470 



Messrs, Threlfall and Pollock on Measurements 



plate of the resistance arrangement to be put in communica- 

 tion with the last cell so as to charge up without allowing the 



E.J 



LC 



current to rush through the galvanometer. After charging, 

 the connexions were altered so as to allow the current due 

 to the leak through the sulphur to pass through the gal- 

 vanometer. The E.M.F. of the small cells was not changed 

 by this amount of leaking, and the fall of the large cell was 

 measured at the time in the usual manner. The experiment 

 consisted in taking plugs out of the box S till the gal- 

 vanometer gave the same deflexion whether the current was 

 sent through it by the number of cells through the sulphur, 

 or by the adjustable fraction of the E.M.F. of the large cell 

 through a megohm. The sum of the resistances of S and R 

 was always 10,000 legal ohms. The arrangement of the 

 observations was such that they interlocked in time. 



The absolute value of the result, therefore, depends chiefly 

 on the value of the megohm. Respecting this standard I 

 wrote to Messrs. Elliott to inquire what degree of reliance 

 could be placed on it, and was informed in reply that it had 

 been tested against a standard in blocks of 100,000 ohms each, 

 and was right within the variation produced by one degree 

 of temperature. The wire was of German-silver, As the 

 present results are interesting only with respect to the 

 method and the resistances of the sample under varying 

 E.M.F. 's, the absolute value of the megohm is of com- 

 paratively small importance. 



The following table gives the data of the experiments on 

 the resistance of the sulphur : — 



