MKASrHlXti FOKCKS AND WI'AK I\ SWlTClll XC AlM'AKATrS 485 



AiiolluM- type of wcivr inoa.surenunit has also been employed. As shown 

 l)y Fiji. 12 Ihe motor is a modification of the Western Electric W re- 

 corder, which was oi'i^inally desi,<;ned for cuttiujj; "hill and dale" phono- 

 j>;raph records/ The moviiiii; syst(>m of this recorder consists of two coils 

 (a drive coil and feedback coil) and a stylus, all rij>;idly coupled and 

 coaxial. The dri\(> coil is s(>cui-ed b) Ihe base of a cone shaped vibrating 



Fig. 12 — Low frequency wear measuring device. 



