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



that of Q and a magnetic moment of about T 8 T that of Q. A 

 would be estimated at about 0*35, and from observation it is 

 0*33. In the series of magnets U, Y, W, the magnetic 

 moment is not reduced as rapidly as the inertia moment, and 

 consequently the damping is maintained, the values of A in 

 box 3 being given by 10, 10, 11 swings respectively. X has 

 a magnetic moment about equal to that of W. Its inertia 

 moment is evidently far greater than Ws. It came to rest in 

 box 3 in 25 swings. Though these estimates of probable damp- 

 ing in the cases just cited are extremely rough, they seemed 

 to the writer to confirm the natural assumption that the damp- 

 ing of any one of these bell-magnets under varying conditions 

 would be typical, and the results would be applicable in 

 general. 



Figures 10 and 11 show transverse vertical sections of cop- 

 per boxes for the circular magnets M and N, 10 belongs to a 

 galvanometer of F. Kohlrausch's pattern. The slot, s, is for 

 the suspension wire and fiber, and extends inward from the 

 front face to the same depth as the hole in which the needle 

 swings. 11 (a) is a copper cylinder of the same outside diame- 

 ter as 4-. The suspension hangs through a small hole, s, in the 

 top, 11 (b) is the same but bored through. 12 is similar to 11 

 {a) but smaller. 13 is a vertical section through the center of 

 a spherical copper box, with spherical cavity. The shell is- 

 divided in two by a horizontal plane, d, just above the flange, 

 the upper portion resting on the lower. Here also s and s r 

 are holes for the suspension and support respectively. M is a 

 circular steel mirror 0*8 mm thick. JST is a ring of rectangular 

 cross section 2 mm thick, with plane glass mirror within. The 

 magnetic moment of M was about 12*7 cgs units, and of ~N> 

 17*2 cgs units. The ratio of the moments of inertia of NtoM 

 was estimated at about 3-f-5. The following table gives in 

 number of swings the damping of each needle by each of these 

 boxes (excepting M in 11 (b)). 





Box 10. 



Box 11 (a). 



Box 11 (Z>). 



Box 12. 



Box 13. 



M 



7 



10 



_. 



7 



15 



N 



5 



7 



8 



5 



10 



From this it is readily seen that the damping of this, ring 

 was more rapid than that of the mirror, that the elliptical box 

 is not superior to the smaller circular box, that the boring 

 through of 11 (b) did not render it much inferior to 11 (a). 

 One would suppose that the slot in the upper part of 10 would 

 perceptibly impair its damping effect. Accordingly a box like 

 9 (a) was taken and the bottom wall slit through vertically 

 from front to back. The damping of N" in this is represented 



