104 Hare on the Combustion of Iron. 
other.* ‘'Tencontacts of the same disks of copper and zine 
will be found necessary to produce a sensible divergency in 
the leaves of the Condensing Electrometer. That the phe- 
nomenon arises from the dissimilarity of the metals, is easi- 
ly shown, by repeating the experiment with a zine disk, in 
lieu of a disk of copper. The separation of the homogen- 
eous disks will not be found to produce any contact between 
the leaf and ball. 1 believe no mode has been heretofore 
contrived, by which the electrical excitement resulting from 
the contact of heterogeneous metals, may be detected by an 
Electroscope, without the aid of a condenser. It is proba- 
ble, that the sensibility of this instrument, is dependent on 
that property of electricity, which causes any surcharge of 
it, which may be created in a conducting surface, to seek 
an exit at the most projecting termination, or point, connect- 
ed with the surface. This disposition is no doubt rendered 
greater, by the proximity of the ball, which increases the 
capacity of the gold leaf to receive the surcharge, in the 
same manner, as the uninsulated disk of a condenser influ- 
ences the electrical capacity of the insulated disk, in its 
neighbourhood. It must not be expected, that the phe- 
nomenon above described can be produced in weather 
unfavourable to electricity. Under favourable circumstan- 
ces, I have produced it, by means of a smaller Electrome- 
ter, of which the disks are only 23 inches in diameter. 
The construction, as respects the leaf, and the ball, regu- 
lated by the micrometer screw, remaining the same; the 
cap of the condensing electrometer, and its disks, may be 
substituted for the zine disk. 
On the Combustion of Iron, by a jet of Sulphur in Vapour. 
If a gun barrel be heated red hot, at the but end, and a 
piece of sulphur be thrown into it; on closing the mouth 
with a cork, or blowing into it, a jet of ignited sulphurous 
vapour will proceed from the touch-hole. Exposed to 
*T have seen it strike at nearly double this distance. 
+1 think I have seen an effect from a disk only an inch in diameter, or 
from a zinc disk, having a copper socket to its handle. 
