286 Prof. Challis on Newton's "Foundation of all Philosophy" 



existences as real as anything else is real, will be demonstrated 

 by such explanations, and with more and more evidence as the 

 number of the explanations is greater. This mode of philoso- 

 phizing was fully recognized in Newton's time, — the necessity 

 of appealing to observation and experience, both for the founda- 

 tions of philosophy and for the data requisite to make and verify 

 particular theoretical researches, being clearly understood. It 

 is particularly to be remarked that these two uses of experience 

 are broadly distinguished in Newton's writings. The latter is 

 met with continually; but the former is placed under the head 

 of Rules of Philosophizing, and is perhaps nowhere so distinctly 

 stated as in the third Rule. Newton there says, "hoc est fun- 

 damentum," using the singular number to indicate that the 

 principle of the method is the foundation of philosophy. 



Another objection may be made to these views on the ground 

 that if the pressure of the sether, and the relation of the pressure 

 to the density, be among the necessary foundations of theoretical 

 research, these facts must themselves remain unaccounted for. 

 To this I might reply that if the fundamental ideas of matter 

 and force suffice for the explanation of all phenomena and laws, 

 they will account for the pressure, and law of the pressure, of 

 air of given temperature, which are facts the same in kind as 

 those attributed to the aether. But it is unnecessary to adopt 

 this line of reasoning, which brings us to the verge of meta- 

 physics. It is sufficient to maintain that, if all phenomena and 

 laws can be shown by reasoning to be consequences of funda- 

 mental facts which are perfectly intelligible from sensation and 

 experience, the phenomena and laws are intelligibly accounted for. 



It is important further to remark that the fundamental ideas 

 above laid down respecting matter and force are by no means 

 arbitrary. I hold myself in no manner responsible for any of 

 them. The course of the argumentation by which they were 

 reached sufficiently shows, I think, that after the adoption of 

 the Newtonian principle of seeking for universal and fundamental 

 ideas from sensation and experience, no other than these could 

 be arrived at. All that I have done is to employ the same 

 principle in giving to the foundation of philosophy the larger 

 extent which is required by the existing state of experimental 

 physics. Not only, as I said above, are all phenomena explained 

 if the explanations are shown to rest on this foundation, but I 

 say further that there is absolutely no evidence that intelligible 

 explanations can rest on any other. Those who choose may 

 call the fundamental ideas hypotheses. They are, in fact, hypo- 

 theses in the proper sense of the Greek word, i. e. foundations. 

 But being in that respect necessary, they are quite distinct from 

 those which Newton referred to when he said " hypotheses non 



