ON THE COLLAPSE OF GLASS GLOBES AND CYLINDERS. 175 
by a Scheffer gauge. The point of rupture was indicated by an explosion 
within the vessel, and by the sudden decrease of pressure. 
The first experiments were upon glass globes, intended to be perfectly 
spherical, but in most instances somewhat flattened upon the side opposite 
to that from which they were blown. Notwithstanding, however, this ellip- 
ticity, some of the globes bore enormously high pressures, especially when 
the extreme tenuity of the glass is considered, amounting to from one to 
- two hundredths of an inch in thickness only. 
Tas Le I.—Strength of Glass Globes to resist a uniform external pressure. 
Mark. Diameters. Thickness. | Collapsing pressure. 
inches. inch. lbs. per square inch. 
L 5:05 0-014 292 
M 5:08 0:018 410 
K 4:95 0:022 470 
B 5°60 0:020 475 
N 8:22 0:010 35 
Cc 8:20 0:012 42 
D 8-20 0-015 60 
It will be seen that, notwithstanding the extreme thinness of the glass, 
the pressures range as high as 475 lbs. per square inch over every square 
inch of surface, equivalent to a total pressure of 20 tons upon a 55-inch 
globe =,th of an inch thick, before it was fractured. 
Unfortunately the 8-inch globes were all elliptical to a serious extent, 
and hence in these the collapsing pressure was greatly reduced, ranging 
from 35 to 60 lbs. per square inch only. 
The next results are upon glass cylinders, blown with hemispherical ends. 
In the experiments upon iron, the remarkable law had been deduced that 
the strength of cylindrical vessels of that material, exposed to a uniform 
external pressure, varied inversely as the length. Thus with vessels precisely 
similar in other respects, one twice the length of another bore only half the 
pressure, one three times the length bore only one-third of the pressure, and 
so on. From the following experiments it will be seen that a similar law 
applies in the case of homogeneous glass cylinders. 
Tas ce II.—Strength of Glass Cylinders to resist a uniform external 
pressure. 
Mark. | Diameter.| Length. | 'Thickness.|Collapsing pressure per square inch, 
inches, inches. inch, lbs. 
E 06 132 | -043 180 
G 4-02 132 | -064 297 
H 3°98 14 ‘076 382 
1?) 4:05 <. “046 380 
Q 4:05 7 034 202 
T 3°09 14 024 85 
R 3:08 14 032 103 
iS) 3:25 14 042 175 
These cylinders, though of high resisting powers, sustain considerably less 
_ pressure than the globes. Comparing cylinders E and P, 14 and 7 inches 
‘long respectively, and of the same diameter and thickness of glass, we find 
the longer was crushed with about half the pressure which was requisite to 
collapse the shorter cylinder, which is a confirmation of the law deduced for 
iron tubes. 
