458 A. Kendrick — Damping of Bell-magnets, etc. 



with box 1 (1st) and inertia moment 1*0, curve III ; and simi- 

 larly with box 3 (or 4#) curves II. and IV respectively for the 

 inertia moments ?y1 and 1*0. [The ordinate of the lower end 

 of curve II, fig. 8, should read *27 instead of *21.] 



F,c 8 



F.c. 9 



r\ 



Majnatie Moment 



Several things appear from these curves. The damping 

 due to these boxes is similar ; it is appreciably less in box 1 

 than in 3 and 4 (a), and almost inappreciably less in 3 than 

 in 4 {a), so the extra thickness of 4$ is superfluous ; when the 

 moment of inertia and magnetic moment are both 1*0, box 1 

 (1st) gives A = O09 and boxes 3 and 4 (a) give A=0-04, the 

 latter practically aperiodic, and the former very satisfactory 

 damping; a comparatively slight increase of the greatest mag 

 netic moment or slight decrease of the least inertia moment 

 would give "dead-beat" vibration; the rate of decrease of A 

 with respect to increase of relative magnetic moment is greater 

 than the rate of decrease of A with respect to decrease of rela- 

 tive inertia moment. 



In what follows Q is used with relative inertia moment and 

 relative magnetic moment each equal to unity. 



The effect of the thickness of the copper in the bottom of 

 these boxes is indicated by fig. 1. Box 1 was used succes- 

 sively with the three thicknesses of bottom shown in fig. 1, and 



