[ m ] 
feveral Examples arc given) and the Author makes 
always ufe of it in the Sequel of this Book. 
It is one of the great Advantages of this Method, 
that it fuggefts general Theorems for the Refolution 
of Problems, which may be readily applied as there 
is occafion for them. Our Author proceeds to treat 
of thefc, and firSl of fuch as relate to the Centre of 
Gravity and its Motion. In any SyStem of Bodies, 
the Sum tof their Motions, estimated in a given Di- 
rection, is the fame as if all the Bodies were united 
in their common Centre of Gravity. If the Motion 
of all the Bodies is uniform and redilineal, the 
Centre of Gravity is either quiefeent, or its Motion 
is uniform and redilineal. When Adion is equal to 
Readion, the State of the Centre of Gravity is never 
affeded by the Collifions of the Bodies, or by their 
attrading or repelling each other mutually. It is not, 
however, the Sum of the abfolute Motions of the 
Bodies that is preferved invariable in confequence of 
the Equality of the Adion and Readion, as they feem 
to imagine, who -tell us, that this Sum is unalterable 
by the Collifions of Bodies, and that this follows fo 
evidently from the Equality of Adion and Readion, 
that to endeavour to demonstrate it would ferve only 
to render it more obfeure. On this Occafion the 
Author illustrates an Argument which he had pro- 
pofed in a Piece that obtained the Prize propofed by 
the Royal Academy of Sciences at ‘Paris In 1724. 
againft the Mcnfuration of the Forces of Bodies by 
the Square of the Velocities, Shewing that if this 
Dodrine was admitted, the fame Power or Agent, 
exerting the fame Effort, would produce more Force 
in the fame Body when in a Space carried uniformly 
forwards, 
