It is very fortunate that things happen to be as they are in the cosmos and that the action of a high explosive when exploding against a massive body is to rebound from that body on the line of least resistance. It is for this reason that more damage is not done by great explosions. One of the biggest explosions in the history of gunpowder manufacture occurred at Pleasant Prairie, Wisconsin, on the 9th of March, 1911, when it was estimated that a thousand tons of black blasting powder blew up. Glass was broken over a very wide area. Some glass was broken in Chicago, about fifty miles distant. But neither the walls nor the foundations of buildings were greatly disturbed even but a few miles from the explosion. In the village of Pleasant Prairie, at a distance of but two miles, although the buildings were very much damaged the inhabitants continued to occupy them. Early in the morning of July 30, 1916, a very large quantity, certainly several hundred tons, of high explosive materials blew up in New York Harbor, not far from Ellis Island. A large quantity of shrapnel ammunition and other ammunition went up in the blast, their fragments raining all over the surrounding water. There was but very little loss of life, and the actual material damage to buildings in Jersey City, Manhattan and Brooklyn was astonishingly small, except the loss from broken glass. Why is it, then, that so much glass is broken and at such long distances, while the foundations and walls of buildings suffer but little injury? Let me explain. When a quantity of high explosive detonates, a wave of atmospheric compression is sent outward in all directions by the explosion. It is, in fact, a huge sound wave, and moves exactly at the speed of sound--about eleven hundred feet per second. Of course, buildings or other structures or objects near enough to the explosion to be struck by the expanding gases themselves, or by the atmosphere immediately propelled forward by them like a projectile, may be destroyed, but the area over which this action occurs is so circumscribed that no great damage is apt to result at distances beyond a few hundred feet. However, the great sound wave may travel to a distance of many miles. Consequently, as a result of the explosion just referred to, about a million dollars' worth of glass was broken in New York City alone. One would naturally suppose that the fragments of window glass broken in this manner would fall inside a building, but they do not. Almost always they fall outside into the street. The reason for this is that the wave of compression, striking a pane of glass, forces it inward nigh to the breaking point, and then as the wave of compression moves on, followed by a partial vacuum, the glass, springing outward to fill the void, breaks, and falls into the street.