144 OUTLINES OF NAT0EAL PHILOSOPHY. 



The progressive motion, if the moving force and the 

 \bodymoved are given, is determined by the prin- 

 ciples of Dynamics; and the rotatory motion is 

 computed, as if it were about a fixed axis, by the 

 propositions just laid down. 



When one impulse only is communicated to the bo- 

 dy, the axis on which it begins to revolve is a line 

 drawn through its centre of gravity, and perpendi- 

 cular to the plane that passes through that centre, 

 arid the direction of the impulse. 



See Fmsius de Rotatlone clrcum Axem Motum, tlieor. v. 



-*-Opera, torn. it. p. 157. 

 aaol) I^fi.j;iiiji;ii(Vioo sajuq/fli sij k* #oi&dtii> oii 



225. When a body devolves on an axis, and a 

 force is impressed, tending to make it revolve on 

 another, it will revolve on neither, but on a line 

 in the same plane With them, dividing the angle 

 which they contain, so that the sines of the parts 

 are in the inverse ratio of the angular velocities 

 with which the body would have revolved about 

 the said axes, separately. 



This proposition was discovered by FRISI, and is de- 

 monstrated in his works, ubi supra, p. 134. See 

 also the Cosmogra/phfra of the same author, vol. n. 



p. 34. 



' 



If a force be impressed on anybody, by 

 which it is made tfr levolve on "'ah axis, the quan- 

 tity of its momentum, estimated by collecting in- 

 to one sum all the products of the particles into 



their 



