_The Chinese Tumblers, illustrating the joint effects of change in
the centre of gravity of a body, and of momentum.--Mr.
Twaddleton’s arrival after a series of adventures.--The Dancing
Balls.--The Pea-shooter.--A figure that dances on a
fountain.--The Flying Witch.--Elasticity.--Springs.--The game of
“Ricochet,” or Duck and Drake.--The Rebounding Ball.--Animals
that leap by means of an elastic apparatus.--A new species of
puffing, by which the Vicar is made to change countenance._
Early on Monday morning did the young group assemble in the library;
they had been told by Mrs. Seymour that their father had received a new
toy of a very interesting and instructive nature, and we can easily
imagine the eagerness with which they anticipated the sight of it.
“I trust,” said Mr. Seymour, “that after our late discussion, the
subject of the centre of gravity is thoroughly understood by you all. I
have also reason to think that the nature and effects of what is termed
_momentum_ have been rendered intelligible to you.”
“I certainly understand both those subjects,” answered Tom; and so
thought the rest of the party.
“Well, then, I will put your knowledge to the test,” observed Mr.
Seymour, “for you shall explain to me the mechanism of these _Chinese
Tumblers_.” Upon which he produced an oblong box, which, by opening,
formed a series of stairs or steps, and took from a drawer at its end
two grotesque figures (_Clown_ and _Pantaloon_), which were connected
with each other by two poles, which they appeared in the attitude of
carrying, pretty much in the way that the porters carry the poles of a
sedan-chair. The foremost figure was then placed upon the top step,
when, to the great astonishment of the whole party, the figures very
deliberately descended the several stairs, each turning over the other
in succession.
“There was a period in our history,” observed Mrs. Seymour, “when so
marvellous an exhibition would have subjected the inventor to the
penalties of sorcery.”
“That,” remarked Mr. Seymour, “may be said of most of the other
inventions which I have yet in store to illustrate the powers conferred
upon us by a knowledge of natural philosophy; but, as far as mechanical
skill is concerned, I doubt whether the ancients did not even surpass
us, especially in the art of constructing automata; and as quicksilver
was known in the remotest ages, I think it not improbable that it was
one of the agents employed by them on such occasions. If I remember
right, Aristotle describes a wooden Venus, which moved by means of
‘_liquid silver_;’ then, again, the moving tripods which Apollonius saw
in the Indian temples--the walking statues at Antium, and in the temple
of Hierapolis, and the wooden pigeon of Archytas,[11] ought,
undoubtedly, to be regarded as evidences of their mechanical resources.
But let us reserve these literary questions for the better judgment of
our worthy friend the vicar, and proceed to consider the mechanism of
the toy before us. Tom,” continued he, “take the figures in your hand
and examine them.”
No sooner had the young philosopher received the figures from the hand
of his father than he declared that the tubes were hollow, and that he
felt some liquid running backwards and forwards in them.
“You are quite right, my boy,” said Mr. Seymour, “they contain
quicksilver.”
“Now then I understand it,” cried Tom; “the quicksilver runs down the
tubes and alters the centre of gravity of the figures, and so makes
them tumble over each other.”
“Well, I acknowledge that is no bad guess as a beginning, and will
certainly explain the first movement; but you will be pleased to
recollect that the instant a new centre of gravity is thus produced the
figures must remain at rest--how, then, will you explain their
continued motion?”
“You said something, I think, about momentum; did you not, papa?”
“Certainly; and to its agency the continuance of the motions is to be
ascribed: but I will explain the operation more fully.”
Mr. Seymour then proceeded to point out the mechanism and movements of
the toy in a manner which we shall endeavour to convey to our readers
by the aid of the annexed engraving.
[Illustration: Two jokers connected by poles and strings and in the
process of descending some steps.]
