92 VIBRATIONS CAUSE RECTANGULAR MOTION. 



A similar resultant movement of molecules and 

 bodies at right angles to the surface impinged 

 upon, is illustrated by the parallelogram of forces 

 in the annexed diagram. Elastic particles moving 



obliquely at the angle of 

 incidence, A, impinge 

 upon the surface of B, and 

 rebound at the angle of 

 reflection, c. The result- 

 ant movement will be in the direction D B, at right 

 angles to the surface at the point of impact ; the 

 angle of incidence being equal to the angle of 

 reflection, and in an opposite direction. 



