The invention of machines is the result of man's desire to save labor and to economize in the use of his own strength by utilizing, where possible, the natural forces of steam, wind, water, and electricity. Man possesses only a certain amount of energy. If one man works so fast as to exhaust himself by the end of the day, he will not accomplish so much in the long run as the workman who utilizes a little less than half his natural strength, and works at about one-third his greatest working speed.

Strength must be carefully distributed over the day's work, to obtain the best results. A machine never tires and can work almost constantly at its maximum practicable speed. It is for this reason that machines and labor-saving devices are continually being invented. These mechanical contrivances are the result of the experiences of the human race. The only tools that man possessed in the beginning were his hands and his teeth. As time went on he found that his hands and teeth were not sufficient, and he invented a club - a form of hammer. At later periods axes of stone, copper, bronze, and steel, and later the saw, plane, square, chisel, and file were invented. All these tools resulted from necessity, experience, observation, and the intelligent desire of the human race to save itself labor and toil.