“As soon as the figure A is placed upon the step D, in the position A
B, the quicksilver, by running down the inclined tubes, swings the
figure B round to C; and the centre of gravity having been thus
adjusted, the whole would remain at rest but for the contrivance to be
next described. Besides their connexion with the poles by means of
pivots, the figures are connected with each other by silken strings,
which keep the figure B steadily in its position, while it traverses
the arc until it arrives at C, when their increased tension has the
effect of capsizing it, and of thus producing a momentum, which, by
carrying its centre of gravity beyond the line of direction, causes it
to descend upon the step E, when the quicksilver, by again flowing to
the lowest part of the tubes, places the figures in the same position,
only one step lower, as they were at the commencement of their action;
and thus, by successive repetitions of the same changes, it is quite
evident that the figures must continue to descend as long as any steps
remain for their reception.”
“I understand it perfectly,” observed Louisa, with a smile of
satisfaction.
“I need scarcely say,” continued Mr. Seymour, “that there are some
niceties in the adjustment of the minuter parts of the apparatus,
without which the effect could not be accomplished; the quantity of
quicksilver, for instance, must bear its proper proportion to the
weight and dimensions of the figure: and in order to prevent its too
rapid passage along the inclined tubes, strings are stretched across
their interior to retard the stream. Then, again, some management is
necessary with regard to the silken strings, in order to ensure a
necessary degree of tension. I will now show you,” said he, “a single
tumbler, which will perform the same motions without the assistance of
any tubes.”
“But not without quicksilver,” observed Tom, “which, I suppose, must,
in this case, be put into the body of the figure.”
“You are quite right; and it is made to pass from one extremity of its
body to the other through a small orifice, which has the same effect as
the strings in the tubes, in breaking the current and preventing its
too rapid motion. In all other respects, the principle is the same as
in the double figures.”
Just as Mr. Seymour had terminated his exhibition of ‘_Le petit
Culbuteur_,’ the welcome appearance of the vicar infused fresh spirits
into the little party.
“My dear friends,” said Mr. Twaddleton, “I have been most provokingly
detained by that tiresome etymologist Jeffrey Prybabel. I made many
efforts to escape, but I was as a fly in a cobweb.”
“He is the greatest bore in all Christendom; I knew him well,” observed
Mr. Seymour, “when he practised as a Conveyancer in Gray’s-Inn, and
went by the nickname of the Riot Act; for, in such horror was he held,
that, if a number of persons were congregated, his approach was sure to
disperse them. But what has been the subject of your discourse?--was
the etymologist merely airing his vocabulary, or did he propose some
difficult question for discussion? Be this, however, as it may, I will
venture to say that he was, as usual, loquacious on the subject of
_mutes_--dry on the use of _liquids_, and descanting without end on the
importance of a _termination_?”
“Mr. Seymour, I am really and truly ashamed of you; punning, under any
circumstances, is a most disgraceful habit, but when employed to
distort the meaning of language it becomes absolutely criminal.”
To turn the subject of this discourse, the vicar proceeded to inform
Mr. Seymour that he had no sooner escaped from the fangs of Prybabel
than he encountered _Polyphemus_. Our readers may, perhaps, wonder who
this _Polyphemus_ could have been; we must, therefore, inform them that
Mr. Twaddleton, whose ideas were always tinctured with classical
colouring, had bestowed this appellation upon the renowned Dr. Doseall,
the Esculapius of Overton, because, as he said, his practice was like
the Cyclops, _strong but blind_; and Mr. Seymour declared that the
similitude was even more perfect than the vicar had contemplated, for
he observed that he certainly fattened upon the unhappy victims who
fell within his clutches.
With all our respect for the liberality of Mr. Seymour and the
kind-heartedness of the vicar, we must, in justice to this respectable
son of Apollo, express our disapprobation at so unprovoked a sarcasm.
We acknowledge that Dr. Doseall, by the aid of low bows and high
charges--of little ailments and large potions, had contrived to secure
a very comfortable balance on the creditor side of his worldly ledger.
We also admit, that after the example of other celebrated physicians,
he had one sovereign remedy, which he administered in every disease.
