78 
MR. F. E. SMITH ON THE ABSOLUTE MEASUREMENTS OF A 
Table XV.—Mutual Inductances M 2 . 
Distance apart of 
mean planes of 
coils. 
Distance apart of 
contact circles. 
Radius of contact 
circle 2. 
Radius of coils. 
m 2 . 
cm. 
cm. 
cm. 
cm. 
Giving M 2 of Coils on Cylinders Nos. 1 and 2, with the Contact Circle of Disc 2. 
30-20 
167-50 
26-7800 
17-9406 
370-57 
30-50 
167-35 
26-7800 
17-9406 
371-89 
30-50 
167-65 
26-7800 
17-9406 
369-91 
30-50 
167-50 
26-7800 
17-9406 
370-90 
30-55 
167-50 
26-7800 
17-9406 
370-95 
30-60 
167-50 
26-7800 
17-9406 
371-01 
30-80 
167-50 
26-7800 
17-9406 
371-23 
Giving M 2 of Coils on Cylinders Nos. 3 and 4, with the Contact Circle of Disc 1. 
30-20 
167-50 
26-7910 
17-9430 
370-94 
30-50 
167-35 
26-7910 
17-9430 
372-27 
30-50 
167-65 
26-7910 
17-9430 
370-28 
30-50 
167-50 
26-7910 
17-9430 
371-27 
30-55 
167-50 
26-7910 
17-9430 
371-32 
30-60 
167-50 
26-7910 
17-9430 
371-38 
30-70 
167-50 
26-7910 
17-9430 
371-49 
30-80 
167-50 
26-7910 
17-9430 
371-60 
The change in mutual inductance for an increase in radius of any section of the 
coil is most readily calculated by finding clM/clA. for the brush contact circle and a 
second circle of the same radius as the coil, the distance apart of the two circles 
varying over the length of the coil. 
Table XVI. 
d = distance 
apart of the 
circles. 
Radius of first circle = 26’787 cm. 
Radius of second circle = 
Change in M for 
change of 10 /a 
in radius of 
smaller circle. 
cm. 
17-9141 
cm. 
17-9419 
cm. 
17-9697 
M = 
cm. 
23-3150 
88-8782 
- 89-1121 
89-3456 
0-0084 
19-2851 
— 
113-5449 
,113-8412 
0-0107 
15-2573 
— 
145-4984 
145-9000 
0-0145 
11-1679 
— 
187-1127 
187-6662 
0-0199 
7-3135 
232-7922 
233-5633 
234-3348 
0-0278 
