106 Mr Barlow on the Laws of' Electro-Magnetic Action. 
reason for any diminution at all, whatever might be the length 
of the wire ; and, on the other hand', if the diminished action 
were due to such dissipation, then, at that part of the wire near- 
est to the positive pole of the battery, the action ought to be 
much stronger than at the other extremity, where a less quanti- 
ty of the fluid would be returned to the battery than was issued 
at the positive pole. This has reference to the hypothesis of a 
single fluid, agreeably to Franklin’s theory ; but if we admit the 
two fluids issuing from both the extremities of tfte battery, and 
still attribute the diminished action to their dissipation, then at 
least the power exhibited by the centre of the wire ought to be 
much less than that shewn by those parts adjacent to the two 
poles of the battery. My object, therefore, thus became to ex- 
amine, by means of compass needles, distributed at different dis- 
tances along the wire, and with different lengths of the latter, 
the power thus exhibited, and to endeavour to determine the 
mathematical laws of its action, as depending on the length of 
the conducung circuit. 
With this view, I procured about 840 feet of copper-wire, a 
little stouter than that used for bell-wire, and arranged it as 
shewn in Fig. 5. Plate III., where ahcd, a'b'c'd' represent four 
upright props, framed in a square, and their ends driven into 
the ground, the circumference of each frame being exactly 10 
feet. The wire was then brought from P, turned round an up- 
right prop at G, whence it passed to the frame E, about which 
it was revolved in thirty-seven spiral volutions, from the bottom 
upwards, and then passed from b to whence it was made to 
run from the top downwards, in 37 volutions about the frame 
F : it then proceeded from d to H, where it was turned round, 
as at G, to the other extremity N. The whole length of the 
wire was thus 
PG - 154 feet. 
Gc . ~ 144 
374 volutions, frame E, 375 
ba 
374 volutions, frame F, 375 
dn = 144 
NH 154 
Total 838 feet. 
The line ab, a'b\ as also GP, NH, were placed very exactly 
in the magnetic meridian, and Gc and HtZ perpendicular to the 
same, or east and west. The three compasses on which the 
