6 
than with a uniform twist ; and that in the case of grooves 
which develope into parabolas, such as those used in the 
Woolwich guns, the waste from this cause is double what it 
would be if the twist was uniform. I am not aware that 
this fact has ever been noticed. It must not be con- 
founded with the questions already at issue respecting the 
Woolwich or French system of rifling guns. The advocates 
of the gradually increasing twist maintain that it relieves 
the pressure between the studs and the grooves at the breech 
of the gun, where it would otherwise be greatest, while the 
opponents argue that in order to obtain this otherwise 
advantageous result, the bearing surface of the studs has to 
be so much reduced that they are not so well able to with- 
stand the reduced pressure as they are to withstand the full 
pressure with the plane grooves. Now I bring forward a 
collateral point, which has no bearing on the previous ques- 
tion, but which is, in itself, of sufficient importance to 
influence the decision in favour of one or other of these 
systems. I show that apart from any undue wedging or 
shearing of the studs, that with nothing but the legitimate 
friction, the amount of work wasted in imparting rotation 
to the shot is nearly twice as great with the parabolic as 
with the plane grooves. This is important, for, although 
the magnitude of this waste does not appear as yet to have 
been the subject of direct inquiry, it will be seen from what 
follows that with the plane grooves it amounts to more 
than one per cent of the whole energy of the shot, and, con- 
sequently, with the parabolic grooves it will amount to two 
per cent of the energy of the shot ; this is, to say the least, 
important as regards the effect of the discharge ; and when 
we consider that all the work spent in friction is spent in 
destroying the gun and the shot, we see that it becomes a 
matter of the very greatest importance whether the gun 
spends one or two per cent of its power on self-destruction. 
It was established as a fact in the trials of 1863-5, that the 
guns with an increasing twist gave a lower velocity than 
those with the uniform twist. In the trial with the two 
seven-inch guns made especially to test this point, the dif- 
