494 



THE BELL SYSTEM TECHMCAL JOURNAL, MAY 1952 



on the OPQ tnir\'e of Fig. 17 and whose theoretical area W is 



^^, ^ 9(2 -a)fN' ^ 



lOMtt 





1+1- 





../■n. (20) 



where during the oscillation the tangential force T varies between the 

 limits ±T*. Slip takes place as before between the radii a and a' given by 



a' = a A/ I - 



- or conversely — = 1 



(21) 



Since the distribution of traction over the surface cannot be uniquely 

 derived from elastic theory, the introduction of the slip function is an 

 assumption that has to be justified by experiment. This assumption has 

 been shown to correspond with experiment by employing the experi- 

 mental arrangement show^n by the photograph of Fig. 18. A barium 

 titanate driver shown in more detail in Fig. 19 drives the middle of three 

 glass lenses that are pressed together by a static force applied to the 

 lever system as shown by Fig. 19. The central glass lens has a radius of 

 curvature of 4.85 inches on each side while the other two lenses have the 

 same radius of curvature on the sides touching the middle lens, but are 

 flat on the other two sides and are rigidly attached to the lower platform 

 and upper hinged lever by cement. In order to get sufficiently large 



Fig. 18 — BiU'iuiu Uluuale driver, i»ick-ui> device and g)a»6 lenses. 



