SCIENCE AND MAN. 339 



Perpetual motion was discarded before it was proved to 

 be opposed to natural law ; and, as regards the connec- 

 tion 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 

 bearing upon this question, which were published by 

 an anonymous writer in 1820. Roget'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 amounting to conviction, in 

 common, I believe, with other lovers of natural know- 

 ledge, 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 mutually 

 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 * magnetisation of light,' 

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

 Justice Grove made his mark upon this question. Cold- 

 ing, though starting from a metaphysical basis, grasped 

 eventually 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 in his dealings with scientific history 

 keeps his soul unwarped by envy, hatred, or malice, 

 personal or national, every fresh accession to historic 

 knowledge must be welcome. For every new-comer of 

 proved merit, more especially if that merit should have 

 been previously overlooked, he makes ready room in his 

 recognition or his reverence. But no retrospect of 



