forms it assumes. Having taken pains to conserve energy or to obtain it, the practical question is how to use it?
That energy is everywhere present, underlies all things, was affirmed by Young, Rumford, Black, Müller, Mohr, Liebig, J. B. Mayer, Joule, Carnot, Sir William Thomson, or Lord Kelvin. It was through their efforts chiefly that the theory gained acceptance. It began to attract notice during the first third of the century, although its acceptance even now is by no means universal. Faraday, Mohr and not a few others believed in the existence of something indestructible, connected with matter, yet independent of it, but Helmholtz and his school explain everything mechanically. Heat, for example, is a product of motion. Other natural processes explain other natural manifestations. This theory was brought forward and defended in great part by the Scotch school to which belong the illustrious names of the Thomsons, James and William, Rankine, Clerk Maxwell, P. G. Tait and Balfour Stewart. Working alone, Clausius, of Zürich, reached substantially the same results. Maxwell studied the energy of the electric magnetic field, Joule the energy of the electric current, Watt measured heat. The idea of the unity of all chemical combinations was suggested by Arrhenius, of Sweden, in 1886, who showed how to decompose chemical solutions by the use of the galvanic current. Without saying anything more of this physical theory which presupposes the universal existence of energy as a force in matter, if not a constituent of it, as something which can neither be created nor destroyed by human agencies, though it may, through its power of convertibility into various forms of power, be made extremely useful, we simply add that energy may be so accurately measured by the aid of mathematics that before it is called forth from its hiding place we can ascertain exactly what amount of work it will do. Merz says that this theory has been useful to science in at least four ways.
It has brought out clearer definitions of terms.
It has caused a revision and recasting of physical and chemical knowledge.
It has criticized existing theories from a new point of view.
From this new point of view fresh departures in the study of science have been taken.
What energy is we do not know. It appears as intensity and power to do work. Is it a substance, material in its nature? What need then of ether to carry the undulations which produce sound or vision? Whatever the answer to these enquiries and many others which might be raised, energy seems to be a regulative and a directive rather than a constructive principle. Energy is found everywhere, but it nowhere appears as creative, save in bringing particles of matter together in new forms, or passing itself from one form of existence to another without growing less in amount.