of Salem and Barramahal. 185 



fore, that the granite rocks have been formed by the fusion 

 and consolidation of the schistose beds ; but it will be quite 

 unnecessary to follow out the theory any further, as the 

 subject has been already sufficiently dilated upon by much 

 abler and better informed writers. 



The basalt veins and dykes in granite will also serve 

 to corroborate this theory, for they also occur in the schis- 

 tose series, most commonly in the shape of wall-sided dykes. 



On Solar Radiation. By Captain J. Campbell, Assistant 



Surveyor General. 



Solar radiation, or the heating power of the sun's rays, 

 is a subject on which very little is still known, and which 

 ought to receive more attention in India, where we have a 

 considerable range of latitude, a generally clear sky, and 

 opportunities for observation hardly equalled in any part 

 of the world. 



As I have not opportunities of regularly seeing the peri- 

 odical scientific publications, and the latest standard work I 

 have to refer to is of 1835 only, I shall therefore not at- 

 tempt to give an account of the present state of our know- 

 ledge on this subject, but confine myself to pointing out 

 the advantage of collecting experiments, and the mode 

 of making them; for which purpose it will be necessary 

 to commence with a sketch of the subject, for the sake of 

 explanation. 



In 1823, Daniel, in his Meteorological Essays, pointed out 



the difference of the heating powers of the sun's rays in 



different latitudes, as shewn by exposing to their full action 



a mercurial thermometer with the ball blackened. He 



compares the results obtained by Captain Sabine, himself, 



and Captain Scoresby in the Arctic regions, and shews that 



the utmost power of the sun's rays in different latitudes, only 



2 B 



