86 Yes ~ Richard Adie on the 
The battery current was sent in the direction AED, when 
the needles of the galvanometer shewed a current in the 
outer arms, moving in the direction CEB. The two short 
bars were then brought into contact at G, and the current 
through AED established. The galvanometer now shewed 
a current moving opposite to the one first obtained, being in 
the direction BEC. The sole cause of this change was the 
alteration in the joints at G, where the resistance to conduc- 
tion turned off from the main current, passing along AED a 
portion of the electricity into the outer arms. These two ex- 
periments were repeated with the wires H and I immersed in 
a sulphate of copper solution ; the battery current through 
AED was furnished by a single pair of plates ; the electricity 
which appeared in the outer arms readily precipitated metal- 
lic copper; the deposit was on the wire at H, when the 
_ space at G was open; and on I, when the space at G was 
closed. ae 
I have seen it objected to thermo-electrical experiments, 
that they often appear to contradict one another. With this 
experiment of the cross before us, we need not be surprised 
at an alteration in the direction of a feeble galvanic or ther- 
mal current, seeing that it may be brought about by a change 
in resistance to conduction in a joint the current has to cross, 
while the chemical, or molecular action which generates the 
current is unaltered. Cases, in illustration of this view, will 
occur to the minds of those who are familiar with the details 
of the subject. In thermo-electricity, couples formed of sil- 
ver and zinc, and of hard-cast antimony and iron, shew a re- 
versal of the current after the temperature passes. a certain 
point. In hydro-electricity, couples formed of two pieces of 
copper, or any other oxidizable metal, give a-reversal of 
the current, as the rate of oxidation predominates on the 
one or the other slip—instances which give us evidence 
of parallelism between the thermo and hydro electrical 
couple. 
In observing the action of the water battery, I gave a 
series of experiments in vol. xxxviii., p. 99, of this Journal. 
A continuation of these led me to the unexpected result, 
that the active oxidation of a piece of metal converted 
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