210 



Article VII. 



On the Deviation of Projectiles ; and on a remarkable Fhceno- 

 menon of Rotating Bodies, By G. Magnus. 



[From the Memoirs of the Royal Academy, Berlin, 1852.] 



I. On the Deviation of Spherical Projectiles. 



It is now a well-known experimental fact, that in firing a ball 

 whose centre of gravity does not coincide with its geometrical 

 centre, a deviation takes place ; and it has been observed, that 

 when the centre of gravity in the gun-barrel is on the right side, 

 the deviation is also to the right ; and similarly, when it is on the 

 left side, a deviation to the left occurs ; when it is above the axis, 

 the range is longer ; when below, shorter. This deviation some- 

 times becomes a very material one, and can be made to amount 

 to one-sixth or even to one-fourth of the whole range, therefore to 

 several hundred yards. The artillery have learnt to provide for 

 this deviation ; and now that attention is paid to the position of 

 the centre of gravity when loading, it has become possible to 

 strike an object with far greater certainty than before. 



An explanation of this deviation has however not yet been 

 given. It has been observed merely, that in shooting with these 

 excentric balls through targets placed at small distances from 

 the cannon, the lateral deviation increases in a greater ratio than 

 the distance. This deviation, therefore, cannot be produced by 

 a force which acted only during the motion of the projectile in 

 the cannon ; as, for instance, by friction against the interior sur- 

 face, or by impinging against this or the outer edge of the can- 

 non ; on the contrary, the deviating force must have been active 

 during the whole time of motion. 



Robins, who first attempted, in his ^ Principles of Gunnery,' 

 to account for this deviation, thought that the deflecting force 

 was generated by the rotation of the projectile ; and at present 

 this opinion is generally accepted. 



