1878.] Scale Value of a Thomsons Quadrant Electrometer. 359 



taining a sensitized sheet of paper (such as is used in the self-register- 

 ing photographic instrument at Kew), and having a sliding shutter. 



The image of the illuminated slit reflected from the mirror of the 

 electrometer, falling on this paper made a photographic impression of 

 each deflection of the needle with various numbers of cells in circuit. 

 The time of exposure of the paper was two minutes. 



After the sheets had been developed and fixed the deflections were 

 measured with a tabulating instrument, and the following results 

 obtained. 



Experiment 4, Experiment 5. 



Positive. 



Negative. 



Positive. 



Negative. 



No. of 



Deflection 



No. of 



Deflection 



No. of 



Deflection 



No. of 



Deflection 



Cells. 



in inches. 



Cells. 



in inches. 



Cells. 



in inches. 



CeUs. 



in inches. 







o-ooo 







o-ooo 







o-ooo 







o-ooo 



100 



0-949 



40 



0-410 



100 



0-918 



40 



0-410 



200 



1 -764 



80 



0-880 



200 



1-725 



100 



1135 



300 



2-412 



120 



1 323 



300 



2-406 



160 



1-701 



400 



3-013 



160 



1805 



400 



3 -003 







500 



3-452 







500 



3 454 







600 



3-806 







600 



3-784 







700 



4-049 







700 



4-052 







After these experiments the quadrants were put to earth, and the 

 instrument left until the following morning, when observations were 

 again made of a similar nature. 



It was however observed that the deflections noted were found 

 generally to be somewhat larger than those of the previous day for 

 the same number of cells joined up. 



Experiment 6. 



Positive. 



No. of 



Deflection 



No. of 



Deflection 



Cells. 



in inches. 



Cells. 



in inches. 



100 



0-937 



500 



3-662 



200 



1-837 



600 



4 125 



300 



2 625 



700 



4 337 



400 



3-125 



800 



4 525 



In the next experiment the deflections were measured for every 

 twenty cells added on from 200 negative to 800 positive. 



