338 INDUCTION. 



The laws, thus explained oi* resolved, are sometimes said to be accounted 

 for; but the expression is incorrect, if taken to mean any thing more than 

 what has been already stated. In minds not habituated to accurate think- 

 ing, there is often a confused notion that the general laws are the causes of 

 the partial ones ; that the law of general gravitation, for example, causes 

 the phenomenon of the fall of bodies to the earth. But to assert this 

 would be a misuse of the word cause : terrestrial gravity is not an effect of 

 general gravitation, but a case of it; that is, one kind of the particular in- 

 stances in which that general law obtains. To account for a law of nature 

 means, and can mean, nothing more than to assign other laws more general, 

 together with collocations, which laws and collocations being supposed, the 

 partial law follows without any additional supposition. 



CHAPTER XIIT. 



MISCELLANEOUS EXAMPLES OF THE EXPLANATION OF LAWS OF NATURE. 



§ 1. The most striking example which the history of science presents, 

 of the explanation of laws of causation and other uniformities of sequence 

 among special phenomena, by resolving them into laws of greater simplic- 

 ity and generality, is the great Newtonian generalization ; respecting 

 which typical instance, so much having already been said, it is sufficient to 

 call attention to the great number and variety of the special observed uni- 

 formities, which are in this case accounted for, either as particular cases, or 

 as consequences, of one very simple law of universal nature. The simple 

 fact of a tendency of every particle of matter toward every other particle, 

 varying inversely as the square of the distance, explains the fall of bodies 

 to the earth, the revolutions of the planets and satellites, the motions (so 

 far as known) of comets, and all the various regularities which have been 

 observed in these special phenomena; such as the elliptical orbits, and the 

 variations from exact ellipses ; the relation between the solar distances of 

 the planets and the duration of their revolutions ; the precession of the 

 equinoxes ; the tides, and a vast number of minor astronomical truths. 



Mention has also been made in the preceding chapter of the explanation 

 of the phenomena of magnetism from laws of electricity ; the special laws 

 of magnetic agency having been affiliated by deduction to observed laws 

 of electric action, in which they have ever since been considered to be in- 

 cluded as special cases. An example not so complete in itself, but even 

 more fertile in consequences, having been the starting-point of the really 

 scientific study of physiology, is the affiliation, commenced by Bichat, and 

 carried on by subsequent biologists, of the properties of the bodily organs, 

 to the elementary properties of the tissues into which they are anatomical- 

 ly decomposed. 



Another striking instance is afforded by Dalton's generalization, com- 

 monly known as the atomic theory. It had been known from the very 

 commencement of accurate chemical observation, that any two bodies com- 

 bine chemically with one another in only a certain number of proportions ; 

 but those proportions were in each case expressed by a percentage — so 

 many parts (by weight) of each ingredient, in 100 of the compound (say 

 35 and a fraction of one element, 64 and a fraction of the other) ; in which 

 mode of statement no relation was perceived between the proportion in 



