IN VOLTAIC ELECTRICITY AND ELECTRO-MAGNETISM. 
293 
before, the needle was equally deflected. The needle is therefore deflected by 
the quantity of electricity conducted, without any regard to the nature of the 
conducting substance. 
Since charcoal therefore deflects the needle, it might be made to rotate about 
a magnet, agreeably to the laws first established by the ingenious experiments 
of Mr. Faraday. This was accomplished as follows : 
Exp. IX. A thin slip of copper, having a small cup soldered on the middle, 
and two short tubes on the ends to hold pieces of charcoal, was placed on the 
point of a needle on the pole of a horse-shoe magnet, the points of charcoal 
being made to dip into the mercury contained in a wooden cup, as in the expe- 
riment for the rotation of a wire. The charcoal was now made to conduct 
voltaic electricity from a battery of a hundred pair of plates, when it revolved 
rapidly, as a metallic wire would have done in similar circumstances. 
21. The French philosophers have introduced a distinction between the cur- 
rent of voltaic electricity passing along a metallic conductor, and that trans- 
mitted by a liquid conductor, which seems to me entirely groundless. This 
distinction may be given in the words of Mr. Cumming in his translation of 
Demonferrand’s Manual of Electro-Dynamics : “ In the present state of 
science it is perhaps expedient to consider electrical currents in another point 
of view, namely, as being continuous or discontinuous. The first are those 
which are transmitted by perfect conductors, and whose intensity varies insen- 
sibly in two consecutive instants ; as in the thermo-electric or in the common 
galvanic circuits. When the conductors are imperfect, the currents are discon- 
tinuous : for bodies of this description permit the electricity to accumulate for 
a certain time, after which, the insulating force being overcome, it passes with 
an explosion ; and if the electro-motive power continues to act, there ensues 
a second accumulation and explosion as before, and so on successively. The 
distinctive character of such currents is, that they are incapable of producing 
a deviation in the magnetic needle 
From the manner in which this distinction is laid down by the French 
writers, I had always taken it for granted that a needle suspended above the 
liquid part of a conductor of voltaic electricity was feebly deflected, and should 
probably have remained in this belief had I not entered on the present ex- 
* Cumming’s Translation of Demonferrand’s Electro-Dynamics, p. 116, 
MDCCCXXXII. 2 Q 
