second, does not, at 2° of elevation, attain two-thirds of the range it would have in vacuo, the Armstrong, with an initial velocity of about 1,050 feet per second, exceeds it by about 120 yards.

From the above-mentioned obliquity of the elongated projectile to the curve of its flight, and the consequent unequal action of the resistance of the air above and below, arises a deviation in its flight, which is termed derivation; but this is constant for similar ranges, and can be allowed for.

We now come to a practical difficulty in the manufacture of large guns. This difficulty was found even in making round-shot guns of above eight inches in diameter of bore, strong enough to withstand the charge required to impart high velocities to solid shot; and with elongated shot this difficulty is greatly increased, because the weight of the projectile is increased in proportion to the size of the bore. For as was pointed out, we believe, first by Dr. Hutton, it is of no use to increase the thickness of metal in the gun beyond a certain point. Let us take the cross-section of a gun, that is to say, an annulus, and inquire, what is the precise action of the exploded powder on this? We know that iron in resisting a tensile strain is extended (a small portion of the extension, from want of perfect elasticity, being permanent), and the gun, or the portion of it which we are considering, the annulus, is therefore enlarged, this enlargement being, to a great extent, only momentary. But though it is enlarged, the area of the annulus, which, being the cross section, represents the amount of metal in the gun at that point, must remain the same; therefore the width must diminish; or, which is the same thing, the circumference of the inner circle must be increased in a greater ratio than the outer; i. e., the inside of the gun must be more stretched than the outside. Now, if we consider the annulus divided into its component concentric rings, the greater the distance of each successive ring from the centre, the less will it be stretched, the less will be the strain on it, and the less good will it do,-till we arrive at a point when the inside of the bore or inside ring will be ruptured, before any strain is taken by the outside; so that, beyond a ceertain point, increasing the thickness of the metal is useless.

In order to make the gun sufficiently strong, various means have been suggested (Captain Blakeley, some of whose guns were in the Exhibition, having been, we believe, one of the first and most successful in practically meeting the difficulty), such as shrinking or driving on rings of metal on an inner core, or by winding wire on it with an increasing strain, so that what is called an "initial tension" is given to the outside of the gun; and the successive rings of the annulus

in their normal state vary from a state of compression within to tension without; each part thereby bearing its own work-that is, when the strain comes on it, the whole thickness of the is serviceable in resisting it.

gun

We have now to consider the projectile. Windage, or the looseness of the bullet in the bore, for ease in loading, has been before adverted to, with the inaccuracies to which it gives rise. In the rifle, where the spherical bullet was used, there was necessarily no windage, for the bullet, in order to take the grooves, was (except in the two-grooved rifle with belted ball) forced down by a heavy ramrod and mallet. This difficulty in loading was, indeed, one of the main objections to the rifle. Breech-loaders and expanding bullets afford means of avoiding windage and yet loading easily.

The methods by which the modern cylindro-conical projectile is made to take the rifling, or fit the grooves of the gun, may be classed under three heads:

1. The mechanical fit, where the projectile is made of the exact form of the bore before being inserted in it. The projectile may be of hard metal throughout. This plan has been adopted by Mr. Whitworth, Mr. Lancaster, Captain Blakeley, and others, in England, and in all the foreign ordnance we have seen.

2. By making the projectile (which must, therefore, be at least coated with a soft metal) rather larger than the bore of the gun. It is inserted at the breech, which is enlarged to receive it, and it takes the rifling by being forced forward by the powder and crushed into the grooves. This plan is adopted by Sir William Armstrong,* and also in many breechloading small-arms.

3. By the projectile, which is of some soft metal, as lead, and is small enough to be loaded at the muzzle, being made to expand into and take the grooves by the explosion of the powder. The projectile, then, generally has a hollow at the base, in which a wooden or iron plug is inserted. This having less specific gravity than the lead, is driven forward by the discharge, and expands the bullet. It is found also, that when the projectile is proportionately rather long, the hollowed base, either with or without a plug, is unnecessary; the expansion takes place sufficiently without it, from the explosion acting in the manner of a blow, and forcing the base of the cylinder forward before the front has had motion communicated to it. This plan, though very generally adopted for small-arms, has never succeeded with ordnance. In small-arms it is very generally

* Sir W. Armstrong has, however, made some of his large guns muzzleloaders, on the shunt principle, which is of the nature of a mechanical fit.

termed the Minié rifle, Captain Minié, of the French army, having, though he was not the inventor, first brought it very prominently forward. Captain Norton was, we believe, the real inventor of the expanding bullet.

Considering the Armstrong and Whitworth rifles as the most elaborate English types of the two systems of rifling, we will, as far as possible, describe them. In Plate VII. will be seen a drawing of the Armstrong gun, of the shell, and the two fuzes, and drawings of the ordinary and flat-headed Whitworth shot. The process of manufacture of the Armstrong gun is so very complicated that it would be impossible without numerous plates to give a description of any value. Suffice it to say, that the guns are made of wrought-iron bars, coiled and then welded together in lengths of about two or three feet. These tubes are then welded together and formed into a long barrel. This constitutes a core, which is strengthened at the breech, where the action of the powder is the greatest, by similarly made cylinders or tubes of wrought iron, which being constructed of such a size that they are too small when cold, are put on when expanded by heating. When these cool and contract, they afford the necessary initial tension. The breech is forged solid, and welded on. The gun is loaded at the breech through the powerful hollow screw, which is shown in the plate. The charge having been inserted, the vent-piece is dropped into the slot behind it, and tightened up by means of the screw through which the charge was inserted. The vent-piece has a disc of copper on its face, which, by this operation, enters the bore, and by its expansion at the time of explosion prevents any escape of gas. Through the vent in it, the gun is fired. The number of grooves varies in different calibres; in some of the larger ones there being as many as forty. These grooves are very shallow, with one side (the one on which the shot bears while coming out) rectangular, and the other rounded off. The rapidity of twist or pitch of rifling varies from one turn in thirty to one turn in thirty-eight diameters. The bore of the gun, up to a sufficient distance in front of the vent-piece, is smooth and enlarged to form a chamber, into which the shot and charge is pushed by hand.

The following description was given by Sir W. Armstrong, of the projectile-the shell,-in a paper printed by the Institution of Civil Engineers; and with some further description is extracted from Major Owen and Captain Dames's lectures :—

The projectile consists of a very thin cast-iron shell, the interior of which is composed of forty-two segment-shaped pieces of cast-iron, built up in layers around a cylindrical cavity in the centre, which contains the bursting charge and the concussion arrangement. The exterior of the shell is thinly