4 Mr. S. Bidwell. [Feb. 1, 



Table II. — Effect upon Resistance of Increased Electromotive Force. 







Resistance in ohms with 





T> 



X. 1*6 SSIU'C 











G-rms. 













1 cell. 



2 cells. 



cells. 



4 cells 



•25 



11 *10 



7 -20 



4 70 



3 *55 



•5 



5 95 



4 -70 



4-10 



3 50 



1 



4 '40 



3 -65 



3 25 



3 30 



1 '5 



3 "60 



3 20 



2 95 



2 "80 



2 



3 -55 



3 15 



2-80 



2 *50 



2-5 



3 35 



2-95 



2-65 



2-40 



3 



2-90 



2-55 



2 35 



2-30 



3 5 



2-45 



2-30 



2 05 



1-95 



4 



2 25 



2-10 



2-00 



1-90 



4-5 



2-10 



1-95 



1-85 



1-75 



5 



1-95 



1-85 



1-75 



1-70 



7-5 



1-55 



1-55 



1-50 



1 -45 



10 



1 -50 



1-45 



1-40 



1 35 



25 



1 -15 



105 



1-05 



1-05 



It became interesting to ascertain what would be the effect of 

 making still further variations in the strength of the measuring current. 

 A box of resistance coils was therefore inserted between the battery 

 (two Leclanche cells) and the bridge arrangement ; and the weight 

 in the scale-pan remaining the same, various resistances were succes- 

 sively unplugged in the box. Table III gives a few of the measure- 

 ments with pressures of *5, 2*5, 7*5, and 25 grms. This table shows 

 that the resistance of the carbon contacts varies greatly with the 

 strength of the current when the pressure is small, and but very 

 slightly when the pressure is great. 



Table III. 



Added resis- 



Resistance in ohms with pressure of 



tance in 











circuit. 











Ohms. 



*5 grm. 



2*5 grms. 



7' 5 grms. 



25 grms. 







5 6 



2-7 



1-7 



102 



5 





2-8 



1-8 



103 



10 



6-9 



2 -9 



1 -8 



1 -03 



50 



7-7 



3 1 



1 -9 



1 -03 



100 



8-6 



3 1 



1-9 



1 -03 



500 



9 3 



3 1 



1-9 



1-03 



1000 



9 7 



3-1 



1-9 



1-03 



