Page:Life in Motion.djvu/166

146 of energy represented by the fuel he uses, and he can estimate the amount of effective mechanical energy he can get out of it by the best arrangements yet devised. We are told that the best triple expansion steam-engine, with the best arrangement of furnaces and boilers, gives back of effective mechanical energy only about twelve and a half per cent of the total energy in the fuel. This means that of every one hundred parts of energy supplied to the engine only twelve and a half parts are of any use, the remaining eighty-seven and a half parts being lost as heat. The case is worse when we consider an ordinary locomotive, by which only about four per cent of the total energy becomes effective. It is interesting to inquire how the muscle, considered as a little engine, compares with the best steam-engine.

So long ago as 1869, Professor Fick of Wtirtzburg stated that the amount of energy transformed into mechanical energy by a muscle was about thirty-three per cent of the energy in the food stuffs. In 1878, he announced that more accurate experiments had obliged him to reduce the estimate to twenty-five per cent. Fick's experiments were made on the