NECESSARY TRUTHS— EFFECTS OF EXPERIENCE. 669 



stancj or ' conservation ' gives the name to the hypothesis 

 of molecules and central forces from which it was logically 

 deduced. 



Take any other mathematico-mechanical theory and it 

 is the same. They are all translations of sensible experi- 

 ences into other forms, substitutions of items between which 

 ideal relations of kind, number, form, equality, etc., obtain, 

 for items between which no such relations obtain ; coupled 

 with declarations that the exjjerienced form is false and the 

 ideal form true, declarations Avhicli are justified by the ap- 

 pearance of new sensible experiences at just those times 

 and places at which we logically infer that their ideal cor- 

 relates ought to be. Wave-hypotheses thus make us pre- 

 dict rings of darkness and color, distortions, dispersions, 

 changes of pitch in sonorous bodies moving from us, 

 etc. ; molecule-hypotheses lead to predictions of vapor- 

 density, freezing point, etc., — all which predictions fall true. 



Thus the world grows more orderly and rational to the 

 mind, which passes from one feature of it to another by de- 

 ductive necessity, as soon as it conceives it as made up of 

 so few and so simple phenomena as bodies with no proper^ 

 ties but number and movement to and fro. 



METAPHYSICAL AXIOMS. 



But alongside of these ideal relations between terms 

 which the world verifies, there are other ideal relations not 

 as yet so verified. I refer to those propositions (no longer 

 expressing mere results of comparison) which are formu- 

 lated in such metaphysical and aesthetic axioms as " The 

 Principle of things is one ;" " The quantity of existence is 

 unchanged ; " " Nature is simple and invariable ; " " Nature 

 acts by the shortest ways ; " " Ex nihilo nihil Jit ; " " Noth- 

 ing can be evolved which was not involved ; " "Whatever 

 is in the eflfect must be in the cause ;" "A thing can only 

 work where it is ; " "A thing can only affect another of its 

 own kind ; " " Cessante causa, cessat et effectus ; " " Nature 

 makes no leaps ; " " Things belong to discrete and perma- 

 nent kinds ; " " Nothing is or happens without a reason ; " 

 "The world is throughout rationally intelligible;" etc., 



