456 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



upon, which, being also plotted upon the chart, Avas, it was 

 evident, the right one. A number of shots were then fired at 

 this turret in order to determine the point of mean impact, 

 and by means of the necessary corrections it was possible to 

 calculate the point of medium impact for the middle of the 

 face of the turret ; and thence by another transfer to compute 

 the elevation and deflection for a point on the sluice just 

 above the water-level in the ditch. A reference to the prac- 

 tice tables showed that at this range a little over one mile 

 about eight or ten per cent, of the projectiles might hit 

 the small sluice-gate at which they were aimed. An exam- 

 ination with a good glass showed, by the showers of Avater, 

 wood, and stone, whether the sluice was hit or not. The 

 bombardment continued w^ith two guns, which were so point- 

 ed that two shots should strike on the face of the sluice about 

 thirteen inches apart. After the fall of Strasburg it was 

 seen that this sluice was very strongly built. Huge cut 

 stones about six feet thick formed the faces of the water 

 sluice-gates. The bombardment had nearly destroyed these 

 gates, and had displaced or destroyed the stone-work, and 

 the water in the ditches had been visibly lowered. Great at- 

 tempts had been made by the French to repair the damages. 

 Minutes of Royal Artillery Institution^ VIIL, 143. 



ROTATION OF RIFLED PROJECTILES. 



In a recent paper by Captain Noble there are given the re- 

 sults of some investigations into the absolute values of press- 

 ures exerted by projectiles, in rifled cannon, against the spiral 

 flange or groove by means of which rotation is given to the 

 shot. This pressure, of course, depends on the angle of the 

 rifling. In certain systems of rifling studs may have scarcely 

 any work to do at the muzzle of the gun, Avhile they may be 

 severely strained at the commencement of the motion ; by 

 which means an unnecessarily severe strain is produced, tend- 

 ing to injure the gun. According to Captain Noble's inves- 

 tigations, guns should be rifled with an increasing twist. If 

 rifled with a uniform twist, it is possible, as in a case quoted 

 by him, that the pressure on the studs may amount to sixty- 

 eisfht tons durino; the first six inches of the shot's movement, 

 but have diminished to nine tons by the time the shot leaves 

 the muzzle; whereas in the case of the accelerated parabolic 



