48 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
far thicker than the wires of the galvanometer or of the conducting circuit, and were 
therefore limited in the production of their peculiar action, by those circumstances of 
mass already described (3137.)* To show that that was the case, I now, with the 
thick wire galvanometer, employed two equal loops of copper and iron wire, 0‘2 of 
an inch in thickness, fig. 16 (3133.), passing them equably over the pole of the small 
horseshoe magnet, reduced by the keeper (3134.). The results were very consistent, 
and the mean of them was, for 
o 
Copper 41-7 
Iron 33*7 
3149. Here, therefore, the difference between copper and iron is not so great as 
that of 1 to 1‘24 ; whilst when the conductors, not concerned in the excitement, were 
very good, and able, comparatively, to carry on to the galvanometer nearly all the 
effect of the excitement, it was as great as 1 to 3’5, the difference being in the latter 
case above tenfold what it is in the former. 
3150. To raise the effect dependent upon the mass in relation to that of the con- 
ducting wires to a still higher degree, I had a cylinder of iron, 5*5 inches in length 
and 0 7 of an inch in diameter, soldered on to the ends of conducting wires, so as to 
be in all respect like that of copper before described (3137.). In this case the iron 
not only rose up to the copper in effect, but even surpassed it ; the results being for 
copper 35°’66, and for iron 38°'32. Thus, under these circumstances of mass, the 
difference between iron and copper disappears. The apparent inferiority of copper 
is probably due to the lateral discharge, which before reduced the effect of a cylinder 
below that of a thick wire (3137-). The iron being a worse conductor in itself, and 
having equally good conductors in the prolongation of the circuit as when it was 
employed as wire, would, I think, have proportionately less lateral discharge in it 
than the copper. 
3151. For a comparison, both as regards the particular substance and the mass, I 
attached a similar cylinder of bismuth to conductors. Its effect, with the same 
magnet and force, was 23° ; a very high proportion in relation to the copper, and no 
doubt due to its mass. If it could have been compared as a wire, only 0*04 in dia- 
meter (3145.), it would probably have appeared almost indiflferent (3127.)*. 
3152. So the current of electricity excited in different substances, moving across 
lines of magnetic force, appears to be directly as the conducting power of the sub- 
stance. It appears to have no particular reference to the magnetic character of the 
body, for iron comes between tin and platinum, presenting no other distinction than 
* When bismuth is soldered into the circuit, it requires to be left a long time before it is used for experi- 
ments, and should then be covered up, and the loop handled with great care ; otherwise thermo-currents are 
produced. For an hour or two after soldering it generates electrical currents, which appear at the galvanometer 
very irregularly, being probably due to internal molecular changes, which occur from time to time until the 
whole has acquired a permanent state of equilibrium. 
