ON OHM S LAW, 



45 



taken at 3.25; the battery was then thrown iu and kept in for about a 

 quarter of an hour with the following results : — 



h m X. 



The reading therefore increased by 15, the greater part of increase taking 

 place in the first 10 minutes. Another series of experiments were made with 

 Biiiglc coils against single, as follows: — 



Time of Ob3. lE.M.C. E.G. 



I I 



L.C. 



4914 

 5137 

 5220 

 6008 



D. 



223 

 218 



These experiments were done as quickly 

 as possible ; the balance, already approxi- 

 mately known, was found by three or four 

 instantaneous contacts, so that the coils 

 were as little heated as possible. 



The battery was thrown in at 12.36 and kept in, the coils being as in last experiment. 



The idea was to get 2 heated and then 

 compare it again with 3, which had been 

 very little if at all heated. 



1.8 ... 

 1.25... 

 1.30... 



5036 

 5036 

 5234 



209 

 198 



Two fresh coils were taken, the middle 

 coils being as before at dilferencc 209. 



Crossed connexions 



4818 



Bridge correction 52. 



Reducing these experiments by the formitla given above svo get 



Several important inferences may be drawn from these experiments, 



1. The difference of resistance between the middle coils decreases as the 

 temperature increases, and that so rcgularlj^, that the value of D may be used 

 as a sort of thermometer, indicating how nearly these coils are kept at the 



' same temperature during any series of experiments. This fact sliows the 

 propriety of using the appropriate value of D for each case in our reducing 

 formula instead of the average value. 



2. The coils 4 and 5 possess the same property, though in a less degree, 



3. The coils 1 and 2 possess this property to a very slight extent. 



4. The greatest effect that could be produced in a reasonable time on the 