But what of that? he was often successful in his cures--that is to say,
his patients sometimes recovered _after_ they had taken his physic; and
is not that the test conventionally received in proof of the skill or
ignorance of greater physicians than Dr. Doseall? Nor can we persuade
ourselves into the belief, that a doctor who faithfully adheres to one
single remedy, is less likely to be right than those restless spirits
who are eternally coquetting with all the preparations of the
Pharmacopœia without ever remaining steady to any one of them. It has
been truly remarked, that the clock which stands still and points
steadfastly in one direction, is certain of being right twice in the
twenty-four hours, while others may keep going continually, and as
continually going wrong. Being ourselves no doctors, we merely throw
out this hint for the consideration of those who are learned in such
matters: but we beg pardon of our readers for this digression.
“Well,” said Mr. Seymour, “I am, at all events, rejoiced to see our
Trojan in safety, after such perilous adventures; and I hope that he is
now prepared to set sail again with us, on a new voyage of discovery. I
have been engaged,” continued he, “in explaining still farther the
nature of momentum, and I now propose to exhibit an experiment of a
different kind, in order to illustrate the same subject. You, no doubt,
remember,” continued Mr. Seymour, “that velocity makes up for weight:
although, therefore, a fluid, as air, or water, may, in a state of
quiescence, be unable to support a body, yet, by giving it a certain
velocity, it may acquire a sustaining power. I have here several gilded
pith-balls, through one of which I have run two pins, at right angles
to each other: the naked points, you perceive, are defended with
sealing-wax, to prevent any mischief that might arise from their
accidentally coming into contact with your face. By means of this brass
tube, (the stem of a tobacco-pipe will answer the same purpose,) I
shall produce a current of air by my breath, and you will observe that
the little ball will continue to dance, as if unsupported.”
Mr. Seymour then placed the pith-ball at the end of the pipe, and,
inserting its other extremity in his mouth, blew out the ball, which
immediately rose in the air, and continued to float about for several
seconds: he then drew in his breath, and caught it with much address on
one of its points; and in this manner, alternately floating and
catching it, did he continue to delight the wondering group for several
minutes.
Tom received the tube and ball from the hand of his father, and soon
succeeded in playing with it. Observe, gentle reader, the address with
which the boy manages it.
[Illustration: Tom keeping the pith-ball aloft by blowing into the
tube.]
“This reminds me of my pea-shooter,” said Tom, as he removed the tube
from his mouth, “with which I have often shot a pea across the
play-ground.”
“Exactly; and you will now understand the nature of the force by which
your pea was projected. The air blown from the lungs, gains such
momentum from the contracted channel in which it flows, as to impart
considerable velocity to the pea placed within the influence of its
current.”
Mrs. Seymour observed, that she had lately read in Waterton’s
“Wanderings in South America,” a very interesting account of the Indian
blow-pipe, which the natives of Guiana employ as an engine for
projecting their poisoned arrows, and which owes its power to the
principle of which Mr. Seymour had just spoken, and its unerring
accuracy to the skilful address of the Indian who uses it.(10)
“Mr. Seymour,” said the vicar, “I much like your experiment with the
pith-balls; but do tell me the use of the pins that are passed through
them.”
“They are not absolutely necessary for the success of the experiment:
indeed, I ought to have stated, that their only use is to ensure the
elevation of the ball to a certain distance above the orifice of the
tube, before it is set adrift.”
“‘_Ne turbata volent rapidis ludibria ventis_,’ as Virgil has it. I
duly appreciate the contrivance; but if the ball was set off at a
distance from the orifice, such an expedient would be unnecessary.”
“Certainly,” answered Mr. Seymour; “I will soon convince you that,
under the condition you propose, the pins are not essential.”
So saying, he placed the tube in his mouth, and by carefully holding
the ball at a distance of about half an inch from its orifice, he was
enabled to consign it at once to a continuous and steady stream of air,
which can never be commanded at the point from which the air issues;
and he thus succeeded in sustaining the ball in motion, in the same
manner as he did in the preceding experiment.
