428 
deflection. The charge was transmitted through various me- 
dia, all intended to retard it more or less, and thus to affect the 
galvanometer with various intensities of electricity. In all 
cases the deflection of the needle was the same, no matter what 
the intensity: hence Faraday concluded that his law was proved. 
To invalidate the inferences and proofs thus drawn, Mr. 
Donovan brought forward a number of considerations to show 
that, in all Faraday’s experiments, the intensity of the elec- 
trical discharges employed was the same or commensurate with 
the deflection of the needle; and that it is the intensity of the 
electricity which passes through the galvanometer, and not its 
quantity, that determines the degree of deflection, the highest 
intensities producing the greatest deflection. 
We should be cautious, therefore, Mr. Donovan observed, 
in applying Faraday’s law : and if the law fail, the comparison 
drawn by him between the quantity of electricity produced 
during chemical action, to be immediately noticed, and that 
discharged from an electric machine, cannot be considered as 
proved. The comparison is this: Faraday found that by 
connecting a galvanometer with a wire of platinum and a wire 
of zine, each being =; inch in diameter, and plunging their 
other ends { inch deep in a mixture of four ounces of water 
and one drop of sulphuric acid, during ;3, of a minute, the 
deflection of the galvanometer amounted to exactly the same 
degree as when, in a former experiment, he passed a charge of 
common electricity through the galvanometer, amounting to 
thirty turns of the large plate-machine received in fifteen jars. 
Each turn of the machine afforded 300 or 360 dense sparks. 
Hence, according to the law, Professor Faraday inferred the 
equality of the two ‘‘ absolute quantities” of electricity from 
the equal deflection of the needle in both cases. The double 
purpose of this experiment was still further to support the in- 
ferred identity of voltaic and frictional electricity, and to estab- 
lish the estimate, already alluded to, of the enormous quantity 
of electricity with which matter is naturally associated. 
