LINES OF MAGNETIC FORCE-WIRES OF DIFFERENT THICKNESSES. 
43 
by, and away from, the magnetic axis in one motion, then there was no effect at the 
galvanometer. On the other hand, when the wire was carried across the magnetic 
field as described (3123.), so as to intersect all the lines of force in one movement, 
and sum up their power at the galvanometer, then there was no difference in the 
result, whether the iron cube was in its place or not ; showing, as far as this appa- 
ratus could indicate, that the sum of power in the section of all the lines of force ex- 
ternal to the magnet, was the same under both circumstances, though the distribu- 
tion of it was different. 
3130. The very action produced by the cube, when in and out of place (3129.), 
upon the forces which affected the stationary wire, was a proof of the difference of 
distribution at different times. 
3131. A block of bismuth, employed in place of the iron cube, had no sensible effect 
upon the wire whether it were still or moving. 
3132. This galvanometer was first employed for a repetition of all the former expe- 
riments with the bar magnets (3091. &c.). The results were absolutely the same, 
except that the amount of the deviation produced, when deviation was a result, was 
larger than in the former cases. 
3133. For the comparison of different thicknesses of the same metal, I took copper 
wires in lengths of 10’5 inches, and different diameters, and bending them into loops 
of a form and size such as would admit them to pass with facility over a pole of the 
horseshoe magnet, soldered them to the ends of two conducting rods, made of copper 
wire 0’2 of an inch in diameter and 35 inches in length each, which were fixed on oppo- 
site sides of a narrow slip of wood. The whole Fig- 16. 
arrangement is seen in fig. 16 ; the terminations 
a b dip into the mercurial cups of the galvano- 6 
meter, the parts at c are brought so close together as to touch, except for the in- 
tervention of a piece of card, and thus the parts from do ah are thrown out of 
action, except as mere conductors, whilst the loop, being made to descend over one 
magnetic pole, intersects very nearly the whole of the magnetic curves, and always 
the same proportion. 
3134. The former magnet was too powerful for comparative experiments, therefore 
a smaller one was employed, consisting of five plates, weighing 8 lbs., and able to 
carry 21 lbs. easily at the keeper. The poles were r2 inch apart and an inch thick 
each, in the direction of the magnetic axis. If less magnetic power were required, an 
adjustment was easily made, by applying the keeper to the side upon both limbs, the 
magnetic communication being effected either nearer to the poles, or nearer to the 
equator or bend, as less or more power was required. The descent of the loop be- 
tween the poles is then best regulated by causing the conductor wires to bear ulti- 
mately against a stopping-block. 
G 2 
