142 THE POPULAR SCIENCE MONTHLY 



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, Bumford, Black, Miiller, 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 ex- 

 plain everything mechanically. Heat, for example, is a product of mo- 

 tion. 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, Rankin e, Clerk Maxwell, P. G. Tait and Balfour 

 Stewart. Working alone, Clausius, of Ziirich, 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 chem- 

 ical solutions by the use of the galvanic current. Without saying any- 

 thing 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 agen- 

 cies, 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. 



