produced by electricity. 439 
whilst all those of the platinum become intensely and equally 
ignited. This is an important experiment for investigating 
the nature of heat. If heat be supposed a substance, it cannot 
be imagined to be expelled from the platinum ; because an 
unlimited quantity may be generated from the same platinum, 
i. e. as long as the electricity is excited, or as often as it is 
renewed. Or if it be supposed to be identical with, or an 
element of, electricity, it ought to bear some relation to its 
quantity, and might be expected to be the same in every part 
of the chain, or greatest in those parts nearest the battery. 
IX. The magnetism produced by electricity, though with 
the same conductors it increases with the heat, as I mentioned 
in my last paper ; yet with different conductors I find it fol- 
lows a very different law. Thus, when a chain is made 
of different conducting wires, and they are placed in the 
same circuit, they all exhibit equal magnetic powers, and take 
up equal quantities of iron filings. So that the magnetism 
seems directly as the quantity of electricity which they 
transmit. And when in a highly powerful voltaic battery, 
wires of the same diameters and lengths, but of which the 
best conducting is incapable of wholly discharging the bat- 
tery, are made, separately and successively, to form the cir- 
cuit, they take up different quantities of iron filings, in some 
direct proportion to their conducting powers. 
Thus in one experiment, two inches of wire of ~ of an 
inch being used, silver took up 32 grains, copper 24, plati- 
num 11, and iron 8-^. 
