THE EOYAL ARTILLERY INSTITUTION. 
157 
(in width and depth) as they approach the top and bottom of the shell. 
These grooves form so many “ lines of least resistance,” along which the 
bursting charge takes effect, thus acting, “ as it were, from the outside of the 
mass of balls,” 2 3 and so preserving the balls from the direct action of the 
bursting charge and opening the shell into five or more large pieces. 
But while the shell is weakened in the directions indicated by these 
grooves it is strengthened in another direction, for the following reasons: 
as the shell will inevitably burst at the line of least resistance, wherever that 
may be, it is evident that if there were a greater tendency to fracture at any 
part of the shell than in the direction of the grooves, the effect of the 
grooves would be, as it were, neutralized, these being no longer lines of 
least resistance; now, there is naturally, from the fact of the four little flanges 
by which the Diaphragm is supported being cast into the metal of the shell, 
and from the resistance offered by these flanges to the action of the powder, 
a great tendency to fracture round the line of junction of the Diaphragm, 3 
—-a greater tendency to fracture, that is to say, than in the direction of the 
grooves, if a special arrangement be not made to guard against it. The 
necessity for so guarding against it will be fully recognized if the effect of a 
separation round the line of junction is clearly perceived, viz. that the upper 
part of the shell would be liable to be blown off, thus either failing to 
release the bullets or injuriously affecting their flight. 4 
Two remedies, or arrangements, suggested themselves, viz. either to 
increase the depth of the grooves; or to reduce the strength of the flanges to 
a minimum, consistently with the security of the Diaphragm, at the same 
time thickening the metal of the shell round the line of junction; the second 
remedy was preferred to the first, which “ would have weakened the shell, and 
made it less capable of withstanding the shock of a heavy charge,” 5 and in 
2 Remarks on Diaphragm Shrapnel Shell, p. 10. The diagram here given is taken from Colonel 
Boxer’s Remarks on Diaphragm Shrapnel Shell, fig. 3, and is a copy of a photograph taken of 
“ a shell burst with the regular bursting charge.” 
3 “ It was found from the resistance which was offered to the action of the bursting charge by the 
cast-iron projection below the diaphragm that there was a great tendency to fracture through the 
line of junction.”— Ibid. p. 39. 
4 “ The explosion of the bursting powder would separate the shell at the part where the wrought- 
iron partition joins the interior surface, and the bullets would either not be relieved in the shell, or 
would be affected more or less in then’proper course according to the relative positions of the powder 
and the bullets at the moment of explosion, and the force of the explosion itself.”— Remarks on 
Diaphragm Shrapnel Shells. Appendix , 5 Ibid p. 39. 
