2 MR. J. SMITH ON THE ORIGIN 01-' COLOUR 



physical principles is another. Should a physical pheno- 

 menon assume a geometrical form, a mathematician may 

 argue upon it and draw from it some valuable infer- 

 ences without understanding more than the geometry of 

 the phenomenon. The reasoning from the premises may 

 be strictly correct, the deductions mathematically sound, 

 and still the conclusions far from being physically true. 

 The reasoning being founded on geometrical, not on phy- 

 sical facts, only explains such phenomena as are described. 

 Hence the general dissatisfaction with the theory of the 

 different refrangibilities of the rays of light as unfolded 

 by prismatic refraction. The theory resolves itself into 

 the geometrical description of a physical phenomenon, it 

 affords no explanation of the physical process ; and as far 

 as the analysis of the physical process is concerned, it is 

 chiefly an attempt to prove that because a ray, after being 

 once refracted, cannot be changed by repeating the same 

 process, it is to be inferred that the ray is reduced to 

 its simple elements ; thus assuming, not proving, that the 

 prism is an analytical instrument. 



2. To the general student a subject is supposed to be 

 made clear when it is described in mathematical language 

 assisted by geometrical diagrams. But there is nothing 

 in which we are more apt to deceive ourselves, in studying 

 science, than in mistaking the knowledge of the language 

 in which a phenomenon is described for a knowledge of 

 the physical laws, on which the phenomenon depends ; 

 and in the study of nature we often deceive ourselves 

 by generalizing without sufficient investigation; for like 

 the student of science the student of nature is apt to mis- 

 apprehend the language in which nature speaks ; he not 

 unfrequently mistakes geometrical laws for physical, and 

 explains the one by the other. He begins to generalize 

 when he discovers that physical laws are in accordance 

 with some of the rules of his previously acquired geo- 



