244 ME. W. EAIEBAIEN A4s^D ]\IE. T. TATE OX THE MECHAXTOAL PEOPEETIES 
mined by equation (3.) ; hence we find 
0=11^=740,000. 
. 011-4 
Substituting these values of the constants in equation (2.), we get 
P=740,000 ^, (12.) 
which is the general formula for calculating the strength of glass cylinders subjected to 
external pressure, within the limits indicated by the experiments, that is, provided then- 
length is not less than twice their diameter, and not greater probably than six times 
their diameter. This law of strength is precisely similar to that foimd for sheet-iron 
tubes. 
For convenience of calculation, this formula may be written 
logP=3-06923+l-41og(100^)-log(DL) (13.) 
The following Table will show how nearly formula (12.) represents the results of the 
experiments on glass cylinders : — 
Table XII. — Eesults of Experiments on the Eesistance of Glass Cylinders 
to External Pressure. 
Number of 
experiment. 
D. 
L. 
k. 
P 
by experi- 
ment. 
P 
by formula. 
Proportional 
error by ! 
formula. 
XI. 
3-09 
14 
•024 
85 
86 
XII. 
3-08 
14 
•032 
103 
138 
+ 1 
XIII. 
3*25 
14 
•042 
175 
192 
+i 
XIV. 
4-05 
7 
•034 
202 
227 
+tV 
XV. 
4*05 
7 
•046 
380 
351 
1 
1 1 
XVI. 
4-06 
13-8 
•043 
180 
161 
i. 
XVII. 
4-02 
13-8 
•064 
297 
284 
1 
2lS 
XVIII. 
3-98 
14 
•076 
382 
361 
_ 1 
T? 
XIX. 
4-05 
7 
•079 
500 
747 
Unbroken. 
XX. 
4*2 
22 
•055 
120 
138 
+ i 
XXI. 
4-1 
21-5 
•051 
129 
130 
+ TYV 
XXII. 
4-2 
22 
•0455 
125 
107 
— i 
Comparative Strength of Glass and Sheet-iron Cylinders subjected to an External 
Pressure tending to produce Collapse. 
The formula of strength for sheet-iron cylinders, after reducing L to inches, is 
F=806,300xl2x|^. 
laiJ 
Now for cylinders of the same diameter, length, and thickness, we find, by di\iding 
equation (12.) by the above, 
P _-0764 
P'~ /f79 ■ 
( 14 .) 
