THE SCIENTIFIC LAW 83 



entire product of " things-in-themselves," are probably but 

 the smallest portion of their " capacity for producing " 

 sense-impression. Hence to talk about natural law as 

 existing in " things-in-themselves " and apart from man's 

 mind is again to assert an unmeaning x among an un- 

 thinkable y and z (p. 75). If nature for man is con- 

 ditioned by his perceptive and retentive faculties, then 

 natural law is conditioned by them also. It has no 

 relation to something above and beyond man, but solely 

 to the special products of his perceptive faculty. We 

 have no right to infer its existence for things without a 

 perceptive faculty, or even for perceptive faculties not 

 closely akin to man's. I believe that a great deal of the 

 obscurity involved in popular ideas about " Nature " would 

 have been avoided had this been borne in mind. 



A good instance of the relativity of natural law is to 

 be found in the so-called Secotid Law of Thermo-dynaniics. 

 This law resumes a wide range of human experience, that 

 is, of sequences observed in our sense-impressions, and 

 embraces a great number of conclusions not only bearing 

 on practical life, but upon that dissipation of energy which 

 is even supposed to foreshadow the end of all life. The 

 appreciation of the relativity of natural law is so important 

 that the reader will, I trust, pardon me for citing the 

 entire passage in which Clerk -Maxwell discusses this 

 instance : — ^ 



" One of the best-established facts in thermo-dynamics 

 is that it is impossible in a system enclosed in an envelope 

 which permits neither change of volume nor passage of 

 heat, and in which both the temperature and pressure 

 are everywhere the same, to produce any inequality of 

 temperature or of pressure without the expenditure of 

 work. This is the second law of thermo-dynamics, and 

 it is undoubtedly true so long as we can deal with bodies 

 only in mass, and have no power of perceiving or handling 

 the separate molecules of which they are made up. But 

 if we conceive a being whose faculties are so sharpened 

 that he can follow every molecule in its course, such a 



1 Theory of Heat, 3rd ed. p. 308. Longmans, 1872. 



