Over the mouth of it you are to stretch and lap with a piece of waxed string a thin film of sheet india-rubber. You want to get some liquid, water in our present case, into this apparatus. Well, dip the fine-drawn hollow spill into a vessel containing water, press the india-rubber drumhead with finger-tip, and air bubbles will come out. Remove the pressure, and water flows in. Removing now the immersed spill, water to any graduated amount can be injected into the walnut by pressure on the drumhead—and, what is more, taken out again if necessary. All this could be done by a syringe, but not so neatly or conveniently.
By exercising the necessary amount of care in adjustment, it would be quite possible to dispense with the leaden-weight attachment to your little man altogether. This is sometimes done, and when done the toy is all the prettier.
Of course, no long explanations are needed to explain the mode of action of the toy. Pressure on the drumhead transfers itself to the air volume inside the bottle; the compressed air in its turn presses upon the water. Now water, unlike air, is inelastic—it cannot be made to occupy smaller space by any force you could apply; so up goes a portion of water temporarily into the walnut-shell, only to come out again on removal of the pressure.
CHAPTER LXIII.—MECHANICAL AND OTHER PUZZLES.
I.—Some Mechanical Puzzles.—By F. Chasemore.
(1) The Balance Puzzle.—Cut a piece of cardboard four inches square. In the middle punch two holes, and punch a hole also in each corner. Take four pieces of thread eight inches long and knot the ends together; then pass one thread through each corner hole of the card and fasten them there by tying a bead to each. Now take another piece of thread eighteen inches long and double it in the middle, then pass the loop down through one of the holes in the middle of the card and up through the other hole, and pass the loop through a small ring. Next pass the ends of the thread through the loop and draw it tight, and fasten the ends to the knot joining the four other threads ([Fig. 1]). The puzzle is to get the ring off the threads without cutting them.