148 



EEPORT — 1886. 



Resistance of Coil, jB, 101 



Mean value 

 Temperature coefficient 



•998815 at 14-15°. 

 •000259 per 1° C. 



Mean value 



Temperature coefficient from this series 



•997860 at 1098°. 

 ■000272 per 1° C. 



On plotting these results it becomes clear at once that the straight line 

 joining the means of the two series will not represent the results at all. 



The first series is represented by the upper curve^ 101 (1), the 



second series by the lower curve I^ 101 (2). 



Thus it would seem that between November 1884 and November 1885 

 this coil had lost in resistance about "00015 ohm at a temperature of 

 1.2° C. Again, the two curves are not parallel, so that it would seem at 

 first sight that the temperature coefficient also has altered ; but this infer- 

 ence is hardly justifiable, for the experiments in series (1) cover the time 

 from November 1884 to July 1885, the high temperature observations 

 being made at the later date ; if then during that period the coil was 

 decreasing in resistance the temperature coefficient would necessarily be 

 too low ; moreover we notice that the observations for July 1885 do not 

 lie very far from the curve which represents the results of the second series. 



We infer then that of the two coils of platinum silver made at the 

 same time — two years from the present date — one |^ 100 has not changed 

 since that date, and has a value of 



•998770 legal ohm at 12'28° 

 ■with a temperature coefficient of •000272, while the other has changed by 



