In an interesting address by Major Clarence E. Dutton of the Ordnance Department, U.S.A., at the Centennial Patent Congress at Washington in 1891, he thus stated what the fundamental improvements were that have characterised the modern ordnance during the century: 1. The regulation and control of the action of gunpowder in such a manner as to exert less strain upon the gun, and to impart more energy to the projectile. 2. To so construct the gun as to transfer a portion of the strain from the interior parts of the walls which had borne too much of it, to the exterior parts which had borne too little, thus nearly equalising the strain throughout the entire thickness of the walls. 3. To provide a metal which should be at once stronger and safer than any which had been used before. In the United States General Rodman, “one of the pioneers of armed science,” commenced about 1847 a series of investigations and experiments on the power and action of gunpowder and the strains received by every part of the gun by the exploding gases, of very great importance; and in this matter he was assisted greatly by Dr. W. E. Woodbridge, who invented an ingenious apparatus termed a “piezometer,” or a pressure measurer, by which the pressure of the gases at the various parts of the gun was determined with mathematical certainty. Dr. Woodbridge also added greatly to the success of rifled cannon. The success in rifling small arms, by which an elongated ball is made to retain the same end foremost during its flight, led again to the attempts of rifling cannon for the same purpose, which were finally successful. But this success was due not to the spiral grooves in the cannon bore, but in attachments to the ball compelling it to follow the course of the grooves and giving it the proper initial movement. The trouble with these attachments was that they were either stripped off, or stripped away, by the gun spirals. Woodbridge in 1850 overcame the difficulty by inventing an improved _sabot_, consisting of a ring composed of metal softer than the projectile or cannon, fixed on the inner end of the projectile and grooved at its rear end, so that when the gun is fired and the ball driven forward these grooves expand, acting valvularly to fill the grooves in the gun, thus preventing the escape of the gases, while the ring at the same time is forced forward on to the shell so tightly and forcibly that the projectile is invariably given a rotary motion and made to advance strictly in the line of axis of the bore, and in the same line during the course of its flight. This invention in principle has been followed ever since, although other forms have been given the sabot, and it is due to this invention that modern rifled cannon have been so wonderfully accurate in range and efficient in the penetrating and destructive power both on sea and land.