NATURAL PHILOSOPHY. 183 



the part of the Prussian Artillery Commission, in which Prof. Magnus 

 assisted. The missiles were fired with low charges, so as to allow 

 the motion to be accurately observed, and it was found that the axis 

 remained sensibly in the direction of the tangent to the curved path, while 

 the deviation to the right wa- always clearly marked. He observes that 

 left-handed rifles have never been tried. Prof. Magnus, after some fruit- 

 less conjectures as to the cause, at length sought it in the principle of 

 the composition of rotatory motion. He tried experimentally the effect <of 

 a current of air on a projectile of the form employed, by inserting such a 

 body instead of the rotating sphere in Bonenberger's apparatus, and 

 observing the effect on it, first at rest, and then in rotation, when the 

 strong current of a blowing machine was directed against the conical apex. 

 When at rest, the current elevated the apex, owing to the form of the 

 missile, the resistance acting not through the centre of gravity, but above 

 it : when in rotation no elevation took place, but a deviation in the direc- 

 tion of the axis, in a direction opposite to that of rotation. To show the 

 application of the principle in this case, he observes that the axis of the 

 elongated projectile, which for an instant coincides with the tangent to its 

 curved path, momentarily changes its direction, so that the front extremity 

 or apex falls below its former position. Or, for a single instant, it may be 

 regarded as if locally at rest, but turning about its centre of gravity so as 

 to depress the apex. If the motion were simply in the direction of the 

 axis, the resistance of the air would operate directly against it ; but when 

 the apex is continually tending to turn downwards from that line, the 

 resistance acts against it partially iipwards, and thus tends to raise the 

 apex. Thus, at a given instant, the elongated projectile may be represented 

 by the rotating part of the apparatus just described. When there is no 

 rotation, the resistance of the air tending to raise the apex is represented 

 by the weight at the lower end, which produces the same effect. When a 

 rapid rotation is communicated, (suppose from left to right of the gunner,") 

 the result will be, no elevation of the apex, but a lateral movement, or 

 commencement of a rotation round the vertical, in astronomical lan- 

 guage retrograde, if the former rotation be direct, but which, beginning 

 from the opposite part of the circle, is, relative to the operator, towards 

 the right. The form of the projectile used in these experiments differs 

 from that in the Minie rifle, in that the latter is hollow at its broader end, 

 and thus the centre of gravity is thrown forward towards the apex. 

 Hence, according to the same theory, the effect would probably here be to 

 depress the apex, and therefore to give an opposite deviation : but it does 

 not appear whether any such observations have been made ; and in prac- 

 tice the effect would probably be quite insensible. It occurred to the 

 author that a very simple illustration of this deviation of rifle projectiles 

 might be made by merely forming a sort of small arrow, whose head was 

 composed of a cork, like a shuttle-cock, but, instead of the feathers, small 

 card vanes inclined in the same direction round it, with a tail to balance it, 

 and which thus, in the mere act of tin-owing, acquires a rotatory motion 



