Faraday as a Discoverer HTML version

Chapter 5
Identity of electricities; first researches on electro-chemistry.
I have already once used the word 'discomfort' in reference to the occasional state of
Faraday's mind when experimenting. It was to him a discomfort to reason upon data
which admitted of doubt. He hated what he called 'doubtful knowledge,' and ever tended
either to transfer it into the region of undoubtful knowledge, or of certain and definite
ignorance. Pretence of all kinds, whether in life or in philosophy, was hateful to him. He
wished to know the reality of our nescience as well as of our science. 'Be one thing or the
other,' he seemed to say to an unproved hypothesis; 'come out as a solid truth, or
disappear as a convicted lie.' After making the great discovery which I have attempted to
describe, a doubt seemed to beset him as regards the identity of electricities. 'Is it right,'
he seemed to ask, 'to call this agency which I have discovered electricity at all? Are there
perfectly conclusive grounds for believing that the electricity of the machine, the pile, the
gymnotus and torpedo, magneto-electricity and thermo-electricity, are merely different
manifestations of one and the same agent?' To answer this question to his own
satisfaction he formally reviewed the knowledge of that day. He added to it new
experiments of his own, and finally decided in favour of the 'Identity of Electricities.' His
paper upon this subject was read before the Royal Society on January 10 and 17, 1833.
After he had proved to his own satisfaction the identity of electricities, he tried to
compare them quantitatively together. The terms quantity and intensity, which Faraday
constantly used, need a word of explanation here. He might charge a single Leyden jar by
twenty turns of his machine, or he might charge a battery of ten jars by the same number
of turns. The quantity in both cases would be sensibly the same, but the intensity of the
single jar would be the greatest, for here the electricity would be less diffused. Faraday
first satisfied himself that the needle of his galvanometer was caused to swing through the
same arc by the same quantity of machine electricity, whether it was condensed in a small
battery or diffused over a large one. Thus the electricity developed by thirty turns of his
machine produced, under very variable conditions of battery surface, the same deflection.
Hence he inferred the possibility of comparing, as regards quantity, electricities which
differ greatly from each other in intensity. His object now is to compare frictional with
voltaic electricity. Moistening bibulous paper with the iodide of potassium--a favourite
test of his--and subjecting it to the action of machine electricity, he decomposed the
iodide, and formed a brown spot where the iodine was liberated. Then he immersed two
wires, one of zinc, the other of platinum, each 1/13th of an inch in diameter, to a depth of
5/8ths of an inch in acidulated water during eight beats of his watch, or 3/20ths of a
second; and found that the needle of his galvanometer swung through the same arc, and
coloured his moistened paper to the same extent, as thirty turns of his large electrical
machine. Twenty-eight turns of the machine produced an effect distinctly less than that
produced by his two wires. Now, the quantity of water decomposed by the wires in this
experiment totally eluded observation; it was immeasurably small; and still that amount