a Rectilinear Electrical Current on itself. 85 
very same process, of polarity preceding conduction, obtains in 
the ordinary galvanic current. 
The form of the terminals P, N was again altered to a ham- 
mer-shape, as in fig. 6; and now electrical contact with the 
copper horseshoe was even more difficult to obtain than before. 
Though for intensity eight pairs of Grove’s battery and a coil 
were used, the current did not pass without amalgamation, and 
also decided pressure being used; then the adhesion became 
strong, amounting to 140° of torsion of the suspending wire. 
A similar result was obtained when the current was passed 
from one of the hammer-shaped poles A (fig. 7) through a 
straight wire B, laid on the torsion-rod and terminating in a 
small trough of mereur y C, connected with the opposite pole of 
the battery. The adhesion and other phenomena were in all 
respects the same as before. 
I think it will not be doubted that these experiments are far 
more delicate tests than Ampére’s floating wire, of the mutual 
action of two portions of one and the same current, and also 
that the first form is free from the ambiguity which ‘the intro- 
duction of a fiuid conductor occasions. At the same time the 
result, with reference to Ampére’s theory, would be more satis- 
factory if the two rectilinear currents whose mutual action is 
examined were independent of one another, and not parts of one 
and the same current ; for the break in the conductor, necessary 
to the mobility of the parts, mtreduces a peculiarity due rather 
to the force required to propagate the current at all, than to the 
reciprocal action of two currents propagated independently. 
It is needless to add that the result of these experiments is 
not fayourable to the cause which I have assigned to the elec- 
trical vibrations ; but I have not the less thought it desirable to 
record the result, though it leaves that experiment, In my opinion, 
more in need of ‘explanation than ever. 
I have not overlooked the probability of the maintaiing power 
of electricity in the rocking-bar being due to instantaneous in- 
duction currents (Faraday’s) excited at the two points of, con- 
tact of the bar and block round which the rocking takes place ; 
but some experiments made on this supposition led to no result. 
I would, before concluding this paper, direct the attention of 
electricians to another of those isolated experiments connected 
with this subject which require confirmation: I mean the pro- 
duction of “ Davy’s cones,” said to occur when two terminals of a 
very powerful battery, coated with sealing-wax and naked only at 
the ends, are introduced, parallel and vertically, through the bot- 
tom of acup filled with mercury, and reach to within a little space 
of the surface of that fluid. On two occasions—once with 500 
or 600 pairs of the Royal Institution battery, and again with 
