T. Gaffield on the action of Sunlight on Glass. 247 
7 In accordance with the intention above expressed, I have con- 
unued my experiments on this interesting subject, and under 
different heads will now give some account of their method and 
results, 
first experiment was with pieces of glass four by six 
Inches, placed in a sash six by sixty inches long, in the grooves 
of which the specimens were placed, the sash being fastened 
together by wooden pins, and placed on a nearly horizontal 
tough plate-glass roof, which received the direct rays of the sun 
during the greater part of the day. In my next experiment, I 
aa some of the specimens directly on the rough plate-glass. 
hese were carried on in summer and autumn. It was neces- 
Sary to m : 
) fall of snow and the formation of ice might interfere with the 
+ _ full success of the experiments. I concluded that the best size 
being of greater depth in which to place pieces of plate and 
Tough plate about ahs inch in thickness. All of these boxes 
are provided with covers, which are placed over the glass, and 
ned by buttons, on the occurrence at any time of a snow 
Storm. At all other times, the glass is exposed. Holes in 
18 precaution is necessary to prevent mistakes, when a com-. 
os tee cane 4 Pinds and colors, of exposed 
and unexposed specimens. In all cases, where an experiment 
8 to be eR with any description of glass, hg (4x2 
. as there is 
as 
