464 RIESS ON THE INCANDESCENCE OF 
occur simultaneously. No incandescence takes place in the wire 
without a bend becoming observable in it, and it is seldom that 
fusion is effected without traces of splitting in the wire. The 
first action in this series is the only one in which heat alone is 
concerned ; if it concurs in the production of any of the follow- 
ing effects, then the calorific and mechanical action must both 
equally be taken into consideration. 
As far as the fusion is concerned, the detailed experiments 
point out so clearly what then takes place, that it will only be 
necessary here to add a very few words. 
We have seen, that by means of increasing discharges, a wire 
is forcibly torn into splinters, which show no trace of fusion, 
that it is then shivered into partially fused splinters, and, lastly, 
is melted into globules. Even in this last case the splintering 
effect is visible from the force with which the globules are scat- 
tered about. Ifa greater mass of metal is only partially melted 
on the surface, the never-failing formation of vapour shows the 
mechanical action which accompanies fusion ; it is not the small 
particles of metal forcibly thrown off that suffer fusion, but these 
enable the remaining portion of metal to melt by loosening and 
lacerating its surface. Wherever electrical fusion takes place a 
mechanical separation of the melted mass is visible; the fusion 
ean therefore only be considered as the effect of heat upon finely- 
divided metal. When fire acts upon a metal, it heats continu- 
ously the whole cohering mass until it melts; electricity, on the 
contrary, only heats a metal to temperatures below the melting- 
point, and fuses it by simultaneous splitting to pieces and heat- 
ing. This then is the essential difference between fusion by fire 
and by electricity, which led Franklin and Berthollet to the 
opinion mentioned in the introduction, according to which elec- 
tricity was supposed to dissolve the cohesion of a metal without 
the aid of heat. That opinion, however, was so far erroneous, 
as no notice was taken of the development of heat which accom- 
panies every electrical discharge long before its mechanical 
powers are exerted, and the facility with which the minute par- 
ticles of metal, when reduced to powder, are oxidized, is clearly 
due to the agency of heat. The mechanism of electrical fusion is 
distinguished from that of ordinary fusion when thus expressed : 
Electricity fuses a metal by simultaneously splitting it in pieces 
and heating it. 
