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.

This is true as far as it goes, but unfortunately the use of high explosives will not stop there.  I lately had explained to me the details of a system which is certainly not impossible for damaging New York from the sea by means of dynamite balloons.  The inventor simply proposed to take advantage of the sea breeze which blows toward New York every summer’s afternoon and evening.  Without ever coming in sight of land, he could locate his vessel in such a position that his balloons would float directly over the city and let fall a ton or two of dynamite by means of a clock work attachment.  The inventor had all the minor details very plausibly worked out, such as locating by means of pilot balloons the air currents at the proper height for the large balloons, automatic arrangements for keeping the balloon at the proper height after it was let go from the vessel, and so on.  His scheme is nothing but the idea of the drifting or current torpedo, which was so popular during our war, transferred to the upper air.  An automatic flying machine would be one step farther than this inventor’s idea, and would be an exact parallel in the air to the much dreaded locomotive water torpedo of to-day.  There seems to be no limit to the possibilities of high explosives when intelligently applied to the warfare of the future, and the advantage will always be on the side of the nation that is best prepared to use them.