1892.] ly Friction in the Bores of Rifled Guns. 415 



The values of R as given in the last columns of the above tables 

 are graphically shown on p. 414, and from a comparison of the two 

 curves it will be readily seen that, although the maximum pressure 

 between the driving surfaces is not so high with the parabolic as 

 with the uniform rifling, yet, as has been pointed out by Professor 

 Osborne Reynolds, the mean driving pressure is with the parabolic 

 rifling considerably higher, and as the energy absorbed by the friction 

 between the driving surfaces is approximately proportional to the 

 mean driving pressures, the loss of energy with that form of rifling is 

 appreciably greater than with the uniform rifling. 



In the experiments I am now discussing the mean driving pressure 

 throughout the bore was, with the uniform rifling, 7*35 tons ; the 

 mean loss of energy due to the uniform rifling was 21 ft.-tons ; hence 

 he coefficient of the friction between the driving surfaces derived 

 from these particular experiments is /t = 0*199. 



Again, with the ' parabolic rifling, the mean driving pressure 

 throughout the bore is 11*06 tons, and if we had only a similar 

 frict ion to consider, the loss of energy with this rifling should be pro- 

 portioned to the pressure. The loss, however, is much higher, 

 amounting, in fact, to 60 ft.-tons. Part of this extra loss must be 

 ascribed to the continual alteration of form that the copper driving 

 ring is subjected to in its passage up the bore,* but it seems to be 

 doubtful if the whole of this loss can be ascribed to this cause. Part 

 may possibly be ascribed to the ribs being continually forced, so to 

 speak, to ride on to the sloping driving surface ; but the number of 

 rounds in each case being few, a part may possibly be ascribed to 



* The action I refer to will readily be understood from the annexed diagram. 

 If the thick lines represent the plan of one of the grooves at the initial angle of the 

 rifling, the projections on the driving ring will be moulded into that form, and if 

 the light lines represent the groove at its terminal angle it will be seen that the 

 final form of the projections on the ring will be as shown by the shading, while the 

 cross-hatched portion represents the metal removed by the action of the driving 

 surface. 



