CLARK CELL AS A STANDARD OF ELECTROMOTIVE FORCE. 
579 
one column, passed along it, and after traversing the bridge emerged from the similar 
end of the second column. By sliding the bridge, the length of column traversed by 
the current was varied. A scale of centimetres w 7 as fitted parallel to the grooves, and 
it was found that with a current of about 1 ampere, shifting the bridge by 50 divi¬ 
sions of the scale produced an alteration in the current, which required a change of 
1 ohm in the Box No. 1 to balance it; in other words, the difference of potential 
between the ends of the strip coil was changed by '00025 volt, and the current by 
about '00025 ampere. 
Experiment 4, August 7. 
Values for W 5773, 5775, 5770 ; mean, 5772'5. The difference between the E.M.F. 
of the Clark and Bi was observed, and the resistance out, which was 2149, remained 
unchanged. 
Thus 
W - V = 2149, 
therefore 
V = 3623'5. 
The slide of the rheostat was moved over only about 10 divisions, so that the 
current w r as very constant. Bowls I. and II. used. 
Experiment 5, August 10. 
In this experiment a very large current, about 1'6 ampere, was used. The silver 
was deposited in four bowls, Nos. I. and IV. being arranged in parallel and then in 
series with them, Nos. III. and V. also in parallel. The value of W remained steady 
at 5784, and the value of W — V was also steady. By an oversight the plugs out 
for W — V were not noted till after the experiment w 7 as concluded. They lay 
certainly between 220 and 225, but there is some doubt as to the exact unit; we 
incline to think it w r as 223. With this value we have 
V = 5561. 
The slide was shifted about 24 divisions, so that the variation in the current was 
small. 
Experiment 6, August 12, morning. 
The value of W varied from 5756 to 5754 ; mean W = 5755. The value of 
W — V remained steady at 1176 for 25 minutes, when a sudden change took place. 
The main current was stopped, the time being noted on the chronometer, and the plugs 
altered to 1238. The current was again started, the time being taken, and remained 
fairly steady for 2'5 minutes, when the plugs were altered to 1233 without breaking 
the main current, and the slide correspondingly adjusted. The current remained 
steady for a time, but at the end of 3'25 minutes more showed signs of variation, so 
the experiment was ended and the time taken. 
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