126 Prof. G. C. "Foster on a Method of Determining 



Ohms. 



, * N Product pr 



r. p (= secondary coil + resistance-box), (absolute units), 



15 194 + 217 6165 xlO 18 



14 +247 6174 



13 +282 6188 



12 +322 6192 



11 +367 6171 



10 +423 6170 



9 +490 6156 



8 +576 6160 



7 +688 6174 



6 +835 6174 



Hence 



Mean value of M/C = 6172-4 x 10 1& 



M = 4-926 x 10- 15 x 6172 x 10 18 = 3-0403 x 10 7 . 

 In these experiments the value of q/r r was about 

 135/(1-65 + ; 6) = m. 

 Hence the greatest sensibility would be with p = Q0r. This 

 condition was nearly fulfilled with 



r = 10 and _p=194 + 423 = 617. 

 In the same way the values of M were obtained for the 

 same pair of coils after displacing the secondary coil endways 

 through various distances. The following are the results 

 obtained : — 



Distance between 

 centres of coils. Value of M. 



centim. 

 0-55 304*0 x 10 5 



1-55 292-4 



2-55 270-5 



3-55 246-4 



4-55 215-9 



5-55 187-8 



6-55 158-4 



7-55 127-2 



8-55 97-3 



9-55 71-1 



10-55 49-7 



11-55 33-0 



12-55 23-3 



13-55 16-5 



14-55 12-35 



15-55 9-48 



These values are represented graphically in the curve (fig. 4), 



