--being confined to the mountainous
districts they inhabit--I have little doubt but that their labours
have proved as acceptable to the world as those of the disciples of
Hutton or Werner. I once visited this district, and although the
language of its inhabitants was entirely unknown to me, I soon
discovered, by the aid of a glass, that they were in serious
discourse with each other; and one of the elders of the fraternity,
who was seated on a craggy precipice that overhung an extensive
valley covered with rich verdure, appeared, from his gestures, as if
pointing out to his fellow-labourers, who were digging in all
directions in search of treasure, the danger of an approaching
convulsion. While I was yet gazing, the fatal catastrophe actually
occurred; immense masses of the tottering strata rolled with
precipitous haste into the valley, involving in its ruin hundreds of
its inhabitants. It was extraordinary to behold the effects of this
shock upon those who were beyond the reach of its more destructive
influence; hundreds were seen scaling heights that appeared
inaccessible; others, stumbling--falling down frightful
precipices--rising again--helping, or pushing each other on--the
foremost serving as so many stepping-stones to those behind, who, in
their turn, hauled up the clusters over whose backs they had so
unceremoniously vaulted.”
“How awful!” cried Mrs. Seymour; “I never heard of any modern
catastrophe of such fearful extent: where did it occur?”
“The vicar doubtless alludes to the terrible earthquake of Messina, or
perhaps to that of Lisbon.”
“I neither allude to the one nor to the other,” cried Mr. Twaddleton;
“and yet, in some respects, the catastrophe which I have described
resembled that of Lisbon; for during the dreadful disaster human beings
seen to take advantage of the confusion to murder many of the
inhabitants, and to pillage their territories.”(17)
“For goodness’ sake!” cried Mrs. Seymour, “tell us at once where this
terrible event occurred.”
“In a fine Cheshire cheese!” exclaimed the vicar, “which had furnished
abundant food to the miniature republic of mites that occupied its deep
ravines and alpine heights. I think now,” continued the reverend
gentleman, “I am amply revenged for the allegorical jokes in which Mr.
Seymour has so often indulged at my expense.”
“I am well satisfied,” said Mr. Seymour; “for by repeating your
allegory to my children, I shall be enabled to convey a striking lesson
of wisdom. They will learn from it that there is not any pursuit,
however exalted, that may not be assailed by the weapons of ridicule,
especially when wielded by those penurious philosophers whose ideas of
utility are circumscribed within the narrow limits of direct and
immediate profit.”
“It is too true,” cried Mrs. Seymour, “that we are all apt to
depreciate those branches of knowledge which do not bear directly upon
the comforts or necessities of life; and the applications of geology
are, perhaps, so remote as scarcely to be discovered by the mass of
mankind.”
“There I must differ with you,” replied her husband: “to say nothing of
the practical advantages which have accrued to the miner from this
study, it has been the means of bringing hundreds of acres into
cultivation in districts where never a blade of grass had before
grown;(18) and if scholastic researches have thrown additional light on
scriptural subjects, they are no more to be compared with those of the
geologist on these occasions, than is the light of the glow-worm to
that of the sun.”
“Hey-day! what do I hear?” exclaimed the vicar. “Would you compare the
testimony of the Apamean medal with that of an unshapen flint?”
“I would rest my faith upon a _rock_,” replied Mr. Seymour; “the caves
of Buckland(19) have done more towards supporting the Mosaic account of
the Deluge than all the medals of the virtuoso. Fossils, in truth, are
to the geologist what medals are to the antiquary, preserving a record
of events which must otherwise have perished in the stream of time.”
Mr. and Mrs. Seymour and the vicar by this time arrived at the
Wernerian Temple, where, having discussed several points connected with
its objects, Mr. Twaddleton gave an account of Major Snapwell, whose
history created considerable interest, and determined Mr. Seymour to
call at Ivy Cottage, and invite its inmate to the Lodge.
[Illustration: Rock teetering on a ledge.]
-----
Footnote 16:
Footnote 16: A common plate will answer the purpose; but the black
surface gives the advantage of exhibiting more perfectly the motion
of the water during the progress of the experiment.
Footnote 17:
See page 54.
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[Illustration: Two boys rolling hoops along the ground using sticks.]