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I think it very advisable that for recording the efficient 
working of various modifications of galvanic batteries, three 
observations should be taken, 
1. The electromotive force or intensity should be observed 
by the coil of 100 feet of fine wire, which, on account of 
its resistance being very considerable, will, as regards a 
single pair of elements, indicate the electromotive force of 
the combination, without regard to the size of the elements, 
unless they be extremely small, or the resistance very great ; 
but if it be required to ascertain the electro-motive force 
of a numerous series, several multiples of the resistance of 
the coil should be added in the circuit. 
2. The dynamic effect, or quantity of the combination, 
should be observed by the weight supported by the 10 feet 
coil. 
3. The battery resistance, that is, the resistance of the 
combination of the electrolyte and porous cells, if any be 
used, should be observed. For this purpose I propose two 
methods, derived from those of Professor Wheatstone, but 
which, I think, will be found somewhat simplified, both as 
regards the apparatus and the manipulation required. 
One method of ascertaining the battery resistance is by 
putting in the scale half the weight supported by the 10 
feet coil (as before), and then adding to the circuit a length 
of wire until the half weight be balanced. It is then 
obvious, according to Ohm's law, that the resistances of 
the circuit have been doubled ; the equivalent of the galva- 
nometer coil (10 feet), and also of the necessary connecting 
wires, being deducted, the remainder will be the equivalent 
of the battery resistance. 
Another method is to divert half the current from the 
moveable coil, by putting an equal resistance by its side, 
and observing the weight balanced, then remove the divert- 
ing coil, and add wire to the circuit until the same weight 
