218 T. Gaffield on the action of Sunlight on Glass. 
month, a piece is withdrawn from ex osure, carefully cleaned, 
and marked either with a diamond or by an adhesive label, and 
laced in the box. As “order is heaven’s first law,” it is pecu- 
time will be saved, and at the conclusion of an experiment, 
everything is in shape for exhibition to friends at home, oF 
students at a lecture room. 
Of course a perfect arrangement could only be made when a 
perfectly flat roof or platform in an open field could be provided, 
and the sunlight could act with full force during every hour aa 
minute of the day. But mine was sufficiently near this point to 
ow very interesting results. f 
In one of my earliest experiments, I kept a record of the 
ges going on in the various kinds of glass, at first from day 
to day, and afterwards from week to week, and month to month. 
The following is a specimen: 
Original color { Color after one Here 
> 
: 1 j ra’ 
bei Setieng *t, (3 mos.) 
before exposure. |day’s exposure.) other columns to exp’t. (3m pews 
ri give the names of all the different kinds of glass 
which Aave exposed to sunlight, but I refrain because for the 
poten given previously, I have found different specimens from 
© same ry of plate, of crown, and eet-glass, 
. 
sometimes to differ in shade, sometimes in result of expost!® 
etimes in 
“som 
~ I will however. give below. (not namin ‘oular mat 
Mio > gr . g the particular 
factories), a general description of my ex itt apres in 1868, 
when an exposure of thirty-three specimens for a few months i0 
mer and autumn showed the following results. 
