Sir H. Davy on Electrical and Chemical Changes. 31 



So far as the case of the present eclipse bears upon the ques- 

 tion, I tried this with respect to the extreme red rays dis- 

 covered by Mr. Herschel, to which the greatest heating power 

 belongs ; and looking at the sun during the eclipse through a 

 good prism of flint glass, interposing before the eye three 

 thicknesses of the purple glass, described by that gentleman, 

 I saw the ray in question perfectly distinct, and unaltered as 

 compared with its appearance when there was no echpse. 



The deep red image of the sun thus forming the end of the 

 spectrum, of course exhibited the eclipse ; and in a spectrum 

 formed in a darkened room, if the superposition was but 

 small, the same deficiency at the red end might be apparent; 

 but this obviously would not explain a deficiency of heat as 

 compared with that of the compound rays ; nor would it ac- 

 count for the increased brilliancy which Mr. Wiseman ob- 

 served in the yellow and blue. 



I am not aware what was the cause reasoned upon by Mr. 

 W. as capable of producing any actual relative deficiency of 

 red rays : if it were any such cause as inflexion of the sun's 

 light in passing the body of the moon, which should affect 

 the red rays most, and thus the light reaching the earth 

 should be deprived of a portion of red, a less portion of 

 green, blue, &c. this would produce a diminution in intensity, 

 though not a deficiency in space, in the red part of the spec- 

 trum. Hence, however, would result a greater relative bright- 

 ness in the blue, &c. ; and such a difference in the heating 

 effects as has been described. Such a cause would act more 

 sensibly in porportion to the magnitude of the eclipse; and its 

 effects might be quite insensible, except in a very considerable 

 eclipse. 



X. The Bakerian Lecture. On the Relations of Electrical 

 and Chemical Changes. By Sir Humphry Davy, Bart. 

 Pres. R.S.* 



I. Introduction. 



A LONG time has elapsed since I read before this Society 

 -^^ the Bakerian Lecture on the Chemical Agencies of Elec- 

 tricity. The general laws of decomposition developed in that 

 paper were immediately illustrated by some practical results, 

 which the Society did me the honour to receive in a very fa- 

 vourable manner ; and which, by offering a class of new and 

 powerful agents, led rne away for many years into a field of 



* From the Philosophical Transactions for 182G. Part III. 



pure 



