and Resistance of a Galvanic Circuit. 383 
lution of sulphate of zine) and strong nitric acid, or a properly 
acidulated solution of bichromate of potash instead. 
My method of experimenting was as follows. After prevent- 
ing the conducting wires from affecting the tangent compass, 
and determining the intensity of the current within the shortest 
circuit possible, increasing length of platinum wire was, without 
opening the circuit, introduced into it. The reasons for not 
opening the cireuit after each observation, were: 1, the time re- 
_ quired for every observation after the circuit had been opened ; 
2, within the electro-magnetic machine, a similarly gradual 
change of resistance is effected, by means of the brake; 8, the 
rheochord is just designed, partly, to relieve of that tedious 
practice of opening the circuit every time a new resistance is in- 
troduced, and no objections have been raised, so far, against its 
proper use. 
T'o ealculate the constants of the battery I followed the com- 
mon rule, combining the highest intensity within the shortest 
cireuit, with each and every lower intensity. Let I, and [,, 
be the intensities, E the electro-motive force, R the internal re- 
sistance, and P,, P, the respective length of the platinum wire 
of the rheochord, and we have 
sett; E=Rl,. 
? . ° 
have to state that the figures on the “rheochord” line are centi- 
ed. In case 
tensity. The rest of the table will explain itself, or will be 
explained later. 
electro-motive force, exhibit an iner ounting to 100 per 
cent within the range of the experiments, with the decrease 
€ lower intensity which is to be ed with the direct in- 
tensity, or with the increase of the external resistance. I con- 
f, * 
of Ohm, and its experimental proofs by many of the ablest ob- 
servers, led at first to a severe doubt as to the value of my own 
