THE ROYAL ARTILLERY INSTITUTION. 
423 
pressure, the strain due to which, as will be shown further forward in this report, 
must be considerably less than the actual strain, the rate of application of the force 
affecting the strain to which it subjects the resisting body so far as even to double 
it in the extreme case, or when the application of the force becomes instantaneous.” 
He conducted a much more elaborate and valuable series of experiments 
to ascertain in the very bore itself what was the actual pressure at each 
point. In order the better to judge of the value of his deductions, it is 
necessary to give a short account of some preliminary experiments which 
were made with hollow cylinders to test their strength. 
Major Wade gives the hydrostatic pressures necessary to burst cast-iron 
hollow cylinders cut from the chase of a 6-pr. gun, of one-quarter and one- 
half calibres thickness, compared with the tensile strength of the iron. - * 
Tons per 
Tenacity. square inch. 
By direct tensile force . 14-8 
t, i f Thickness equal to half a radius . 1T1 
By water pressure [ TMctuoss ^ to radius . 8-9 
Eropor* 
tion. 
1 
0742 
0-602 
These pressures agree so well with what might be expected from the law 
of decrease of proportionate strength as the thickness increases, that I have 
no hesitation in accepting them as correct. The law of decrease only holds 
strictly as far as the elastic limits up to which the extension is uniform; 
beyond the elastic limits the extension increases more rapidly than the 
strain. Thus there is a slight increase of the proportion of strength given 
when the thickness was one-half calibre, which by calculation would other¬ 
wise be equal to half the tensile strength of the metal. 
Bodman tested similar cylinders with gunpowder. The cylinders, like 
the last, had the column of metal in the walls of the same length as the 
bore on which the pressure acted. The length was 12 ins., and the calibre 
2 ins. The thickness of metal was varied. The following table shows the 
actual pressures measured when these cylinders were burst by powder ex¬ 
ploded in the interior. Alongside the actual pressures is given a set of 
pressures calculated according to the law which regulates the strength of 
hollow cylinders, and made to agree with the instance in which the thickness 
of metal was one-half calibre in Bodman's experiment, the particular thick¬ 
ness being chosen because it required two charges to burst it, and may 
therefore be considered as just burst, and no more. (See Eig. 3.) 
I have given Major Wade's hydrostatic bursting pressures for comparison. 
Thickness of metal. 
Mean bursting 
pressure by 
experiment. 
Computed 
bursting 
pressure. 
Hydrostatic 
bursting 
pressure. 
tons. 
tons. 
tons. 
0-5 in. 
. 16-9 
11*4 
5-5 
1*0 „ . 
17-1 
17-1 
8-9 
1*5 /, . 
28*3 
20-6 
_ 
2-0 „ . 
35-8 
22-8 
_ 
2-5 „ . 
41-2 
24-4 
3-0 /, . 
41-8 
257 
_ 
Tenacity . 
12-0 
— 
— 
* Reports of Experiments on Metals for Cannon, by Officers of the Ordnance Department U.S. 
Army. 
56 
