SOLAR INFLUENCE. 263 



ever, required, before we can decide satisfactorily either 

 of these problems, both of which bear very strongly 

 upon the subject we have just been considering. 



We have seen that heat and electricity act strangely on 

 magnetic force, and that this statical powej reacts upon 

 them : and thus the question naturally arises, Do light 

 and magnetism in any way act upon each other ? 



Morichini and Carpi on the continent, and Mrs. 

 Somerville in England, have stated that small bars of 

 steel can be rendered magnetic by exposing them to 

 the influence of the violet rays of light. x These results 

 have been denied by others, but again repeated and 

 apparently confirmed. In all probability, the rays to 

 which the needles were exposed, being those in which 

 the maximum actinic power is found, produced an 

 actual chemical change ; and then, if the position were 

 favourable, it is quite evident that magnetism would be 

 imparted. Indeed we have found this to be the case 

 when the needles, exposed to solar radiations, were placed 

 in the direction of the dip. The supposed magnetization 

 of light by Faraday has already been mentioned. If 

 the influence in one case is determined, it will render 

 the other more probable.* 



" In seeking for a cause," writes Sir David Brewster, 

 " which is capable of inducing magnetism on the ferru- 

 ginous matter of our globe, whether we place it within 

 the earth, or in its atmosphere, we are limited to the 

 SUN, to which all the magnetic phenomena have a dis- 

 tinct reference ; but, whether it acts by its heat, or by 

 its light, or by specific rays, or influences of a magnetic 

 nature, must be left to future inquiry.'^ 



* See a notice by Faraday of Morichiui's Experiments in 

 Relations of Light to Magnetic Force Philosophical Transactions, 

 vol. exxxvii. p. 15. See also Mr. Christie On Magnetic Influence 

 in the Solar Rays Philosophical Transactions, voJ. cvii. p. 219 ; 

 vol. cxix. p. o79. 



f Sir David Brewster On Magnetism', republished from the 

 Encyclopaedia Britannica. 



