NOTES TO BOOK X. GO! 



not a single Inductive Science, but the application of 

 several sciences to the explanation of terrestrial and atmo- 

 spheric phenomena. Of the sciences so applied, Ther- 

 motics and Atmology are the principal ones. But others 

 also come into play; as Optics, in the explanation of 

 Rainbows, Halos, Parhelia, Coronse, Glories, and the like; 

 Electricity, in the explanation of Thunder and Lightning, 

 Hail, Aurora Borealis ; to which others might be added. 



(VA.) p. 588. Since the first edition was written, the 

 analogies between light and heat have been further ex- 

 tended. It has been discovered by MM. Biot and Melloni 

 that quartz impresses a circular polarization upon heat ; 

 and by Prof. Forbes that mica, of a certain thickness, 

 polarizes heat circularly ; and further, a rhomb of rock- 

 salt, of the shape of the glass rhomb which verified Fres- 

 neFs extraordinary anticipation of the polarization of light, 

 verified the expectation, founded upon other analogies, of 

 the polarization of heat. By passing polarized light through 

 various thicknesses of mica, Prof. Forbes has attempted to 

 calculate the length of an undulation for light. 



These analogies cannot fail to produce a strong dis- 

 position to believe that light and heat, so closely connected 

 that they can hardly be separated, and thus shown to have 

 so many curious properties in common, are propagated by 

 the same machinery ; and thus we are led to an Undula- 

 tory Theory of Heat. 



Yet such a Theory has not yet by any means received 

 full confirmation. It depends upon the analogy and the 

 connexion of the Theory of Light, and would have little 

 weight if those were removed. For the separation of the 

 rays in double refraction, and the phenomena of periodical 

 intensity, the two classes of facts out of which the Undu- 



VOL. ii. RR 



