*380 
MINUTES OE PROCEEDINGS OF 
which Mr. Rigg has supposed has been brought about by a similar 
cause. Doubtless, also, the fluid interior of the globe will exercise a 
disturbing influence; and considering that the laws which govern a 
fluid body in rotation under the influence of impressed forces differ in 
the results produced by them in the case of a rigid body, it is possible 
that the axes of rotation of the two are not coincident, but that there 
is a friction between the two surfaces which produces the magnetism of 
the earth, and also may be the cause of the periodic risings and sub¬ 
sidences of the crust of the globe so well known to geologists, because 
thus the two equators would be continually altering their positions 
with regard to each other. The effect of the laws of rotation on the 
solid and fluid portions of the globe is an interesting speculation, 
which cannot, however, be carried into the dark future, seeing that we 
are met with the prediction that our earth is not destined to last for 
ever. The three laws—heat, elasticity, and attraction of gravitation— 
were given to matter in the first three days of creation. The law of 
heat appears to be the only one which is fading away; but the promise 
is, “yet once again I shake the heavens and the earth/'’ which not only 
appears to establish the undulatory theory of heat, but also may ex¬ 
plain the other statement that “ the elements shall melt with fervent 
heat,” or be dissipated by intense incandescence into space, possibly 
again, under the influence of these same laws, to form new worlds, in 
the way La Place has shown the universe to have been made. 
Seeing, therefore, that the laws of rotation exist, not only in theory, 
but in undoubted fact, no explanation of the motion of a rifled pro¬ 
jectile can be considered satisfactory which leaves them out of account. 
If the shot come out of the gun perfectly centred— i.e., rotating 
round its longest axis, and having that axis coincident with the line of 
flight—there will be no tendency either of the axis of rotation or of the 
projectile itself to deflect, so long as the motion is in a straight line, 
because the resistance of the air will act uniformly all round. As soon, 
however, as the trajectory has begun to curve downwards under the 
influence of gravity, the resistance of the air acts more on the under 
side than on the upper, and effects will be produced depending ou the 
resultant direction of the resistance of the air in relation to the centre 
of gravity. If, as in the case of service projectiles, the resultant action 
be through a point of the axis in front of the centre of gravity, the 
shot will commence to gyrate in the same direction as a top, and the 
resistance of the air, acting on the exposed side of the projectile, will 
cause it to be carried bodily from the trajectory in the direction of the 
deflection of the point; but if the resultant act through a point behind 
the centre of gravity, as is supposed to be the case with cylindrical 
shot,* the gyration will be in the same direction as that of the earth, 
with a corresponding deflection of the shot. In both cases the tendency 
is to gyrate round the trajectory. 
The rate of the gyration will depend on two things—viz., the amount 
of original rotation given to the shot, and the amount of force tending to 
# « Proceedings O.S.C.,” 9th May, 1864, Minutes 11,804 and 11,805. 
