The Mexican War was a school of artillery practice and marked a distinct era of progress. The flying artillery of Ringgold, in the field, and Perry’s siege guns, in the naval battery at Vera Cruz, were revelations to Europe of the great advance made by Americans in this branch of the science of destruction. In the Civil War, on land and water, the stride of centuries was taken in four years, when Dahlgren introduced that “new era of gun manufacture which now interests all martial nations.” Since then, the enormous guns of Woolwich and Krupp have come into existence, but perfection in heavy ordnance is yet far from attainment. Much has been done in improving details, but the original principle of gun architecture is still in vogue. The loss of pressure between breach and muzzle is not yet remedied. To build a gun in which velocity and pressure will be even “at the cannon’s mouth” is the problem of our age. When a ball can leave the muzzle with all the initial pressure behind it we may look for the golden age of peace: such a piece of ordnance may well be named “Peace-maker.” This problem in dynamics greatly interested Perry; but foiled him, as it has thus far foiled many others. The School of Gun Practice was opened again in the spring of 1840. He was now experimenting with an eight-inch Paixhans gun, and comparing with it a forty-two pounder, which had a bore reamed up to an eight-inch calibre. Not possessing the present delicate methods of measuring the velocity of shot, such as the Boulanger chronograph, invented in 1875, and now in use at the United States ordnance grounds at Sandy Hook, he obtained his measurements by means of hurdles or buoys. After their positions had been verified by triangulation, these were ranged at intervals of 440 yards apart along a distance of 3¼ miles. Observers placed at four intermediate points noted time, wind, barometer, etc. The extreme range of a Paixhans shot was found to be 4067 yards, or about 2-1/3 miles. In transmitting eight tables, with his report he stated that “These experiments have furnished singular and important information.” After a summary of unusual, interesting and valuable work, the school was closed November 23, 1840, the weather being too severe for out-door work.