T. Gaffield on the action of Sunlight on Glass, 319 
1 . been exposed in the same way without any change of color, ex- 
} cepta very slight one in a few specimens which were burnt or 
, as, . 
the surrounding portions having been changed by the action of 
the sunlight to a purple color. 4 
very interesting experiment can be made, to show the grad- 
ete! 
