"Mr. Perkins gives the following explanation of this apparent discrepancy, by referring to the small effect produced by fulminating powder, compared to gunpowder, although many times more powerful; he supposes that the action of fulminating powder, however intense, does not continue sufficiently long to impart to the ball its full power. The explosion of gunpowder, although not so powerful at the instant of ignition, is nevertheless, in the aggregate, productive of greater effect than that of fulminating powder, because the subsequent expansion continues in action upon the ball (but with decreasing effect), until it has left the barrel. The action of steam differs from either of these agents, inasmuch as it continues in full force until the ball has left the barrel; and to this is assigned the cause of its superiority.
"In the year 1826, Mr. Perkins had so perfected the mechanism of the gun and generator that, at an exhibition and trial of its power, in the presence of the Duke of Wellington and other distinguished officers of the Ordnance Department, balls of an ounce weight were propelled, at the distance of thirty-five yards, through an iron plate one-fourth of an inch in thickness; also, through eleven hard planks, one inch in thickness, placed at distances of an inch from each other. Continuous showers of balls were also projected with such rapidity, that when the barrel of the gun was slowly swept round in a horizontal direction, a plank, twelve feet in length, was so completely perforated, that the line of holes nearly resembled a groove cut from one of its ends to the other.
Fig. 370.
Perkins's steam gun.
"a is an iron furnace, containing a continuous coil of iron tubing, 80 feet in length, 1 inch of external and 5/8th inch of internal diameter, within which the fire is made; the upper end of this tube, b, called the flow-pipe, is extended any required distance to the top of the generator.
"The furnace is provided with a very ingenious heat governor or regulator, by which the intensity of the fire is always proportionate to the temperature which it may be requisite to maintain in the tubes.
"h is an iron box, containing a series of levers, b b b; c, a nut screwed upon the flow-pipe, and in contact with the short arm of the lowest of the levers. e. A lever, from one end of which is suspended the damper f, and from the other end the rod g, which rests upon the long arm of the highest of the levers, b b b. When the apparatus has arrived at the required temperature, the nut c is screwed down until it bears upon the lever. Any farther increase of temperature will expand or lengthen the flow-pipe, and depress the short arm of the lever, which is in contact with the nut. The combined and multiplied action of the levers will then elevate the rod g, and the damper f will descend to check the draught. When the fire slackens, and the apparatus cools, the action of the levers will be reversed, and the damper will open. The space through which the damper moves, compared with the nut c, is as 200 to 1.