on 



Galvanometer! 



93 



but, on the whole, even more accurately than the ratio of the 

 resistances to the power §. 



In view, then, of the importance of knowing the self- 

 induction of galvanometer-coils, we give the results of some 

 measurements made by means of the secohmmeter : — 



Reflecting-Galvanometer with One Pair of Coils. 





Resistance, 

 in ohms. 



Self-induction, 

 in secohms. 



Time-Constant, 

 in seconds. 



Front coil 



3007 

 2830 



5837 



3-75 

 316 



9-6 

 1-35 



0-00125 

 000112 



0-00164 



Back coil 



Front and back coils, 1 

 joined up as in actual I 

 use J 



Mutual induction of j 

 the two coils in > 

 position J 



Reflecting-Galvanometer with Variable Damping. 



Four coils in series,! 

 but separated so as 1 

 have little Mutual | 

 Induction J 



9680 



12-48 



0-00129 



Reflecting High-Resistance Galvanometer (fig. 7). 



Top front coil 



105,600 



101,200 



90,000 



207,000 



40-72 

 39-50 

 2751 



109-8 



CO O CO i—l 

 00 050 CO 



co co co o 

 o oo o 

 o o o o 

 o o o o 

 66 6 6 





Bottom front coil 



Front top and back J 

 coils joined up in I 

 position J 



Reflecting Ballistic Galvanometer (fig. 11). 



One Coil only 



1003 



0-166 



0-000166 





Flat Single-Coil Galvanometer. (Nobili type.) 



The one Coil 



64 



0-0324 



0-000506 





From the above it appears that a coil of the ordinary size and 

 shape used in Thomson galvanometers has a coefficient roughly 

 equal, numerically, to one thousandth of its resistance in ohms. 

 If the coils of the instrument are in series and placed near each 

 other, as in actual use, the coefficient is increased by about 

 half its former amount, owing to mutual induction : so that, 



