2 
Dr. Brewster’s additional observations on the 
a crystalline structure. Upon examining the bulb of an un- 
annealed drop AB, PI. I., fig. 1, by holding it between the 
eye and a sheet of white paper, I observed a number of lines 
converging to the vertex a , as represented in fig. 2. This 
structure was more or less apparent in every bulb which I 
examined, but never appeared in annealed drops. It exhibited 
itself even on the surface, and seemed to be owing to an im- 
perfect crystalline form, yet it was not marked with sufficient 
distinctness to entitle me to consider it as the effect of crys- 
tallization. In one specimen, however, where the bulb AB 
remained unshattered, while all the rest of the drop was burst 
in pieces, the lines diverging from a were most distinctly 
marked, and the bulb was actually cleft in the direction of 
these lines, so as to produce a real dislocation at the surface 
of the drop. We may therefore consider the drop as possess- 
ing that crystalline structure which gives cleavages in the 
direction of lines diverging from its apex. By examining the 
fragments of the drop after it is burst, another cleavage is 
distinctly perceptible : it is parallel to the outer surface, and 
produces a concentric structure like that of an onion. This 
cleavage also shows itself in the splinters which are de- 
tached from the surface of the drop when it is ground upon 
freestone. A third cleavage is visible in the direction of lines 
inclined to the axis of the drop, as represented in fig. 3 ; but 
it is not so distinct as the two first. 
As it appeared probable that the glass drops possessed a 
less degree of density than if they had been annealed, I at- 
tempted to ascertain this point by measuring their specific 
gravities in these two different states. The unannealed drops, 
however, had always one or more vacuities, such as E, F, 
