420 



Energy absorbed by Friction in Rifled Guns. [Feb. 4, 



Table VIII. Showing the percentage of Loss of Energy due tc 

 Friction in the various Series ; showing also the Deduced Value 

 of the Coefficient of Friction. 



It may be worth while to .1 n tion that, in the groove formerly used 

 in the Service, the angle between the normal to the driving surface 

 and the radius could, without serious error, be taken as = 90. In 

 the groove adopted in the guns under consideration the mean value 

 of 8 is only about 34 45', and this difference in the driving angle 

 ncreases the value of R, and, in consequence, the friction, by about 

 76 per cent. It would be interesting to make careful experiments 

 to ascertain if there be any measurable difference in energy if an 

 angle more nearly approaching to 90 were adopted. On account of 

 the different length of the radius of gyration in the case of a solid 

 shot and of a shell, the value of R is considerably affected when 

 the latter projectile is fired. The difference of values is shown by 

 the curves on p. 414. 



In nearly all the countries of Europe an increasing twist is the 

 form of rifling usually adopted ; and, with such a consensus of prac- 

 tice, it must be assumed that some advantage is supposed to be gained 

 by its use. There is, of course, with the parabolic rifling a less 

 maximum pressure on the driving surfaces ; but, as far as energy is 

 concerned, both theory and the experiments I have detailed concur in 

 showing that there is a distinct and very appreciable loss resulting 

 from its employment. It is quite possible, although I am not 

 acquainted with any carefully-conducted experiments on the point, 

 that superior accuracy may be the advantage obtained ; and if this 

 were decidedly so, a loss of one or two per cent, of energy would not 

 be, perhaps, a serious price to pay ; but as, without any inconvenience, 

 the question of accuracy could be easily settled, I trust that before 

 very long this point also may be definitely determined. 



It only remains to give the results obtained with cordite. At the 

 time the experiments were made, I had only at my disposal a very 

 limited amount of this explosive, and I was only able to fire one 



