356 Miscellanies. 
But another interesting fact is, that when the spark issues from one 
metallic surface and falls upon another, there is a reciprocal transfer 
in opposite currents of each metal to the other. ‘Thus if the spark 
issues from silver and falls upon copper, there is not only a transfer 
of the silver to the copper but also of the copper to the silver. If 
the spark passes from gold to silver, there is a transfer of the silver 
to the gold as of the gold to the silver. 
There are thus produced by the electric current two forcible 
and contrary percussions, occasioned by the metal which has been 
transferred; the one, at the point from which it is detached, the oth- 
er at that where it enters into-the other metal; the existence of these 
two percussions, is shown by the presence of two opposite cavities 
which contain the same metal in a state which proves it to have un- 
dergone.a fusion; hence the metal which passes exerts two pressures 
in contrary directions. 
The electric current in passing from one metal to another, leaves 
the first in the second, and takes a small quantity of the latter. 
The electric spark, which issues from a metal and passes into the 
air, contains a group of molecules, the central portions of which are 
in a state of simple fusion and the exterior portions undergo a com- 
bustion more or less vivid, by their contact with the oxygen, accord- 
~ ing to the greater or less oxydizable nature of the metal. 
The electric sparks between the two poles of a voltaic pile, ter- 
minated either by metals or charcoal, contain also particles of these 
substances, in a state of extreme division and of combustion; the 
ignition of metallic leaves is only an extended scintillation repeated 
from place to place in these leaves, which on account of their ex- 
treme tenuity, may be regarded as discontinuous. 
From the foregoing facts, the author infers ; 
That the electric spark of our machines is not a distinct imponder- 
able fluid as is generally supposed ;—and that the heat and light 
proceed from the ignition and combustion of the particles of ponder- 
able matter.* " 
The author has examined the tracks of the electric current in 
trees, buildings, &c., which have been struck by lightning, and finds 
what he deems to be certain evidences of the transfer of pondera- 
* This reasoning appears to be unphilosophical, inasmuch as ignition always 
presupposes an increase of heat, and therefore to ascribe the heat to ignition, is to 
confound the effect with the cause.— Tr. 
