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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 zinc, each being J^ 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 yf ^ 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. 



