3 66 Mr. Children’s experiments 
It is unnecessary to enter into a farther detail of these 
experiments ; it will be sufficient to say generally, that when 
wires of several different metals were introduced at once into 
the circuit, the order of their ignition was precisely that of the 
former experiments. In one experiment with copper and 
gold, the copper was decidedly most heated. 
I feel some difficulty in attempting an explanation of the 
preceding phenomena, and offer the following conjecture with 
diffidence. When a perfect communication is established be- 
tween the poles of the battery, the electricity circulates without 
producing any visible effect ; but if it meet with resistance 
in its passage, it manifests itself by chemical action, by the 
evolution of heat, or both. Thus, if a bar of metal be con- 
nected with one pole of the battery, and its extremity im- 
mersed in a basin of mercury connected with the other pole, 
at the instant the surfaces come in contact, heat and light are 
evolved, which cease as soon as the bar, if it be of sufficient 
size, is fairly plunged beneath the surface of the quicksilver. 
If the circuit be completed by two pieces of charcoal, the 
evolution of heat and light is permanent, as long as their 
surfaces remain in contact, because that contact can never be 
so perfect, as to oppose no resistance to the electricity ; 
whereas, in the case of the bar of metal and the mercury, 
it soon becomes complete, and the current is then uninter- 
rupted. Resistance, therefore, appears to occasion the deve- 
lopement of heat, (whatever be the ultimate cause of the 
phenomenon,) and as this must be inversely as the conducting 
power, when any two of the wires connected continuously are 
placed in the circuit, that which is the worst conductor must 
be most heated; and thus platina, having the lowest conduct- 
ing power, is ignited before all the rest ; and silver, which 
