337 
On the Source of Ponaer in the Voltaic Pile, 
the sole exception of silver positive with respect to copper. The 
inconsistency of these results with any theory of contact electromo- 
tive force is then strongly insisted on by the author. 
The next division of the paper treats of the order of the metallic 
elements of voltaic circuits when different electrolytes are used. It 
is usual to say, that metals are positive or negative with respect to 
each other in a certain order ; but Davy, and afterwards De la Rive, 
showed that, in certain cases, this order must be inverted. The 
author, by using ten metals and seven different exciting electrolytic 
solutions, shows that in no two solutions is the order the same ; but 
that changes of the most extreme kind occur in exact conformity 
with the changes in chemical action, which the use of the different 
solutions occasions. 
The next division of the paper considers the very numerous cases 
in which voltaic circuits, often such as are able to effect decompo- 
sition, are produced without any metallic contact, and by virtue of 
chemical action alone ; contrasting them with the numerous cases 
given in the previous series, where contact without chemical action, 
whether it be the contact of metal with metal, or with chemically 
inactive electrolytes, can produce no voltaic current. 
There then follows a consideration of the sufficiency of chemical 
action to account for ail the phenomena of the pile. It is shown 
that chemical action does actually evolve electricity ; that according 
as chemical action diminishes or ceases, so the electrical current di- 
minishes or ceases also ; that where the chemical action changes 
from side to side, the direction of the current likewise changes with 
it ; that where no chemical action occurs, no current is produced, 
but that a current will occur the moment chemical action com- 
mences ; and that when the chemical action which has, or could 
have produced a current is, as it were, reversed or undone, the cur- 
rent is reversed or undone likewise ; that is, it occurs in the oppo- 
site direction, in exact correspondence with the direction taken by 
the transferred anions and cathions. The accordance of the chemi- 
cal theory of excitation with these phenomena, is considered by the 
author as of the strictest kind. 
The phenomena of thermo-electricity are considered by some 
philosophers as affording proofs of the efficacy of mere metallic 
contact in exciting an electric current. The author proceeds, there- 
fore, to examine these phenomena in relation to such an action, and 
arrives at the conclusion, that they in fact disprove the existence of 
such a power. In thermo-electricity the metals have an order which 
is so different from that belonging to them in any electrolyte, that it 
appears impossible to consider their succession, in any case, as due 
to any mutual effect of the metals on each other common to both 
modes of excitation. Thus, in the thermo-circuit, the electric cur- 
rent is, at the hot place, from silver to antimony, and from bismuth 
to silver ; but in a voltaic series, including dilute sulphuric or nitric 
acids, or strong nitric acid, or solution of potash, the electric current 
is from silver to both antimony and bismuth ; whilst if the 
yellow sulphuret of potash be used, it is from both antimony and 
Phil, Mag, S. 3. Vol. 16. No. 103. April 184<0. Z 
