TUE 

 LONDON, EDINBURGH axd DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



MARCH 1858. 



XXIT. On the Percussion of Bodies. By M. Poinsot*. 



Chapter I. 



Theory of the centres of percussion, and of spontaneous rotation, as ivell 

 as of other new centres possessing remarkable properties with respect 

 to the motion of bodies. 



I. On the centre of percussion. 



1. T ET us consider a free body of any form wliateVer, and 

 ■Li let us suppose it to receive a sudden impulse in virtue 

 of the action of a single force P, the direction of which passes 

 at an arbitrary distance from its centre of gravity G. From 

 this centre G let fall a perpendi- 

 cular G C upon the direction of 

 the force P. The foot C of this 

 perpendicular, where the impulse 

 P may be supposed to be imme- 

 diately applied, is the point which 

 I shall call the centre of percussion. 



2, The body which has received this impulse being left to 

 itself, if we consider the individual forces with which its several 

 molecules are animated at any period whatever during its motion, 

 we shall find that all these forces are reducible to a single one, 

 identical with the original impulse P which set the body in mo- 

 tion. This conclusion evidently results from the general prin- 

 ciple of the conservation of forces and moments. 



* The researches of Poinsot are too well known to all mathematicians to 

 render necessary any indication of their merits. Mathematicians at this day, 

 too, are so well acquaiiiteil with the current mathematical htcrature of our 

 continental nei};hhours, that for them even an announcement of the jmbli- 

 cation, in lAouville's Journal for September 1H57, of Poiusot's most recent 

 r/iil. May. S. 4. Vol. 15. No. 09. March 1858. M 



