Our illustrations, this week, have reference to the center of gravity of bodies, or that point in any body about which all its weight may be said to be collected. Among the novelties which scientific investigation has added to our toys are several figures which will raise themselves upright when thrown down, and regain the erect position, notwithstanding their equilibrium is disturbed. The figures themselves are made of the pith of elder trees, or any other very light substance. Each is placed on half a bullet, as at A, or may be made to stand on its head as at B, by making its cap of lead. Their appearance is very droll when they are moved about, as they seem every moment to be falling over and yet continually right themselves. The philosophy of this is that the center of gravity being in the base and always trying to assume the lowest position, it keeps the figures upright. However much the equilibrium is disturbed, it will always try to regain its original position. This engraving represents what seems to te an astounding statement, namely, that a quarter or other piece of money can be made to spin on the point of a needle. To perform this experiment, procure a bottle, cork it, and in the cork place a needle. Now take another cork and cut a slit in it so that the edge of the coin will fit into the slit; next place two forks in the cork, as seen in the engraving, and placing the edge of the coin on the needle, it will spin round without falling off. The reason is this, that the weight of the forks, projecting as they do so much below the coin, brings the center of gravity of the arrangement much below the point of suspension or the point of the needle, and therefore the coin remains perfectly safe and upright.
This article was originally published with the title "Science in Sport" in Scientific American 13, 18, 144 (January 1858)