356 FRAGMENTS OF SCIENCE 



Scientific theories sometimes float like rumors in the 

 air before they receive complete expression. The doom 

 of a doctrine is often practically sealed, and the truth of 

 one is often practically accepted, long prior to the demon- 

 stration of either the error or the truth. Perpetual motion 

 was discarded before it was proved to be opposed to natu- 

 ral law; and, as regards the connection and interaction of 

 natural forces, intimations of modern discoveries are strewn 

 through the writings of Leibnitz, Boyle, Hooke, Locke and 

 others. 



Confining ourselves to recent times, Dr. Ingleby has 

 pointed out to me some singularly sagacious remarks bear- 

 ing upon this question, which were published by an anony- 

 mous writer in 1820. Eoget's penetration was conspicuous 

 in 1829. Mohr had grasped in 1837 some deep-lying truth. 

 The writings of Faraday furnish frequent illustrations of 

 his profound belief in the unity of nature. "I have 

 long," he writes in 1845, "held an opinion almost amount- 

 ing to conviction, in common, I believe, with other lovers 

 of natural knowledge, that the various forms under which 

 the forces of matter are made manifest have one common 

 origin, or, in other words, are so directly related and mu- 

 tually dependent, that they are convertible, as it were, one 

 into another, and possess equivalence of power in their 

 action." His own researches on magneto-electricity, on 

 electro-chemistry, and on the "magnetization of light," 

 led him directly to this belief. At an early date Mr. Jus- 

 tice Grove made his mark upon this question. Colding, 

 though starting from a metaphysical basis, grasped event- 

 ually the relation between heat and mechanical work, and 

 sought to determine it experimentally. And here let me 

 say that to him who has only the truth at heart, and who 



