AND THK THEORY 01' LIGHT. 7 



aid in tracing the true theory of heat^ magnetism and 

 the other imponderables. 



7. But there are other questions respecting the physical 

 nature of light than the decision of the truth of the cor- 

 puscular or undulatory theory. It is equally important to 

 know whether it be a homogeneous or a heterogeneous 

 substance. The grand discovery of comparatively modern 

 times is that of the heterogeneous nature of light ; and the 

 facts discovered seem to adapt themselves to, and to be 

 explicable by either theory, for like mathematics, in the 

 opinion of some writers, the compound nature of light 

 is consistent with either theory. But surely it is more 

 than a matter of idle curiosity to decide this question. If 

 light could be proved to be a simple substance, the theory 

 would be rendered more conformable to the recognized 

 simplicity of nature's laws, and would thereby commend 

 itself more to the human intellect, which estimates the 

 divine authority of a law by the universality of its appli- 

 cation and its simplicity. The sublimity of the law of 

 gravitation lies in these two qualities — its universality 

 and its simplicity. 



8. I have already remarked that, from the discrepancy 

 that exists among philosophers as to the composition of 

 light, there is room for a new investigation into the cause 

 of colour. In the present day however, such an investiga- 

 tion could not be made by means of any refracting medium. 

 Refracting media are already explained, or believed to be 

 explained, on arguments conventionally acquiesced in as 

 established truths, or at all events, as truths which it would 

 be presumptuous in any one in this era of philosophy to 

 question, either by logical or mathematical reasoning. 



I propose therefore 



I. To give the result of my study of the laws of light 

 without the aid of any refracting substance. 



