of the more refrangible solar rays. 137 



cut into two equal parts, of which one was placed under the 

 blue glass, and the other under a white glass, as nearly at 

 the same time as possible ; but the one did not become black 

 sooner than the other ; nor on comparing them could any 

 difference be perceived in intensity of colour, both having 

 been equally exposed to the chemical rays. The experiment 

 was repeated with the same result. 



On the 26th of August, the thermometer at noon being 

 es"", two neutral pieces of clock spring were exposed to the 

 sun, one under a thicker piece of the same blue glass, as in 

 the former experiment, and the other under green glass ; 

 both acquired polarity. 



31st of August, the thermometer at noon 68®. Having 

 thus succeeded in producing magnetism under the circum- 

 stances described, I next tried the effect of exposing neutral 

 pieces of clock spring to the sun, enveloped in violet and 

 green silk. The half of each was covered with paper as 

 before, and the pieces of spring then wrapped, one in green,- 

 and the other in violet-coloured ribbon, were fixed to the 

 inside of a pane of glass in a window, where they were left 

 exposed to the sun all day ; in the evening both had become 

 magnetic, although they were two of the pieces of spring 

 already said to have acquired polarity more slowly from 

 having been heated ; and as before, the parts exposed to the 

 sun under the ribbon were north poles. 



To learn if heat had any share in producing magnetism jn 

 this case, I exposed three pieces of the same steel to a bright 

 sunshine, on the 1st of September, the thermometer at noon 

 being at 70° : one half of each was covered with paper, but 



MDCCCXXVI. T 



Xy 



