1868.] Mr. Longridge on the Resistance of the Air to Projectiles, 263 



wliile my experiments for the same form of head, but with much higher 

 velocities, give 



There is reason to expect that my value of b will require a small reduction 

 for the low velocities used in M. Helie's experiments ; but it is extremely 

 improbable that it can be reduced to M. Helie's value. It will thus appear 

 that M. Helie and I agree in adopting a law of the resistance of the air, 

 but that we have followed quite independent methods in experimenting, and 

 have arrived at different numerical results. 



February 27, 1868. 

 Lieut.-General SABINE^ President^ in the Chair. 

 The following communications were read : — 



I. " On the Resistance of the Air to Rifled Projectiles.^' By J. A. 

 Longridge, C.E. Communicated by C. Manby, Esq, Received 

 February 13, 1868. 



The introduction of elongated rifled projectiles having rendered it neces- 

 sary to reconsider the laws of resistance which had been deduced by Robins, 

 Hutton, and more recent authors, such an investigation is the object of 

 this paper. 



It is first shown that Button's law. 



if applied to the results obtained by the Special Armstrong and Whitworth 

 Committee, 1866, leads to the following equation. 



(Abstract.) 



where Y is the initial velocity, 



V the residual velocity at the distance x from the gun. 

 In like manner it is shown that the law adopted by Piobert, 



leads to the equation 



and the law 



R = A?;HB2;* 



to the equation 



