SCIENCE AND MAN. 599 
Newton's transcendent mathematical genius raised it to 
the level of a demonstration. The whole of his deductions, 
moreover, rested upon the inductions of Kepler. Newton 
shot beyond his predecessors; but his thoughts were rooted 
in their thoughts, and a just distribution of merit would 
assign to them a fair portion of the honor of discovery. 
Scientific theories sometimes float like rumors iu 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 natural 
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 
anonymous writer in 1820. Roget's penetration was con- 
spicuous in 1829. Mohr had grasped in 1837 some deep- 
lying truth. The writings of Faiaday furnish frequent 
illustrations of his profound belief in the unity of nature. 
" 1 have long/' he writes in 1845, " held an opinion almost 
amounting 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 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-elec- 
tricity, on electro-chemistry, and on the "magnetization 
of light/' led him directly to this belief. At an early date 
Mr. Justice Grove made his mark upon this question. 
Colding, 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 newcomer of proved merit, more 
especially if that merit should have been previously over- 
