The next position assumed for the gun was that of D d, Pig. 1, Plate CCCCXCVII, forming with the principal axis XY, the angle d DV of 27°, this direc tion affording the greatest possible bearing at the stern, towards the opposite quarter of the ship, when the recoil was limited to four feet.' The magnitude of the arc c d, between the extreme bearings at the stern port, was therefore found to be 301° when the rudder-head was preserved, but nearly a degree more when it was removed.
From the foregoing experiments, it therefore ap pears that the entire arc abdba surrounding the square stern, and which amounts in quantity to 204°, may be separated into the Of the defended arcs, it may be observed, that the first arm last a b, a b, admit of a ready defence in any part from either of the after broadside ports; but the second, or right aft portion c c, cannot be defended in every part from the stern ports with the same con venience and security from fire.
For the purpose of affording a more explicit refer ence to the different bearings of the gulls above re ferred to, the following table is added, of which the first column denotes the several angles formed by the lines of fire with the principal axis of the ship; and the second, the distances of the points of intersection formed by the respective lines of fire and the same axis, reckoned from the point K, the centre of the arc surrounding the stern.
Having considered the effects capable of being pro duced by guns applied singly, let us next follow Mr. Harvey into an investigation of their joint action.
Suppose, therefore, in the first place, a square stern vessel to be attacked at the same instant, both on the stern and starboard quarters. It is evident that it would not be possible to fight the after broadside gun directly a-beam, and the adjacent stern gun right aft, at the same time, since the distance between the trains of the carriages, when completely run out, would only amount to fifty inches; and which, when the recoil takes place, would necessarily bring them into contact with each other. One of three things must therefore be done in a case of such a nature; either the former gun must be trained abaft the beam, the fire of the latter be brought nearer to the quarter of the ship attacked, or the latter gun be removed and fought at the other stern port. It might be possible also to
fight both the after broadside guns by training them abaft the beam, with both the stern guns trained right aft; but, as before shown, under no circumstances can the lines of fire be made to cross each other on the quar ters of the ship, a point so 20101 to die desired on so many difficult and trying occasions.
The utmost advantage indeed that can be obtained from crossing the lines of fire, must in strictness be limited to a single combination produced by the stern guns immediately abaft, and confined to the space be tween the lines of extreme fire (Mk, (M•, Fig. 1, Plate CCCCXCVII. It is true, by forming new lines of bearings for the guns, within the limits here re ferred to, all indefinite number of intersecting points may be created; still it is obvious that one only can be obtained at the same time. For example, a point of cross fire may be found at D, produced by the ex treme lines of lire; or by gradually approximating those bearings to each other, other points in the axis XI may be determined, more distant from the stern, thereby commanding the sectorial space D,tr,g. So also, other points may be found, out of the principal axis, by corresponding- bearings of the guns. Thus the points gg may be determined, by combining either of the right aft lines of lire li, li, with one or the ex treme lines of lire dl), di), and sweeping over, by dif ferent modifications of these fines of fire, the secto rial spaces g i k, g i Ir. In like manner, by varying the bearings of the guns, may any, number of points of intersection be determined within the bounds of extreme fire; but only ant, as before remarked, can be determined at the same time. Thus, the advantage of a cross fire, which in military purposes is always of so snuck moment and import«nce, in the case of the square stern, is limited coirfined in an extreme degree.
Front the preceding considerations, it therefore ap pears, that the defence of the square stern is subject to the following disadvantages: First,—Two considerable arcs exist on the quarters, incapable of being defended; and hence a point of im punity is created, from the impossibility of crossing the lines q'fire, which proceed front the after broadside gun, and either of the stern guns.