OF GLASS, AND THE EESISTANCE OF GLASS VESSELS TO COLLAPSE. 225 
would rise in the globe, compressing the air in its interior, progressively, up to the 
point at which the resistance of the glass was overcome by the expansive force of the 
fluid ; at that point explosion would take place, the pressure in pounds per square inch 
being noted both by the eye of the observer and by the maximum Anger of the gauge. 
Fig. 7. 
In glass globes generally, the upper half of the sphere a, h, c (flg. 6) is the most 
spherical, and is approximately uniform in thickness, being however thinnest at b, and 
thickening gradually downwards towards the stem, the lower half (a, d, c) being consider- 
ably the strongest. Hence it happened, in several cases (in fact in every case in which 
the point could be determined with certainty from the condition of the fragments), that 
the globes ruptured first at h, the lines of fracture radiating in every direction, passing 
round the globe as meridians of longitude, and splitting it up into thin bands, varying from 
-^th to -g-th inch in width. In the case of some elongated ellipsoids, it appeared that 
the fractures occurred horizontally, or perhaps obliquely, from the condition of the frag- 
ments attached to the stem. In most cases, however, it was not clear from the frag- 
ments which had been the direction of the fracture, although the mode of rupture was 
the same in every case. 
To ascertain the thickness, several specimens were selected from the thinnest frag- 
ments, and each being measured separately by a micrometer screw of flfty threads to 
