1878.] Scale Value of a Thomsons Quadrant Electrometer. 361 



By combining the results of all the above experiments, and taking 

 the means for every hundred cells, we have the following table : 



Positive. 



Negative. 



No. of 



Deflection 



No. of 



Deflection 



No. of 



Deflection 



CeUs. 



in inches. 



Cells. 



in inches. 



Cells. 



in inches. 



100 



93 



600 



3 95 



100 



1-04 



200 



1-77 



700 



4-20 



200 



2 34 



300 



2-48 



800 



4-42 



300 



3 75 



400 



3-09 



900 



4-69 







500 



3 57 











On laying down these values in a curve, making use only of those 

 between the limits of — 200 cells and + 700 cells, as the others are 

 beyond the capability of correct registration by the electrograph, we find 

 a regular smooth curve is produced, which being projected upon one 

 of the ordinates gives a scale by means of which the electrograms are 

 now easily tabulated. 



The value of the electromotive force of one De La Rue chloride of 

 silver cell being 1-03 volt, as determined by Messrs. De La Rue and 

 Miiller (Proc. Roy. Soc, vol. xxvi, p. 324), the scale thus formed 

 has been assumed to represent volts with sufficient accuracy for the 

 required purpose. 



My best thanks are due to Mr. Seaton and Mr. R. W. F. Harrison 

 for assistance rendered me in the prosecution of the experiments. 



