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 “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 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.” Two jokers connected by poles and strings descending some steps. 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. “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 “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 “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 Tom keeping the pith-ball aloft by blowing into the tube. 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. “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.” “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.” Man sitting at the top of a fountain’s stream of water. 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 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 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. 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 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; “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 “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, “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 “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 “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 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. 11.Upon this subject, Dr. Brewster’s Introductory Letter on Natural Magic will be read with interest and advantage. 12.The comparative inelasticity of water will be shown hereafter. 13.Pollux, lib. ix. c. 7. |