3 1 4 Mr, La ND e isr’s Invefligation of 
It is not only obfervable, that the tracks which the varying, 
poles take, in the furface of any revolving body, are fuch that 
its momentum of rotation may continue the fame whilft its 
angular velocity continues the fame ; but it may be obferved, 
that, in any given body, there is only one fuch track which a 
momentary pole can purfue from any given point. 
If the angular velocity and the momentum of rotation of a 
revolving body were to vary according to the computations ad- 
verted to above, it would follow, that a body might acquire an 
increase of force from its own motion, without being any way 
affedted by any other body whatever, as the fame percuffive 
force, applied at the fame diftance from the momentary axis, 
would not always deftroy the rotatory motion of the body, 
which furely cannot poffibly be true. From the principles or 
laws of motion, which I confider as undoubtedly true (and 
which indeed are no other than the common principles of me- 
chanics), I conclude that a revolving body, not affedted by any 
.external impulfe, can no more acquire an increafe in its mo- 
mentum of rotation, than any other body, moving freely, can 
acquire an increafe in its momentum, or quantity of motion, in 
any given diredtion, without being impelled by gravity or fome 
other force. And the truth of this conclufion (which is here- 
inafter proved by other reasoning) may be eafily inferred from 
the property of the lever; feeing that the joint centrifugal 
force of the particles of the revolving body (which is the only 
difturbing force) has no tendency to accelerate or retard their 
motion about the momentary axis, but only to alter the pofi- 
tion of fuch axis, the diredtion in which that force adts being 
always in a plane wherein that axis will be found. 
By the theory explained in this paper, it appears that a pa» 
rallelopipedon may always be conceived of fuch dimenfions, 
a that 
