Whitehead and Hill — Measurement of Self -Inductance. 153 



This method did not prove satisfactory for measuring self- 

 inductance. With care it is possible to obtain values which do 

 not differ among themselves by more than 1 per cent. One 

 drawback to the method is its lack of sensibility, that is, it is 

 not usually possible to adjust the resistances closer than one 

 part in three hundred. Again, since the electrodynamometer 

 was very "dead beat" it required a certain small time to com- 

 pare the deflections, to be sure not long, but enough for the 

 current period to alter slightly unless special precautions were 

 taken. A few determinations of the self -inductance of coils S 

 and C are given. It will be noticed that the values are lower 

 than those obtained later by a more accurate method. This is 

 probably due to the use of ordinary resistance boxes possessing 

 electrostatic capacity. This method was the first tried and is 

 the only one in which such resistances were used. 











Table I, Coil C. 







Zero. Deflection. 



R. 





R'. 



r. 



n. 



L. 



24-98 



15-30 149-7 



1513-7 4-017 57-567 1-266 henrys 



it 



15-49 



a 





1531-7 



" 57-227 1-282 " 



24.82 



15-18 



a 





1518-7 



57 



453 1-2 



71 " 



a 



15*11 



a 





1530-7 



57 



510 1-275 " 



24-77 



12-70 199- 



7 



1241-7 



" 57-453 1-2 



76 " 



24-73 



12-62 



a 





1238-7 



57 



510 1-273 " 

 Mean 1-274 " 









Table II. Coil S. 







Zero. 



Deflection 





r. 



R. 



R' 



n (cycles). 



L (henrys) 



240-0 



158-2 





4-017 1-5 



1300-7 



63-885 



1-023 



a 



158*5 





n 



a 



1283-7 



63-62 



1-021 



a 



it 





a 



a 



12837 



63-329 



1-020 



239-2 



301-0 





a 



a 



1288-7 



63-261 



1-028 



tt 



a 





a 



a 



1281-7 



a 



1-025 



239-0 



134-2 





a 



191-5 



1041-7 



64-095 



1-012 



a 



134-8 





u 



a 



1038-7 



63-955 



1-013 



238-7 



345-8 





a 



a 



1036-7 



a 



1-012 



a 



a 





a 



a 



1038-7 



a 



1-013 



249-0 



121-3 





u 



241-5 



920-7 



64-095 



1-014 



u 



a 





it 



a 



922-7 



a 



1-015 



239-1 



129-9 





a 



291-5 



850-7 



64-167 



1-009 



a 



a 





a 



a 



a 



64-095 



1-010 



239-7 



it 





a 



491-5 



836-7 



6423 



1-025 



Mean 1-0171 henry 



TI. 



Method llf,. — The next method tested was that which in Pro- 

 fessor Rowland's paper is number 14. It is an absolute method 

 for measuring either self-inductance or capacity. It is a zero 



