with water, the side of which ditch is lined or faced with a masonry wall of six to ten feet thick, behind and against which rises another sand-hill (the rampart) to the height of thirty-four feet above low water, and behind and below which is additional armament of heavy guns. Behind and below this last sand-hill (rampart) is the bomb-proof barrack, the eaves of which are thirty-one feet above low water, and three feet below the crest of the rampart which entirely surrounds this barrack. The walls of this building, occupied as a barrack by the garrison, are four feet thick, no part of which can be seen from the water, or be struck by any projectile than that of curved fire. The blast of a large quantity of powder is relied upon to ascend this sand-hill, pass over the ditch, and then descend into the body of the fort, strike and demolish the four feet walls of the barrack, and bury the garrison in its ruins. If its power can be relied upon to descend into the body of the fort, where alone it can injure the garrison who may choose to seek its protection, it would previously have descended into the ditch, and there harmlessly expended its force. I can find no reason to believe that these solid masses, or sand-hills, and massive walls, distant more than 450 yards from the site of the powder explosion, are to be removed or destroyed, or in any way injuriously acted upon by the air or atmosphere as a projectile, propelled by the explosion of any quantity of powder. All our experience goes to show that the atmosphere can only be used as a motive power by condensing it within circumscribed limits, and then giving vent to it, as in the air-gun, or by rapidly heating it within similar limits, and by sudden expansion act upon a solid in immediate contact, as the Ericsson engine. To put the air in motion and hope to batter and destroy any solid or substantial structure by any motion we can impart to the surrounding atmosphere, is contrary to our belief. The hurricane or tornado, combining the spiral with continued or prolonged action, we know to be capable of destroying vertical opposing surfaces of light structure, but such a continuous, prolonged action cannot be given to the atmosphere by any power within the control of man.
The power of the atmosphere put in motion and continued, during a moderate breeze, is 0.08 of an ounce on a square foot; during a fresh gale it is 5 pounds 3 ounces; during a hurricane [it] is 31.3 pounds, and during the most violent tornado, which destroys forests and wooden buildings and unroofs others, it is 46.1 pounds per foot, moving with a velocity of 97.5 miles per hour. Such a power, and the greatest we know of from a blast of wind, has never been known to disturb or injure such structures as those we are now considering. It is hoped to raise a breeze or hurricane at a distance of 450 yards from the object to be destroyed, by suddenly and momentarily upheaving the atmosphere at a point, without any means of conducting its force to the desired objects, which force when it arrives at the distance of a quarter of a mile has to be vastly greater than wind or the atmosphere has ever been known to move. We have some facts connected with the expansive force of gunpowder bearing upon this point. When confined to the bottom of the bore of a gun, say a 42-pounder, its expansive power is about 36,420 pounds on the square inch; give it, however, an air space of fourteen inches, or that distance in which to expand its power, and its force is but 15,850 pounds on the square inch; and give it still more space, forty-two inches, in which to expand itself, and the force is but 6,470 pounds on the square inch, thus decreasing its expansive power from 36,420 pounds to 6,470, or 29,950 pounds, in the short distance of forty-two inches, and that in the confined space of the bore of a gun.