4.—A PIN OR NEEDLE BALANCED HORIZONTALLY.
By another variation of the conditions it is possible to balance the pin upon the needle-point in a horizontal position and to make it revolve thereon in that situation. The only alteration necessary to the preparations already made is to substitute for the two forks two ordinary pocket-knives. By bending the handles of the knives at an angle to the blade, the pin may be sustained in a horizontal position. Or, by the substitution of a long needle for the pin, the forks may be retained as balance-weights, as in the previous example and as shown in the present illustration. The pin may be rested upon the needle-point as in the figure, and by a gentle touch of the finger may be set revolving. In time, by reason of the relative differences in hardness of the two metals, the commencement of a tiny hole will be drilled by the sharp steel point of the needle in the softer brass of the pin, and if the motion be continued for a sufficient length of time a hole will ultimately be an accomplished fact.
5.—THE SPINNING PLATE.
A further application of similar principles, and a plate may be balanced and spun upon the needle-point. The corked bottle with the needle in position remains as before. Two other corks are taken and split into two by a vertical cut. Into one end of each half-cork, upon the flat side, are stuck the prongs of a fork, and thus the four forks are hung at equal distances around the edge of the plate. Then, with a little care, the plate will be held in perfect equilibrium, as in Fig. 5.
6.—THE BALANCED EGG.
Next cut a slight concavity in one end of one of the corks, so as to adapt it as exactly as possible to one end of an egg. Then insert two forks, as before, into the sides of the cork, letting the hollowed-out end be the lower. Then rest the cork with the forks as counter-weights upon the end of the egg to which the concavity has been adapted. So aided, the egg may be balanced upon the mouth of the bottle, as in Fig. 6.