1854.] OF THE ROYAL INSTITUTION. 397 
The form of the projectile used in these experiments differs from 
that in the Minié 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 pro- 
bably 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 practice 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 throwing acquires a rotatory motion from the re- 
action of the air, to the right or left according as the vanes are 
inclined; and on trying this there was always observed a deviation 
in the direction of the axis or point of the missile to the right or left 
accordingly, relative to the experimenter. It is in fact nearly im- 
possible to throw such a body in a direction perfectly in one plane. 
The true deviation is, however, peculiarly liable to be disguised by 
the general resistance of the air on so light a missile, as well as by 
currents, &c. which it is not easy to guard against. 
The well known case of the Boomerang exhibits effects closely 
similar: for it is found that if so projected that its rotation is from 
left to right, its deviation will be in the same direction, and vice versd: 
that is, supposing (as is the usual case) that its plane is inclined 
upwards from the operator :—If it be inclined downwards, the devia- 
tion is in the direction opposi¢e to that of the rotation. 
In the former case the reaction of the air against the flat surface 
of the missile would tend to increase its inclination upwards, in the 
latter downwards, with respect to the operator: and this in each case 
respectively would give the motion stated; as is easily seen on the 
principle, and by means of the apparatus, before described. 
Thus it would follow that this extraordinary instance of savage 
invention, which long ago puzzled inquirers, is simply a case (like 
the last) of ‘‘ the composition of rotatory motion.” 
It should, however, be mentioned that some experimentalists have 
entertained a different view of the cause of deviation in this instance. 
Besides the results above stated, Professor Magnus (in the same 
Memoir) mentions several other highly curious cases produced by 
certain modifications of the apparatus; but all referrible to the same 
principles. 
M. Fessel has also invented an apparatus (since called the Gyro- 
scope) an account of which is given with some remarks by Professor 
Pliicker, and the Editor in Poggendorff’s Annalen (1853, Nos. 9 and 
10), which though apparently invented without any knowledge of 
Bonenberger’s apparatus, is a modification of it, referring to phe- 
nomena of the same kind as those of the equilibrium experiment 
mentioned at first. 
