ON OHM S LAW. 



47 



Reduction and Comparison of the foregoing Experiments. 



If .B. — In the last set of experiments 52 was used instead of 58 as the bridge correction. 



The first thing to remark is the smallness of the sums of a — ft, 13— y, 

 y — ^) c — e, e— o, as found from single-coil experiments ; the sum is theoreti- 

 cally zero, and the largest deviation is about 20, which divided by 5 gives 

 only 4 for the average error of a determination. Here no error from want 

 of symmetry comes in, and errors from irregular temperature effects very 

 nearly balance each other. 



In the next place, taking the multiple-arc experiments of series Xo. 2, we 

 see that there is a deviation of the observed from the calculated values of 

 a-|(|8 + y-f c + e) which averages 26; and here, from the way the experi- 

 ments were conducted, the temperature disturbances are probably verj^ small. 

 Again, take the multiple-arc experiments of series No. 3. Here, from the' 

 manner of experimenting, the temperature effects will appear. We found that 

 the greatest effect we could produce on one of the coils in a reasonable time 

 was about 15 ; supposing that the whole of this was manifested in the 

 single coil, we shoiild get a quarter as much in each of the coils in the 

 multiple arc (because the current is halved), that is, we have | of 15 alto- 

 gether in a— ^(ft + y+B + e): this necessitates a correction of about 10 to 

 be subtracted from the observed values. This is clearly the maximum 

 correction, for after the first experiiiient we turn into the multiple-arc coils 

 that have ab'eady been fully heated. Supposing, however, that we apply 

 the full correction in each case, we get for the average difference — 1 8. 



This deviation is in the direction indicated by Schuster's experiments, but 



