368 



Experiments on the Magnetic Influence of Solar Light. 

 By Lieut. R. Baird Smith, Bengal Engineers. 



[Continued from p. 264, vol. iii.] 



Section III. — On the Magnetic Influence of Solar Light, 

 transmitted through different coloured Media.* 



The only experiments on this branch of the subject of 

 Solar Magnetism with which I am acquainted, are those due 

 to Mrs. Somerville ; but as far as I have, up to the present 

 time, been able to ascertain, only two coloured Media, namely 

 green and blue, were employed by her, and both with suc- 

 cess. Needles exposed to the sun for three or four hours, 

 under a glass coloured blue by cobalt, were found to have 

 had imparted to them a feeble, but none-permanent, mag- 

 netism ; and in subsequent experiments, by extending the 

 period of exposure to six hours, a very distinct degree of 

 Magnetism was acquired and permanently retained. Green 

 glass was also tried, and was found to admit of the passage 

 of magnetic rays ; and needles suspended behind a window 

 pane, half covered with blue and green riband, were found 

 to have been equally strongly magnetised as when coloured 

 glass itself was employed. 



* It will furnish to European observers, a striking illustration of the 

 paucity of experimental resources in the remoter parts of British 

 India, when I state that up to the present time, although aided by the 

 kind and active efforts of friends, I have found it quite impossible to 

 procure, on any conditions, a common glass prism, to enable me to com- 

 plete the experiments of the second section. It is probable I shall 

 be obliged to procure such a piece of apparatus from England, and 

 in the mean time I cannot but fear that the opportunity of complet- 

 ing this section for at least a very long period, will be allowed to 

 pass. The completeness of the enquiry is of course interfered with by 

 the absence of the second section; but the first and third, are, at the 

 same time, perfect in themselves, and in no way dependant on its pre- 

 sence, so that it is of comparatively little moment, in what order they 

 are published,, It is impossible however to rest satisfied with the 

 present imperfect condition of what I meant to be a perfect examina- 



