Mutual Induction of a Circle and a Coaxal Helix. 61 



I have performed the calculations for a circle of 5 inches 

 radius situated in the mean plane of a coaxal helix of 10 inches 

 radius and axial length 4 inches. 



In this case, 



A=10, 



a = 5, 



X = 2, 

 c= -942809, 



Q_i=E= 1-113741, 

 Qo =F= 2-528625, 

 Qi = 10-02366, 



Hence 



Qi= 156-6023, 

 Qi= 5419-795 

 Qi = 156574-9 



Q2= 59-23901 

 Q3= 419-7842 

 Q4= 2207-927 



Po= -54870 

 P,= 6-84018 

 P2= 51-4955 

 P3= 391-442 

 P4=1613-68 



M=7z{54-86225 

 -1-69790 

 + -10226 

 - -00823 

 + -00041} 

 =nx 53-25879 



The above investigation was undertaken in connexion with 

 a measurement of a resistance in absolute measure by the 

 method of Lorenz, which I propose making in the Physical 

 Laboratory at Cardiff. The standard coil which I have con- 

 structed for this purpose consists of a helix of copper wire, of 



