392 Sir Humphry Davy on the relations of 
To illustrate the operation of these apparatus, I shall state, 
that when the lower terminating wire, which was to the left, 
or east of the north pole, was connected with a piece of zinc, 
and the upper one with a piece of platinum, both being in 
common water, the deviation of the central needle was eight 
or ten degrees, the south pole turning to the east or left hand ; 
which may be considered as indicating that the current of 
electricity was from the platinum to the zinc through the 
wire, and that the surface of the zinc in the fluid was positive 
with respect to the opposite surface of platinum ; and in using 
the terms positive and negative, I beg to be understood as 
applying them to the metallic surfaces in contact with the 
fluid. 
For determining weak electricities of charge, or as it is 
sometimes called, of tension, I used Volta’s condenser con- 
nected with Bennet’s electrometer, and sometimes with one 
constructed on the principle of Behrens, consisting of an insu- 
lated gold leaf, or what I found better, a silk filament, made 
conducting by impalpable charcoal powder, to receive the 
charge, placed between the poles of a dry pile consisting of 
400 circles of silver and gold foil, of the third of an inch in 
diameter, or 50 of zinc and silver of the same size, with paper 
intervening ; the attraction of the gold leaf or the filament, 
either to the positive or negative pole, indicates the nature of 
the charge : and, as in cases of electro-chemical action there 
are always two corresponding opposite states, I considered 
the part of the system which touched the conductor as pos- 
sessing the same electrical state with that exhibited by the 
leaf. I have never however put much dependence upon 
indications given by this instrument, unless they were con- 
firmed by other results ; having found them very uncer- 