“We will now proceed to the orchard,” said Mr. Seymour, “where I have
prepared another pleasing exhibition of a similar description.”
The party accordingly left the Lodge, and when they had arrived at the
fountain, their father produced a small wooden figure, of which the
annexed is a sketch. Within its base was fixed a hollow sphere, or ball
of thin copper, which, when properly adjusted on a fountain, or _jet
d’eau_, was sustained by the momentum produced by the velocity of the
stream; so that the whole figure was balanced, and made to dance on the
fountain, as the pith-ball had been made to play in the current of air.
[Illustration: Man sitting at the top of a fountain’s stream of water.]
The children were much gratified at witnessing so curious an
exhibition. Mr. Twaddleton laughed heartily at the ludicrous effect it
produced, and observed that, although he had never before seen the
experiment, he had frequently heard of it; and he added, that he
understood it to be a very common toy in Germany and Holland.
“I have for some time,” said Mrs. Seymour, “been trying to construct a
light figure of this kind, which shall dance on a current of air; and I
believe I have at length succeeded. The head I have formed of the seed
vessel of the _Antirrhinum_, which has a striking resemblance to a
face, and possesses, moreover, the indispensable condition of
lightness. The dress is made of silver paper, stretched over a cone of
the same material. From its appearance I have named it the _Flying
Witch_.”
“I admire your ingenuity,” said Mr. Seymour, “and I have no reason to
doubt the success of your enterprise.”
“I found it convenient,” continued Mrs. Seymour, “to place a stage of
card below the orifice of the tube, in order to steady the figure as
she rises, and to receive her as she falls.”
“Your principal care,” observed her husband, “must be to throw the
centre of gravity of the figure as low as possible.”
On the party returning to the library, Mr. Seymour expressed a wish
that, before they suspended their morning’s recreations, they should
take into consideration a peculiar property of matter, which they had
not yet discussed.
“And what may that be?” asked Louisa.
“ELASTICITY,” replied her father; “and I wish to hear whether Tom can
explain to us the meaning of the term.”
Tom very well knew what was meant by Elasticity; but he was like many a
merchant with a bill of exchange, who, although well acquainted with
its value, has not sufficient small change to cash it. Tom wanted words
to enable him to furnish a clear definition; his father, therefore,
kindly relieved his embarrassment, by informing him that “it was a
property inherent in certain bodies, by which they possessed a
disposition to have their form altered by force or pressure, and to
recover it on the removal of that pressure, throwing off the striking
body with some degree of force: for example,” continued he, “the cane
which I hold in my hand can be bent to a certain extent, and then, if I
let it go, it will immediately return to its former condition with
considerable force.”
Louisa inquired whether bending and pressing upon a body were the same
thing. Mr. Seymour replied, that the form of an elastic body might be
altered either by compression or distension, and that _bending_ was, in
fact, only a combination of these two methods; “For,” said he, “when a
straight body, like my cane, is bent, those particles of it which are
on the one side are compressed, while those on the other are distended.
But let us proceed with the subject. I have said that elastic bodies,
on returning to their original form, throw off the striking body with
some degree of force. I have here,” continued Mr. Seymour, taking out
of his pocket a wooden image of a cat, “a toy which I intend as a gift
to John; it will serve to illustrate our subject. The tail, you
perceive is movable, one of its ends being tied to a piece of catgut,
which is a highly elastic substance. When I bend the tail under the
body of the animal, I necessarily twist the string; and by pressing the
other end of the wooden tail upon a piece of wax, I can retain it for a
few seconds in that situation.”
Mr. Seymour having fixed the tail in the manner above described, placed
the wooden image on the ground, when, in a few seconds, it suddenly
sprang forward, to the great delight of the younger children.
“Can you explain this action?” asked Mr. Seymour.
“The wax,” answered Tom, “was incapable of holding the end of the tail
longer than a few seconds; and as soon as it was let loose, the
elasticity of the catgut enabled it to return to its former condition;
in doing which the tail struck with force against the ground, which
threw off the body of the cat and produced the leap.”
