“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.