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42 INTERNATIONAL EXHIBITION, 1876. loading may differ, the main conditions upon which the power of the guns depends—namely, velocity, penetration, and accuracy—must be secured. At present the most prominent methods of constructing heavy ordnance in Europe are three in number: the English, the French, and the German. In the English, or Woolwich muzzle-loading system, the gun is built up of a strong, solid-ended steel tube, surrounded by several double or triple wrought-iron coils. It is claimed that this method of construction produces the safest, cheapest, and simplest system of heavy ordnance. The guns are said to be the most powerful of their class, and to possess the great merit of non-liability to burst explo sively,—the failure of a gun being preceded by timely warnings to the gun detachments. The French breech-loading system of construction (modele 1871) consists of a cast-iron tube, reinforced from the breech about one- third of its length by a steel tube, and strengthened over the breech, as far as the trunnions, by superimposed rings of puddled steel. Thus the breech of the gun, where the strength is required, is fortified by an inner steel tube and outer steel rings, and the chase is simple cast- iron, unstrengthened. The German or Krupp breech-loading method of construction has been very fully detailed in the report on the Vienna Exhibition. It consists of a steel tube surrounded by superimposed steel rings. It would be impossible without a practical competitive trial to form an opinion as to the relative merit of these three systems, or to decide which country has the best armor-piercing gun. It is only possible to produce figures, drawn from the most trustworthy sources at our command, and arranged in the most convenient form. The comparative merit of armor-piercing guns is deduced on paper from the weights of the projectiles which they throw, and the velocity with which these projectiles strike the object at which they are di rected. The blow thus struck is proportional to what in scientific language is termed the “ energy” of the projectile at impact. The numerical value of this quantity is found by multiplying the weight of the projectile in pounds by the square of the velocity on impact in feet, and dividing the product by twice the force of gravity in feet,—or As a matter of convenience it is usual to express the result in foot tons, and as there are 2240 pounds in a ton, equation (1) becomes IIV
