620 
Prof. R. A. Lehfeldt on the Electrochemical 
till balance was obtained. In this way two equations were 
arrived at giving (10 a) X (10 b) and (10 a)~(10 b). 
The final results were 
(10 a) = 9-9986 
(10 b) = 9-9981, 
in terms o£ the ohm as determined at the National Physical 
Laboratory, and it is hardly possible that the error can 
exceed 
1 
20,000* 
3. Time. 
This was determined by a chronometer (Carroll, London, 
No. 505) beating half-seconds. Its rate was not studied 
with care, but was only two or three seconds a day — a 
negligible amount. The duration of the experiments varied 
from 1350 sec. to 4050 sec. There seemed in this the 
possibility of a serious error in timing the make and break 
of circuit by a plug-key, so special experiments were made 
to test it — with somewhat surprising results. The current 
being adjusted beforehand as usual, electrolysis was carried 
on for a period of five or ten seconds, and the mercury 
weighed in the ordinary manner. This gives a value for 
the quantity of electricity flowing that would be affected by 
the error of starting and stopping, and also by the error in 
the initial adjustment of current already spoken of. The 
following short table shows that the two errors combined 
amount to much less than a tenth of a coulomb, i. <?., much 
less than 
10,000 
in the main experiments. 
Time. 
Current. 
Quantity of 
Calculated. 
Electricity. 
Observed. 
seconds. 
5 
amperes. 
0-509 
coulombs. 
2-55 
coulombs. 
254 
7 
0-509 
3-56 
3-53 
5 
0509 
2-55 
254 
10 
0-509 
5-09 
5-12 
• A further possibility of error lies in the adjustment of 
the current; but, as remarked above, the galvanometer 
allowed of detecting a want of balance amounting to ^qqqq, 
and as during a long experiment the current was sometimes 
