44 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVIII.) 
3135. The effect of a quick and a slow motion was found to be the same as before 
(3104. 3105.). Such velocities as the hand could impart were very effectual, and 
gave results of very considerable uniformity when quick motions were employed. 
3136. Three different loops were compared together, consisting of copper wire, the 
diameters of which were 0*2, OT and 0*05 of an inch, or as 4, 2 and 1 ; their sectional 
areas or masses therefore were as 16, 4 and 1. Ten or twelve observations were made 
with each loop ; the results were near together, and the average for each loop, being 
the extent of the swing declination on one side from zero, is as follows : — 
Copper wire of ^th of an inch in thickness 16°*00 
Copper wire of ^^th of an inch in thickness 44°*40 
Copper wire of ^th of an inch in thickness 57°'37 
Now though the thicker wires produced the largest effect, the results were evidently 
not at all in proportion to the masses of the wires ; the smaller having greatly the 
advantage in that respect. On the other hand, when four of the smaller wires were 
placed side by side, so as to form one loop equal in mass to the second loop, it gave 
the same result as that loop, being of the same power. 
3137- The disproportion of the difference of these three wires is evidently a con- 
sequence of the relative difference of the mere conducting part of the circuit. To 
compare accurately the effect of the lines of force on wires of different diameters 
moving across them, these diameters should continue to, and through the galvano- 
meter (205.), otherwise the thin wire current has an advantage given to it in the 
conducting part, which the thick wire current has not. Hence the reason why a 
thin wire galvanometer, such as that before described (3086.), gives results which 
are alike, for thick or thin wire loops, or for fasciculi of few or many wires. To 
enlarge the comparison, I soldered on to two pairs of conductors, the dimensions of 
those described (3133.), two cylinders of copper, each 5*5 inches long, but one was 
only 0*2 of an inch thick and the other 0*7, or 
twelve times the mass of the first, fig. 17 . They 
were then passed in succession between the poles 
of the magnet, and gave results very nearly alike. 
If there was any difference, the effect was highest with the smallest cylinder ; and 
this may very well be ; for as the magnetic field was not equal in force, but most 
intense in the magnetic axis, so it is evident, that whilst one part of the large cylinder, 
in passing across, was at the axis, other parts were in places of less intense force and 
action, and so a return current may have existed in them, which could not occur to 
the same extent in a cylinder little more than a fourth of the diameter of the former, 
and which, at the same time, had an outlet for the currents equal to its own diameter, 
through the conducting wires. A similar relation of mass occurs in the case where 
the body of the magnet itself, in revolving, does no more than a small radial wire 
within it (3118.). 
Fig. 17. 
