At Fort Wagner, a sand work built during our war, Gen. Gillmore
estimated that he threw one pound of metal for every 3.27 pounds of
sand removed. He fired over 122,230 pounds of metal, and one night's
work would have repaired the damage. The new fifteen inch pneumatic
shell will contain 600 pounds of blasting gelatine, and judging from
the German experiments at Kummsdorf, which I have cited, one of these
fifteen inch shells would throw out a prodigious quantity of sand;
either 500 pounds to one of shell, or 2,000 pounds to one of shell,
according as the estimate of Gen. Abbot or of Capt. Zalinski is used.
The former considers that the radius of destructive effect increases
as the square root of the charge; the latter that the area of
destructive effect for this kind of work is directly proportional to
the charge.

The effect of the high explosives upon horizontal armor is very great;
but we have yet to learn how to make it shatter vertical armor. No
fact about high explosives is more curious than this, and there is no
theory to account for it satisfactorily. As previously stated, the
French have found that four inches of vertical armor is ample to keep
out the largest melenite shells, and experiments at Annapolis, in
1884, showed that masses of dynamite No. 1, weighing from seventy-five
to 100 pounds, could be detonated with impunity when hung against a
vertical target composed of a dozen one inch iron plates bolted
together.

In conclusion, I may say that in this country we are prone to think
that the perfection of the methods of throwing high explosives in
shell is vastly in favor of an unprotected nation like ourselves,
because we could easily make it very uncomfortable for any vessels
that might attempt to bombard our sea coast cities.