RESISTANCE BY A METHOD BASED ON THAT OF LORENZ. 
79 
In Table XVI. we give the values of the mutual inductance of two such circles. 
The radius of one circle is 26787 cm. and the radius of the other circle varies from 
17'9141 cm. to 17"9697 cm. In column 5 of the table we give the change in M for a 
change in radius of the smaller circle of 10/4. 
The values in columns 1 and 5 were plotted and the resulting graph was employed, 
in conjunction with the values of the diameters used in plotting the conicality curves 
(fig. 12), to calculate the correction for the conicality of the coils. The method is so 
obvious that we need only give the results. 
Table XVII.—Corrections to Mi for the Conicality of the Coils. 
Coils on cylinder 
No. 
Correction to Mi. 
Ring end of cylinder 
near disc. 
Ring end of cylinder 
away from disc. 
1 
-0-589 
+ 0-942 
2 
-0-571 
+ 0-494 
3 
+ 0-295 
-0-326 
4 
+ 0-200 
-0-153 
The mutual inductance of one coil and a disc circumference is about 30,000 cm., 
and when cylinder No. 1 is reversed in position a change of 1'5 in M 1} or 5 parts in 
100,000, is brought about by the conicality of the coils. 
Correction for Variation in Pitch. 
The graph of the difference measurements of a coil absolutely uniform in pitch is a 
straight line such as OP, fig. 17. Such a coil may be called a perfect coil and any 
short section of it a “ perfect section.” That there is a difference in the mutual 
inductance of a “ perfect ” section such as OAP and a circle, and an actual section 
such as OBP and the same circle, is easily 
seen. With the exception of the wires 
at O and P, every wire in the actual 2 sju. 
section is farther from the circle than the 
corresponding wires in the perfect section, 
and the mutual inductance of the former 
section will in consequence be the smaller. 
If the periodic curve is symmetrical with respect to the “ perfect ” curve, the reverse 
is true for the next section, but the difference is not so great and hence there is not 
perfect compensation. As we proceed along a coil with such periodic variations the 
( 
- 33 
jVC 
) 
A 
■ 
P 
1 —^ 
3 
Fig. 17. 
