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Aet« XIV.—Ow the Laws qf Electro-Magnetic Action^ as de- 
pending on the Length and Dimensions, qf^ the conducting 
Wire, and on the question, Whether Electrical Phenomena are 
due to the transmission qf a single or qf a compound fluid ? 
By Peter Barlow, F. R. S. 
T? HE question or controversy relative to the two hypotheses 
on which electrical phenomena are explained, is well understood ; 
but still there are such decided proofs advanced by the advo- 
cates on either side, in support of their particular doctrines, that 
it can hardly be said, although the balance seems to incline on 
the side of those who maintain for two distinct fluids, that the 
followers of Dr Franklin, who admit only one fluid, are decided- 
ly in error. 
The following experiments, although directed to another in- 
quiry, may perhaps be found to throw some light on this sub- 
ject, and therefore it will not be amiss, before entering upon a 
detail of them, to point out the views which led me to undertake 
them. In a very early stage of electro-magnetic experiments, 
it had been suggested, that an instantaneous telegraph might be 
established by means of conducting wires and compasses. The 
details of this contrivance are so obvious, and the principles on 
which it is founded so well understood, that there was only one 
question which could render the result doubtful, and this was. 
Is there any diminution of effect by lengthening the conducting 
wire ? It had been said that the electric fluid, from a common 
electrical battery, had been transmitted through a wire four 
miles in length, without any sensible diminution of effect, and 
to every appearance instantaneously ; and if this should be found 
to be the case with the galvanic circuit, then no question could 
be entertained of the practicability and utility of the suggestion 
above adverted to. I was, therefore, induced to make the trial, 
but I found such a sensible diminution with only SOO feet of 
wire, as at once to convince me of the impracticability of the 
scheme. It led me, however, to an inquiry as to the cause of 
this diminution, and the laws by which it is governed. This, 
again, drew my attention to the two hypotheses of electrical ac- 
tion adverted to above. For example, if the electric action were 
due to a current of a single fluid passing through the wire, and 
if none of it were dis>sipated in its course, then one could see no 