“Very well explained; and you, no doubt, will readily perceive that the
operation of steel springs depends upon the same principle of
elasticity: a piece of wire or steel, coiled up, may be made to set a
machine in motion by the endeavour it makes to unbend itself. This is
the principle of the spring in a watch. When our watches are what is
termed _down_, this steel has uncoiled itself; and the operation of
winding them up, is nothing more than that of bending it again for
action.(11) If the elasticity of a body be _perfect_,” added Mr.
Seymour, “it will restore itself with a force equal to that with which
it was compressed. As I have given John a toy, it is but fair that I
should reward you, Tom: open that box, and examine the gift which it
contains.”
Tom received the present from his father, and proceeded to open the
lid, when, to his great astonishment, the figure of an old witch
suddenly sprang upwards. Mr. Seymour explained its mechanism, by
stating “that the figure contained a wire coiled up like a corkscrew,
and which, upon the removal of the pressure of the lid which confined
it, immediately regained its original form.”(12)
Tom inquired what kind of bodies was most elastic. He was informed that
the air was the most elastic of all known substances, and had, for that
reason, been distinguished by the name of an _elastic_ fluid. Hard
bodies were so in the next degree; while soft substances which easily
retain impressions, such as clay, wax, &c. might be considered as
possessing but little elasticity.
“I should have thought,” said Louisa, “that neither clay nor wax had
possessed _any_ elasticity.”
“My love, we know not any bodies that are absolutely, or perfectly,
either hard, soft, or elastic; since all partake of these properties,
more or less, in some intermediate degree. Liquids are certainly the
least elastic of all bodies; and, until lately, water was regarded as
being perfectly inelastic;[12] but recent experiments have shown it
capable of compression, and of restoring itself to its original bulk,
as soon as the pressure is removed; it must, therefore, possess some
elasticity. Indeed,” said Mr. Seymour, “we might have anticipated such
a result from the effects which present themselves in the well-known
game of ‘_Ricochet_,’ or _Duck and Drake_.”
“_Duck and Drake!_” exclaimed Louisa; “for goodness’ sake, what can
that game be?”
“I dare say your brother will not have any difficulty in explaining it
to you.”
Tom informed her that it was a game in which any number of boys threw a
stone, or a flat piece of tile, into the water; and that he whose stone
rebounded the greatest number of times was the conqueror.
“It is a very ancient game,” said Mr. Seymour, “and had the vicar been
present, we should have heard a learned disquisition upon it; as he,
however, is unfortunately absent, I must tell you all I know upon the
subject. It was called by the Greeks _Epostrakismos_,[13] and was
anciently played with flat shells. Now it is evident that the water
must possess some degree of elasticity, or the stone could not
rebound(13); but I shall have occasion to revert to the subject
hereafter.”
“And are my marbles elastic?” asked Tom.
“Undoubtedly; but not to the same extent as your ball. There,” said Mr.
Seymour, throwing his ball against the wall, “see how it rebounds.”
“The return of the ball,” observed Tom, “was, I suppose, owing to its
elasticity; and I now understand why one filled with air rebounds so
much better than one stuffed with bran or wool.”
“You are quite right; and the return of the ball, after having struck
the wall, affords an example of what is termed _reflected_ motion, upon
which I shall have to remark when we come to the interesting subject of
‘Compound Forces;’ but at present, my only wish is to render the
property of elasticity intelligible to you. It is a force of very
extensive application; there is scarcely a machine wherein the
elasticity of one or more solids is not essentially concerned. Nature,
also, avails herself of this property to accomplish many of her
purposes. Fleas and locusts are enabled to jump two hundred times the
height of their own bodies by means of a springy membrane, easily
visible by a microscope; so that, supposing the same relative force to
be infused into the body of a man six feet high, he would be enabled to
leap three times the height of St. Paul’s: and the regular dispersion
and sowing of the seeds of several plants is effected by a spring,
which is wound sometimes round the outside, and at others, round the
inside, of the case in which the seeds are contained.”(14)
“I suppose,” said Tom, “that it is by some such spring shrimps are
enabled to leap to the tops of cataracts, as I have read in my work on
Natural History.”
