230 INDUCTION. 



air not 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 di- 

 rection 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 simple laws, but had never tried the Torricel- 

 lian experiment, we might deduce its result from those laws. The known 

 weight of the air, combined with the position of the apparatus, would 

 bring tlie mercury within the first of the three inductions ; the first induc- 

 tion would bring it within the second, and the second within the third, in 

 the manner which we characterized 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; 

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

 perience would still be desirable, and might possibly be indispensable. 



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

 and have, therefore, been virtually affirmed in aflEirming 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 in science, wherever 

 regularity of any kind can be traced, to call the general proposition which 

 expresses the nature of that regularity, a law ; as when, in matbematics, 

 we speak of the law of decrease of the successive terms of a converging 

 series. But the expression laio of nature has generally been employed 

 with a sort of tacit reference to the oi'iginal sense of the word law, namely, 

 the expression of the will of a superior. When, therefore, it appeared that 

 any of the uniformities which were observed in natui'e, would result spon- 

 taneously from certain other uniformities, no separate act of creative will 

 being supposed necessary for the production of the derivative uniformities, 

 these have not usually been spoken of as laws of nature. According to 

 one mode of expression, the question, What are the laws of nature? may 

 be stated thus : What are the fewest and simplest assumptions, which be- 

 ing granted, the whole existing order of nature would result? Another 

 mode of stating it would be thus : What are the fewest general proposi- 

 tions from which all the uniformities which exist in the universe might be 

 deductively inferred ? 



Every great advance which marks an epoch in the progress of science, 

 has consisted in a step made toward the solution of this problem. Even a 

 simple colligation of inductions already made, without any fresh extension 

 of the inductive inference, is already an advance 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 suppositions which, instead of a much 

 greater number, would suffice to construct the whole scheme of the heav- 

 enly motions, so far as it was known up to that time. 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 to- 

 ward one another with a certain force, and have had a certain instantaneous 

 impulse originally impressed upon them. After this great discovery, Kep- 

 ler's three propositions, though still called laws, would hardly, by any per- 

 son accustomed to use language with precision, be termed laws of nature : 

 that phrase would be reserved for the simpler and more general laws into 

 w^hich Newton is said to have resolved them. 



