224 Mr. F. J. Bramivell [June 13, 



the interior of the bore, and shows the nature of the rifling. To 

 account to yourselves for the appearance jDresented by this diagram, 

 I will ask you to imagine that the bore of the gun had been lined 

 with a paper tube on which the rifling has been drawn, and that then 

 the tube had been removed from the gun and slit by a straight longi- 

 tudinal cut extending from end to end, and opened out flat, and 

 suspended on the wall before you. This would exhibit, as Diagram 3 

 does, the rifling round the tube when developed on to a flat surface. 

 You will observe that the grooves, where they commence at the 

 rear end, are parallel with the bore of the gun, but that they at 

 once begin to depart from this parallelism, the inclination of de- 

 parture gradually increasing to the very muzzle, at which point each 

 groove is a portion of a helix of such an inclination as would make 

 one complete turn round about the barrel, if that barrel were pro- 

 longed for 35 feet beyond the muzzle. It is technically called 1 turn 

 in 35 calibres ; and the calibre being in this instance exactly 1 foot, 

 the inclination is equal, as I have said, to one turn in 35 feet. 

 Assuming, therefore, that the projectile were moving with a velocity 

 of say 1400 feet per second, which is 40 times 35 feet, that projectile 

 would be spinning on its axis at the rate of 40 revolutions in a 

 second. 



This kind of rifling is called the increasing twist. Diagram 4 

 shows rifling of a uniform twist — that is to say, the departure from 

 parallelism is as great at the very commencement of the rifling as at 

 its termination. 



In the gun under consideration, the vent through which the charge 

 is ignited is at 12 inches forward of the rear end of the bore. 



I need hardly tell you that all the materials used in our guns are 

 most carefully tested. These tests are directed to ascertain not only 

 that the metal will support a certain load, carefully and gradually 

 applied to a specimen of a standard size, before rupture ensues, but 

 also to ascertain that the metal is elastic and tough, and competent, 

 therefore, to support shocks. The elasticity is judged of by the 

 extension which a sample under strain will afford with a given load, 

 such extension disappearing on the removal of that load. The tough- 

 ness is judged of by the total extension occurring before rupture, and 

 by the ability to support bending without fracture. I have already 

 said that the steel tube is toughened in oil ; this toughening, which is 

 performed by heating the steel and then cooling it in oil, has a 

 very marked effect in increasing the resistance to strain, and also 

 in increasing the elastic limit. Speaking generally, when the steel 

 is reduced to the size of the test sample before the toughening, a 

 specimen which would require, when untoughened, 30 tons per square 

 inch to break it, will, when toughened, require 45 tons, while the elastic 

 limit, which in the untoughened state would be attained by a strain of 

 about 15 tons per square inch, will in the toughened state not be 

 reached under 30 tons to the square inch. Samples of iron and steel 

 are on the table, and an examination will show how, before rupture, 