“Many species of fish are thus enabled to leap, by bending their bodies
strongly, and then suddenly unbending them with an elastic spring; and
the long-tailed crayfish, and the common shrimp, leap by extending
their tails, after they have been bent under their bodies:--but the
most striking example of this kind is the leap of the salmon; just
under the cataract, and against the stream, he will rush for some
yards, and rise out of the spray six or eight feet; and, amidst the
noise of the water, he may be heard striking against the rock with a
sound like the clapping of hands; if he find a temporary lodgment on
the shelving rock, he will lie quivering and preparing for another
summerset, until he reaches the top of the cataract; thus at once
exhibiting the elasticity of his bones and the power of his muscles.”
“We will now conclude our diversions,” said Mr. Seymour, “with an
exhibition of a very striking description. Here,” cried he, as he
removed a small piece of apparatus from a box which stood on the table,
“is a toy, at which the sternest philosopher, nay, even Heraclitus, of
weeping memory, could not refrain from laughing.”
He then displayed a small ball of Indian rubber, on which was painted
an exact resemblance of the worthy vicar, executed under the direction
of Mr. Seymour, by that inimitable artist, George Cruikshank. The ball
was connected with an air syringe, by which it was easily distended. It
gradually increased in magnitude, swelling, like the gourd of Jonah, as
the inflation proceeded, and the countenance of the vicar progressively
enlarged to the size of the full moon, without the least alteration in
the character or expression of its features.
“I declare,” said Mr. Seymour, “the vicar _improves upon acquaintance_.”
“It must be acknowledged that you have _puffed_ him into consequence,”
observed Mrs. Seymour.
The countenance had, after a short time, swelled to ten times its
original dimensions: the children deafened Mr. Seymour with their
shouts, and the good-humoured clergyman was actually convulsed with
laughter. The stop-cock was now turned; the elastic bladder became
smaller and smaller, and the features underwent a corresponding
diminution, until they once again assumed their original dimensions.
“You perceive, my dear Sir, that I make you _look small_ again.”
“That is by no means an unusual effect of your jokes,” replied the
vicar.
“Now, Tom,” said his father, “it is for you to explain the nature of
the exhibition you have just witnessed.”
Tom proceeded accordingly.
“The bladder was highly elastic, and therefore readily yielded to the
pressure of the air, and became distended. As soon, however, as the
pressure was removed, the air was driven out again with force, and the
particles of the Indian rubber returned to their former condition. But
I observed one circumstance which I do not understand,” said Tom: “when
you first turned the stop-cock, the air rushed out with great violence,
and the ball diminished very rapidly; but it gradually slackened,
until, at last, the bladder could scarcely be seen to contract.”
“I rejoice to find that you were so observant,” said his father: “the
effect you noticed depended upon a general law of elasticity. Elastic
bodies, in the recovery of their forms from a state of compression,
after the removal of the compressing force, exert a greater power at
first than at last, so that the whole progress of restoration is a
_retarded_ motion.”
The vicar, who had listened with profound attention to the explanation
which the boy had offered, rushed forward at its conclusion, and
clasping him in his arms, declared, that a first-class man of Trinity
could not have succeeded better.
“But let us now, if you please, Mr. Seymour, suspend our researches:
recollect,” said the vicar, “that your birds are, as yet, scarcely
fledged; and they will, therefore, make greater advances by short
flights frequently repeated, than by uninterrupted progression.”
We heartily concur in this opinion, and shall, therefore, terminate the
chapter.
-----
Footnote 11:
Upon this subject, Dr. Brewster’s Introductory Letter on Natural
Magic will be read with interest and advantage.
Footnote 12:
The comparative inelasticity of water will be shown hereafter.
Footnote 13:
Pollux, lib. ix. c. 7.
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