4 FKAGMENTS OF SCIENCE. 



ment on the part of those who held it. Gradually, how- 

 ever, as men became more and more acquainted with the 

 true functions of machinery, the dream dissolved. The 

 hope of getting work out of mere mechanical combina- 

 tions disappeared: but still there remained for the 

 speculator a cloud-land denser than that which filled 

 the imagination of the Tyrolese priest, and out of 

 which he still hoped to evolve perpetual motion. There 

 was the mystic store of chemic force, which nobody 

 understood; there were heat and light, electricity and 

 magnetism, all competent to produce mechanical 

 motion.* Here, then, was the mine in which our gem 

 must be sought. A modified and more refined form 

 of the ancient faith revived; and, for aught I know, 

 a remnant of sanguine designers may at the present 

 moment be engaged on the problem which like-minded 

 men in former ages left unsolved. 



And why should a perpetual motion, even under 

 modern conditions, be impossible? The answer to this 

 question is the statement of that great generalization 

 of modern science, which is known under the name of 

 the Conservation of Energy. This principle asserts 

 that no power can make its appearance in nature with- 

 out an equivalent expenditure of some other power; 

 that natural agents are so related to each other as to 

 be mutually convertible, but that no new agency is 

 created. Light runs into heat; heat into electricity; 

 electricity into magnetism; magnetism into mechanical 

 force; and mechanical force again into light and heat. 

 The Proteus changes, but he is ever the same; and 

 his changes in nature, supposing no miracle to super- 

 vene, are the expression, not of spontaneity, but of 

 physical necessity. A perpetual motion, then, is 

 deemed impossible, because it demands the creation of 



* See Helmholtz : ' Wechselwirkung der Naturkrafte.' 



