137 
of the more refrangible solar rays. 
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 
66 °, 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 in 
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 
