PRACTICAL STAXDARDS FOR ELECTRICAL MEASUREMENTS. 



149 



This is shown in figs. 1 and 2, in which the observations indicated by- 

 dots give the results of the 1894 experiments, those indicated by crosses 

 the experiments of 1897. At a glance the observations do not appear very- 

 good, but it must be remembered that the vertical ordinates are drawn to 

 a very large scale, the division being tive-milliontlis of an ohm. For both 

 coils the resistance appears to reach a maximum at about 15-.5° C. 



The ten-ohm coils were compared in the usual manner on the Carey- 

 Foster bridge with the Standai-d Coil, Nalder, 371 G. 



The foUowinij are the values found : — 



Nalder, 3873. 



t. 



367. 



The values found in 1893 and 1894 were as follows : — 

 For 3873, 9-9919 at 14-8°. 



If we take the temperature coefficient as -0028 — the value given by 

 Messrs. Nalder — this becomes 9-9894 at 13-9°. Thus the coil appears to 

 have risen in value by -0007 ohms ; 



while for 3874, the value found was 9-9926 at 14-9°. 



Messrs. Nalder give the temperature coefficient as -003, and this leads 

 to the value, 9-9896 at 13-9°, agreeing exactly with the observations of 

 December 1897. 



The results of these observation are shown in figs. 3 and 4. The dots 

 refer to the 1893 observations, the crosses to those of 1897. It appears 

 that No. 3874 has not changed ; with regard to No. 3873, a change is 

 indicated. As to this change, it appears from the note-book that there was 

 some doubt as to the temperature of one of the observations in 1893; it 

 is recorded as 1 4° ; the observation shows that the temperature must have 

 been about 13-7°. Furthermore, the value of the ten-ohm standard used 

 for 3873 was not definitely determined in 1893. If allowance is made 



