184 



Colonel H. WatJcin 



[May L 



severed. After trying several methods, the following, which has 

 proved most satisfactory, was worked out. A soft steel wire. Fig. 4, 

 A B C, bent as shown in this diagram, has the bent portion B hardened 

 at two points, where it projects from the plug into the gun. The 

 wire is covered with india-rubber tubing to insulate it from the plug, 

 and a plug of asbestos packing D, pressed hard by a screw piston 

 E, prevents any escape of gas. After the first 

 experiment we found the compressed air in front 

 of the projectile pressed the wire away from the 

 breech and altered its position very slightly; 

 so now boxwood ferrules are placed over the wire 

 instead of the rubber tube, for a short distance 

 from the bottom of the plug. The holes in the 

 gun are bored spirally round the gun, so as not 

 to weaken it in one line. The gun we have been 

 experimenting with is really a 7-inch gun, with 

 a bore of 4*7 inch diameter, and 60 calibres long. 

 The great length gives us the opportunity of 

 ascertaining what gain in muzzle velocity is 

 obtained by additional length. Some of the 

 plugs at the breech end where the rise of pres- 

 sure is very rapid, are only 2 inches apart, the 

 distance increasing towards the muzzle where 

 they are 20 inches apart. Here the pressure is 

 comparatively small, but the velocity of the shot 

 is very great. 



The sketch, Fig. 5, shows the arrangement 

 of wires from the different parts of the appa- 

 ratus. Only a few wires are shown to avoid 

 confusion. 



Here the lecturer showed the working of the whole apparatus, 

 firing a pistol to break a series of screens representing the bore of a 

 gun. Eecords were obtained on the drum of the breaking of the 

 screens by the bullet, and the speed of the drum was determined by 

 a drop weight, similar to that shown at Fig. 3. 



The readings obtained on the divided circle are translated into 

 time, and plotted on a very large scale in the Koyal Gun Factory, 

 and the velocity and pressure curves calculated. Here is a specimen 

 of the curve. The working out of a round is a laborious affair, 

 taking about a fortnight. 



Now it may be rightly asked — How do we know that the records 

 on the drum are true ? Are the cutter plugs reliable, and the records 

 given by the induction coil accurate ? To test the question of the 

 cutter plugs, two plugs were placed, one on the top side of a gun, 

 and one on the bottom side, but at exactly the same distances from the 

 muzzle. The circuits for these were entirely distinct. On firing the 

 gun identical records were obtained. Now as regards the records of 

 the sparks, whether they vary, and how long after the rupture of the 



Fig. 4. 



