286 



NA TURE 



l/u/y 24, 1884 



to the Government, the objection to his proposals was 

 their extreme novelty, but later on he was told that there 

 was no novelty in the principle of his designs ! 



Mr. Longridge states the problem to be solved in the 

 following satisfactory terms : — 



" Suppose a coil of wire situated near to the inner tube 

 of the gun. It is laid on under a certain tension, but its 

 state is altered by each successive coil which comes over 

 it, and when the gun is completed it is no longer in 

 tension but in compression. 



" There is in a finished gun a certain distance from the 

 centre of the bore at which the wire is in a neutral state ; 

 it is neither in tension nor in compression. All the wires 

 proceeding outwards from this point are in a state of 

 tension varying, according to a definite law, according to 

 the distance from the centre of the gun. All those pro- 

 ceeding inwards are in a state of compression, as is also 

 the inner tube on which they are coiled. 



"In a gun thus constructed the aggregate of all the 

 tensions is exactly equal to that of the compressions 

 whilst the gun is at rest, but when the strain of the explo- 

 sion is brought into action the state of each wire is 

 altered, all the compressions are reduced and eventually 

 changed to tensions, and all the tensions increased : ami, 

 in a gun properly constructed, if the pressure inside were 

 increased to the bursting point, every wire would be 

 strained to its maximum tensile force, and would give way 

 at the same time " (p. 1 5). 



Afterwards Mr. Longridge gives elaborate calculations 

 of the tension proper for each coil of wire. 



The system of "chambering" large guns is now in use 

 at Woolwich, Elswick, and Essen, but it appears most 

 objectionable. We quite agree with Mr. Longridge, that 

 " chambering is a poor and inefficient expedient for 

 lengthening a gun at the cost of its durability." He 

 found "that in the case of the 38-ton 12-inch gun the 

 result of chambering out to 14 inches was to reduce the 

 length of the charge from 27 to 20 inches . . . and that 

 this would ceteris paribus increase the velocity of the shot 

 about 7 or 8 feet per second" (p. 17). In such a case the 

 mere chambering would give an increased longitudinal 

 strain of nearly S20 tons in the chamber, allowing a pres- 

 sure of 20 tons per square inch to the powder gas, while 

 the tendency to burst the coil would be increased in the 

 proportion 6 : 7, or nearly 17 per cent. The Committee 

 on Explosives profess to have discovered a so-called 

 " wave action" which may or may not exist in guns fired 

 under the same conditions. And it is claimed for 

 "chambering" that it (1) gives a higher initial velocity, 

 and (2) prevents the abnormal very high local pressures 

 induced by long cartridges. In the case mentioned by 

 Mr. Longridge 7 inches was the gain in the space through 

 which the powder gas propelled the shot. But the charge 

 being in a more compact form, only 20 inches long, would 

 probably explode more rapidly than it would in the bore 

 27 inches long, and consequently the powder gas pro- 

 pelling the shot at corresponding points in the bore would 

 be greater with the chambering, and consequently in that 

 case the initial velocity of the shot might be expected to 

 be greater, especially with the increment of 7 inches in 

 the useful length of the bore. But it is difficult to imagine 

 in what way chambering could reduce the stress upon the 

 gun. We have found by calculation what would be the 



lengths of the following guns, in o/der to allow the same 

 internal volume : — 



ft. in. 



71-ton Krupp gun, chambered 32 10 long. 



,, ,, unchambered 33 II ,, 



80-ton Woolwich, chambered 26 9 ,, 



,, ,, unchambered 28 1 ,, 



100-ton Armstrong, chambered 32 8 „ 



,, „ unchambered 33 10 ,, 



From this it appears that the saving in total length of 

 gun due to chambering is not great. 



The process seems to have been this. After much 

 trouble guns were manufactured which with a uniform 

 bore and slow-burning powder stood tolerably well. In 

 order to obtain an increased initial velocity the gun was 

 chambered and therefore weakened. Sir W. Armstrong 

 says that the calculated strength of his 100-ton chambered 

 gun, which failed, was " far in excess of what a normal 

 pressure would demand." And then he goes on to state, 

 March 1S80, that " Nothing, in fact, wants investigation 

 so much as this powder question " {Proceedings of the 

 R.A. Institution, Woolwich, vol. xi. p. 197). If chamber- 

 ing is to be profitably used it appears that it will be 

 necessary to adopt steel and abandon coiling— both wire 

 and wrought iron. 



As a uniform bore gives the strongest form of gun, it 

 appears to be very desirable to obtain a slow-burning 

 powder less bulky than that now in use. But if that be 

 not possible, we would either slightly lengthen the gun or 

 use a powder a very little more energetic than that now 

 in use, and just sufficient to compensate for a want of 

 chambering. 



Mr. Longridge quotes the following remark of Messrs. 

 Noble and Abel on air-spacing: — " In cases where there 

 is a considerable air-space between the charge and the 

 projectile, it has been found that the energy developed in 

 the projectile is materially higher than that due to the 

 expansion of the powder gases through the space traversed 

 by the projectile, and the cause of this appears to us 

 clear. 



" When the charge is ignited at one end of the bore, 

 and the ignited products have to travel a considerable 

 distance before striking the projectile, these ignited pro- 

 ducts possess considerable energy, and a portion of this 

 energy will be communicated to the projectile by direct 

 impact" (p. 110). 



Well may Mr. Longridge exclaim : " With all respect 

 to these gentlemen, we are quite unable to accept this 

 explanation." The explanation we have to offer is that 

 when a moderate air-space is left there will be a delay in 

 the initial motion of the shot, and consequently the ex- 

 plosion of the charge for every position of the shot will 

 have proceeded further than if there had been no air- 

 space, and consequently the pressure of the powder gas 

 will on the whole be increased. But, on the other hand, 

 there will be a slight loss of velocity, since the powder 

 gas acts on the projectile through a slightly reduced 

 length of bore corresponding to the air-space. 



We have never made experiments on the pressure and 

 action of fired gunpowder. But we hold that with 

 " chambering " and " air-spacing," using the same powder, 

 the gun must be distressed, if by these means any sensible 

 addition of initial velocity of the shot is obtained. 



Mr. Longridge'appears with reason to recommend the 



