M. Poiusot on the Percussion of Bodies. 



263 



candle is formed of a glass tube about 8 inches long and |- of 

 an inch in diameter, open below and drawn to a small pointed 



lllllll!lil!lli!liil!:i'ilii'»S 



aperture at top. Some loose cotton-twine or asbestos is intro- 

 duced so as to reach very near to the opening ; the tube is then 

 half-filled with sulphuric aether, and the larger end closed with a 

 cork, after which we may place it vertically in the centre of a 

 wooden block. On applying a light to the apex, the vapour 

 burns in a steady bluish jet, which with proper tubes enables us 

 to repeat all the experiments on the singing and the silent flame. 

 This simple apparatus acts freely at ordinary temperatures, and 

 may be used from time to time for several days without reple- 

 nishing. 



With best regards. 



Yours truly, 



William B. Rogers. 



XXXV. On the Percussion of Bodies. By M. Poinsot. 



[Continued from p. 180.] 



On the points by means of which the body is capable of 

 a given reflexion. 



37. TP we seek the points by means of which the body, on 

 -i- striking an obstacle, may be reflected with a given 

 velocity V, we have merely to make 

 «'=-V. 



Wc thus obtain the quadratic equation 



