246 LT. Gaffield on the action of Sunlight on Glass. 
during the greater part of the day. In all cases, strips corres 
ponding to those exposed, and cut off from the same pieces, 
were placed in the dark, to be compared with the other speci- 
mens after exposure. 
“It will be noticed that the dark green, blue, and bluish green 
did not change. The color of the Belgian sheet (called German 
or French by glass-dealers in America), a yellowish or brownish 
green, did not change; and these were the only exceptions. 
All plate-glasses changed, except an inferior blue quality, anda 
superior crystal plate of a greenish color, made in Germany, 
and at the only factory which has not given up the use of pot- 
ash for soda-as 
“Tt is possible that a longer exposure of a year, or of years, — 
might change every color in some degree. 
“His inquiries, since he instituted these experiments, have 
to a golden and in others to the well-known urple hue. 
‘It is his intention to pursue the experiments farther, with a 
place much more rapidly than in the different and less clear 
atmosphere of England. 
. Some writers point to the presence of oxyd of manganese 
in the original composition of window-glass, and some to the 
classes of the sun’s rays. Some may think the change refer 
el om any explanation, waiting for a larger multiplication 
of experiments, and a greater accumulation of facts, before 
educing any satisfactory law of nature which governs thes? 
curious and interesting phenomena. 
BLA, UUUMA 
red thas 28 seg a his jmens t0 
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