238 ARTILLERY 



at the end of the boro, is then dropped into a recess, and by the action of the screw 

 pressed tightly into its seat, so as effectually to close the bore. 



1 In order to facilitate the loading, the bullet and cartridge are placed in a tubo, 

 from which they are thrust into the gun by moans of a rammer. 



' The breech-piece contains a vent, with a cavity for receiving a small quantity of 

 powder to ignite the charge ; and as the brooch-piece is prepared for firing while the 

 gun is being loaded, no time is lost in subsequent priming. 



' Several of these breech-pieces accompany the gun, some being arranged to fire by 

 percussion-caps, and others by friction-tubes or port-fires. 



' The bore of the gun is one and three-quarter inches in diameter, and contains 

 eight spiral grooves, having an inclination equal to one turn in twelve feet. These 

 grooves terminate at a distance of fourteen inches from the breech, and the bore then 

 gradually expands in a length of three inches, from one and three-quarters inches to 

 one and seven-eighths inches in diameter. The bullet, in the operation of loading, 

 passes freely through this widened space ; but its diameter being a little in excess 

 of the bore, it lodges in the tapered contraction at the commencement of the grooves. 



' The mode in which the gun is made up of separate parts consists in surrounding the 

 steel centre with twisted cylinders of wrought-iron, made in a similar manner to gun- 

 barrels, and being shrunk upon the steel, they are in that state of initial tension 

 which is necessary to bring their entire strength into operation. 



' The weight of the gun by itself is about 5 cwts. ; but, including the carriage, its 

 weight is nearly identical with that of a light 6 -pounder with its carriage complete. 

 It is probably heavier than necessary, but recoil might be inconveniently increased if 

 the weight were much reduced. 



' Haying now described the gun and its carriage, I shall proceed to speak of the 

 projectile. 



' The resistance which a projectile encounters in passing through the air is mainly 

 dependent upon the area of its cross-section, and the advantage of lengthening a 

 bullet consists in augmenting the weight without increasing this sectional area ; but 

 in order to realise this advantage it is essential that the bullet bo guided endways in 

 its course, and this can only be effected by causing it to rotate rapidly upon its longer 

 axis, which is accomplished by firing it from a rifled bore. 



' This peculiar influence of rotation, in giving persistency of direction to the axis of 

 a projectile, is entirely distinct from that which it also possesses of correcting the ten- 

 dency to aberration arising from irregular form or density; and in order to investi- 

 gate experimentally the nature of this action, I constructed an apparatus by which a 

 cylindrical bullet could be put into extremely rapid rotation, and be then suspended 

 in a manner which left it free to turn in any direction. 



' When thus suspended, the rotating bullet exhibited the same remarkable properties 

 as are possessed by the revolving disc in the recently invented instrument called the 

 ' Gyroscope.' When pressure was applied to either end of the axis, the movement 

 which took place was not in the direction of the pressure, but at right angles to it. 

 Thus a vertical pressure deflected the axis horizontally, while lateral pressure de- 

 flected it vertically. But the important point elicited was this, that the time required 

 to produce these indirect movements became greater as the velocity was increased, 

 and, consequently, that the amount of deflection produced in a given time by a given 

 pressure, diminished as the rotation was accelerated. Now, all disturbing forces 

 which operate upon a projectile during its flight must necessarily be of very short 

 continuance, and can therefore have but little influence in diverting the axis when 

 thus stiffened by rapid rotation. 



1 1 also found that a cylindrical bullet with tapered extremities was moro easily de- 

 flected than one of equal weight with flat or merely rounded ends, because the mean 

 diameter of the bullet, and consequently the mean velocity of rotation, wore thereby 

 diminished. So far, therefore, as accuracy of flight depends upon the rigidity of the 

 axis, it would appear that the nearest practicable approach to a plain cylinder is the 

 most desirable form for a projectile, but there are other considerations which modify 

 this conclusion. 



' It is also to be observed, that since the rigidity of the axis (relatively to the 

 magnitude of the projectile) depends upon the mean velocity of rotation, the inclina- 

 tion of the spiral grooves in a rifled gun should vary inversely with the diameter of 

 the bore. Thus, if one turn in eight feet be assumed as sufficient for a rifled bore of 

 one inch in diameter, one turn in forty-eight feet should be sufficient for a bore of 

 eix inches, provided the same form of projectile be used. 



4 The forms of bullet which I actually tried with the gun wore exceedingly nume- 

 rous, and the materials used for these bullets was in all cases lead hardened by an 

 intermixture of antimony and tin ; and tho weight varied from two to three and a 

 half pounds, 



