AND ON A PHENOMENON OF ROTATING BODIES. 225 



move to his left. If the force be applied to the extremity nearest 

 the observer, L e. near to the point b of the base, then the ex- 

 tremity turned from him, or the apex, moves to his left, when 

 the force acts from below upwards ; to his right, however, when 

 it acts from above downwards. If the rotation of the body were 

 in an opposite direction, i. e, contrary to the hands of a clock^ 

 or from right to left, then the extremity of the axis turned from 

 the observer, would in each of the above cases' to<)hrfe*^'fai-*aLri 

 opposite direction to the one mentioned. '"'' ' 



If, instead of the suspended body, an elongated projectile, of 

 the description already named, be imagined, which during its 

 progressive motion rotates around its axis, and the action of the 

 resistance of the air on it be considered, it will be readily seen 

 that the resultant of pressure produced by this resistance passes 

 certainly through the axis, but in general, owing to the presup- 

 posed form of the body, not through its centre of gravity. The 

 resistance of the air, therefore, gives rise to a force which must 

 cause the projectile's point to move laterally, and the axis to 

 describe a cone. Whether this motion of the apex be to the 

 right or left, depends, as we have seen, upon the direction of the 

 resultant of resistance, and whether it acts against the axis above 

 or below the centre of gravity — supposing in both cases the 

 direction of the body's rotation to be the same. 



The above-mentioned observations of projectiles discharged 

 with a small charge of powder, show that the axis has, approxi- 

 mately, the same direction as the tangent ; that, therefore, during 

 the progressive motion, the apex, in reference to the centre of 

 gravity, sinks. It appears to follow from this, that the resultant 

 of resistance passes through the part of the axis under or behind 

 the centre of gravity. Were this the case, however, the apex of 

 a right-rotating projectile would deviate to the left of an observer 

 behind the same; and hence the centre of gravity would be 

 pressed towards this side ; therefore a lateral deviation would 

 be produced exactly contrary in direction to the one actually 

 observed. 



I must confess that this conclusion, contradictory to experi- 

 ment, caused me for some time to seek another explanation of 

 the deviation of elongated projectiles ; until, indeed, the experi- 

 ments which follow showed me that the contradiction was but 



