EPOCH OF YO.UXG AXD FRESXEL. Ill 



For, as I have said, the theory professes only to explain the pheno- 

 mena of radiant visible light. We know very well that light has 

 other bearings and properties. It produces chemical effects. The 

 optical polarity of crystals is connected with the chemical polarity of 

 their constitution. The natural colors of bodies, too, are connected 

 with their chemical constitution. Light is also connected with heat. 

 The undulatory theory does not undertake to explain these properties 

 and their connexion. If it did, it would be a Theory of Heat and of 

 Chemical Composition, as well as a Theory of Light. 



Dr. Faraday's recent experiments have shown that the magnetic 

 polarity is directly connected with that optical polarity by which the 

 plane of polarization is affected. When the lines of magnetic force 

 pass through certain transparent bodies, they communicate to them a 

 certain kind of circular polarizing power ; yet different from the cir- 

 cular polarizing power of quartz, and certain fluids mentioned in 

 chapter ix. 



Perhaps I may be allowed to refer to this discovery as a further 

 illustration of the views I have offered in the Philoso})hy of the In- 

 ductive Sciences respecting the Connexion of Co-existent Polarities. 

 (B. v. Chap, ii.)] 



CHAPTER XII. 



S3QUEL TO THE EPOCH OF YOUXG AXD FRESXEL. RECEPTION OF 

 THE L^XDULATORY THEORY- 



1T7"IIEN Young, in 1800, published his assertion of the Principle of 

 *' Interferences, as the true theory of optical phenomena, the con- 

 dition of England was not very favorable to a fair appreciation of the 

 value of the new opinion. The men of science were strongly pre-oceu- 

 pied in favor of the doctrine of emission, not only from a national 

 interest in Newton's glory, and a natural reverence for his authority, 

 but also from deference towards the geometers of France, who were 

 looked up to as our masters in the application of mathematics to phy- 

 sics, and who were understood to be Newtonians in this as in other 

 .subjects. A general tendency to an atomic philosophy, which had 

 begun to appear from the time of Newton, operated powerfully ; and 



