190 INDUCTION. 



pressing upon the surface of the mercury with the force which is called 

 its weight, or of the downward pressure on the mercury not being 

 propagated equally in an upward direction, or of a body pressed in 

 one direction and not in the direction opposite, either not moving in 

 the direction in which it is pressed, or stopping before it had attained 

 equilibrium. If we knew, therefore, the three simjile laws, but had 

 never tried the Torricellian experiment, we might deduce its result 

 from those laws. The known weight of the air, combined with the 

 position of the apparatus, would bring the mercury within the first of 

 the three inductions ; the first induction would bring it within the sec- 

 ond, and the second within the third, in the manner which we so fully 

 illustrated in treating of Ratiocination. We should thus come to know 

 the more complex uniformity, independently of specific experience, 

 through our knowledge of the simpler ones from which it results : al- 

 though, for reasons which will appear hereafter, verification by specific 

 experience would still be desirable, and might possibly be indis- 

 pensable. \ 



Complex uniformities which, like this, are mere cases of simpler 

 ones, and have, therefore, been virtually inferred in affimiing those, 

 may with propriety be called laws, but can scarcely, in the strictness 

 of scientific speech, be termed Laws of Nature. It is the custom of 

 philosophers, wherever they can trace regularity of any kind, to call 

 the general proposition which expresses the nature of that regularity, 

 a law ; as when, in mathematics, we speak of the law of decrease of 

 the successive terms of a converging series. But the expression, law 

 of nature, is generally employed by scientific men with a sort of tacit 

 reference to the original sense of the word latv, namely, the expression 

 of the will of a superior ; the superior, in this instance, being the Ruler 

 of the universe. When, therefore, it appeared that any o^ the uni- 

 formities which were observed in nature, would result spontaneously 

 from cei'tain other uniformities, without any separate act of creative 

 will, the former have not usually been spoken of as laws of nature. 

 According to another mode of expression, the question. What are the 

 laws of nature 1 may be stated thus : — What are the fewest and sim- 

 plest assumptions, which being granted, the whole existing order of 

 nature would result 1 Another mode of stating it would be thus : 

 What are the fewest general propositions from which all the uniformi- 

 ties which exist in the universe might be deductively inferred ? 



As has already been hinted (and will be more fully discussed here- 

 after) every gi'eat advance which marks an epoch in the progress of 

 science, has consisted in a step made towards the solution of this 

 problem. Even a simple colligation of inductions akeady made, with- 

 out any fresh extension of, the inductive inference, is already an ad- 

 vance in that direction. When Kepler expressed the regularity which 

 exists in the observed motions' of the heavenly bodies, by the three 

 general propositions called his laws, he, in so doing, pointed out 

 three simple volitions, by which, instead of a much greater number, it 

 appeared that the whole scheme of the heavenly motions, so far as yet 

 observed, might be conceived to have been produced. A similar, and 

 still greater step was made when these laws, which at first did not 

 seem to be included in any more general truths, were discovered to 

 be cases of the three laws of motion, as obtaining among bodies which 

 mutually tend towards one another with a certain force, and have had 



