AND ON A PHiENOMENON OF ROTATING BODIES. 227 



wind-chest. This was simply a box, 1 foot high, and of equal 

 length and breadth, in which was a four-cornered orifice 3 

 inches square. This large orifice was necessary, in order that 

 the body in every position might remain within the current. 

 As, however, the amount of air furnished by the bellows was 

 not sufficient to sustain a constant and sufficiently strong stream 

 of such a transverse section, a plate was placed before the 

 orifice, containing 484 fine apertures, all equally distant from 

 each other, and all having an equal diameter of 1 millim. 

 Thereby, it is true, not one, but 484, thin parallel currents of 

 air, of equal intensity, were produced, which, however, on 

 account of their close proximity to each other, might be con- 

 sidered as equivalent to one current, at least as far as regards 

 their action on the body L. 



When the apparatus, fig. 6, Plate III., was so placed that the 

 horizontal current of air acted against the body L when this 

 did not rotate, but had its axis situated in the vertical plane 

 through the middle of the current, and at a small inclination 

 towards the horizon, then the apex, if above the horizontal 

 plane through the centre of gravity, was elevated ; but it was 

 depressed when situated below this plane. 



From this, it is evident that the resultant of pressure which 

 the current exercised against the body, passed through the part 

 of the axis between the apex and centre of gravity. 



The action of the air's resistance against an elongated pro- 

 jectile is similar to that of this current against the body. In 

 the former also, when, as in the body L, the centre of gravity 

 is situated in the middle of the length, the resultant of resistance 

 must pass through the part of the axis between the apex and the 

 centre of gravity ; and without doubt this is also the case when 

 the centre of gravity is not at too great a distance from the 

 middle of the axis. 



The elevation of the apex of the body L, and hence that of 

 elongated projectiles also, is dependent alone upon the form of 

 the pointed end; for when the body L was taken out of the 

 rings, and in its pUce a cylinder, with equal diameter and 

 height, substituted, which at each extremity was bounded by a 

 plane perpendicular to its axis; when this cylinder was exposed 

 to the action of the current of air, as the pointed body had been. 



