310 On Electrotyping Operations of the U. 8. Coast Survey. 
At this rate, to make a plate one-eighth of an inch thick will 
require forty-five days. So far as I am informed, the above per- 
formance has not been excelled, as to quality and time, on large 
work anywhere prior to its being attained as now to be described. 
The first and most obvious suggestion for increasing the rate 
of deposition is to enlarge the battery; this, however, is incapa- 
ble of producing the desired end. 
To present this subject in a clear and satisfactory manner, I 
will make use of the celebrated formula of Professor Ohm, who 
deduced from mathematical reasoning, and established by experi- 
ment, that the effective force of the current from any battery 
was directly as the electromotive force, and inversely as the re- 
sistance offered to that force. 
‘To express this, he gave the equation — =Q, in which E 
represents the electromotive force, or affinity of acid for zine, 
and Rr the resistance to the current generated by that force; 
R representing the resistance offered to it from the liquid con- 
tained between the positive and negative elements of the battery, 
and r the resistance offered by the object on which the battery 
is working, and Q the amount of work executed, or the quantity 
of the current obtained. 
The resistance of conductors has been found to be directly as 
the length, and inversely as the section. 
o far as concerns form of arrangement, E is constant for the : 
materials used, as it depends on their chemical relations, @ can 
therefore be favorably affected only by varying R or r. Now, as 
R represents the resistance of the liquid contained between the 
battery plates, to increase the size of the plates is only to increase 
the section of the liquid, or, in other words, to diminish the re- 
sistance represented by R. The expression, R fete wynie: 
that, if the resistance in the battery is small compared to the ex- 
ternal resistance, the gain of effect from enlarging the battery 
plates is but small. ; : 
To determine the relative value of R, as compared with 7; * 
tery was constructed so as to collect and measure the ga 
evolved by its action. 
the } were placed in contact with each other, and the 
gas evolved in thirty minutes taken as a unit of effect. Ass 
this case the current did not pass through anything but he 
tery, is no resistance to be represented by r, or rin the za 
mula will be equal to 0 and Q=F=1 
The battery was then attached to a pair of electrodes, ae 
certain solution of sulphate of copper and sulphuric acid, espe 
