48 Professor CummtnG on the Developement 
which, I hope, will be both as new, and as interesting, to this 
Society, as they have been to myself. 
My first object was to ascertain whether in this, as in some 
late electro-magnetic experiments, the effect depended on the wire 
being coiled round the bar; but by repeated trials, both on an- 
timony and other metals, it was found to be indifferent, in what 
manner the wire and bar were connected, provided that, in all 
cases, the metallic contacts were complete: I have therefore, 
in general, made the connection, either by soldering, rivetting, 
or casting the bar upon the wire. The result was, that not only 
all the metals, including fluid mercury, but likewise plumbago 
and charcoal, and some, at least, of the metallic sulphurets, 
possess the property of exhibiting electro-magnetism by heat, 
differing, however, both in quantity and quality. If, for instance, 
a bar of bismuth, having copper wires at each end, be heated at 
one extremity; on placing the wires in the mercurial caps of the 
galvanoscope, the heated end produces a deviation on the compass 
needle, in the same direction as a wire from the silver disk, in 
the common galvanic circuit: with antimony it is the reverse. 
(Fig. 1 and 2). These metals may, therefore, so far be considered, 
as positive and negative with respect to each other. 
On examining the other metals with copper wires, I found 
that they might be distinguished into two classes, the heated 
end of the one, and the cooler end of the other exhibiting the 
silver or positive electricity. (Table I). When wires of other 
metals are used, there are modifications, which appear to me 
some of the most singular circumstances in these experiments. 
If the bar be of copper, the deviation becomes negative or posi- 
tive, accordingly as the wires are platina or silver; or if the 
extremities be considered as positive and negative with the one, 
they are negative and positive with the other. The same effect 
was produced with a bar of zine, and zinc or copper wires; and 
