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our senses take cognizance ; that the expression " quantity of 

 electricity" aims at conveying to the mind a condition which 

 cannot be comprehended, and that, therefore, no clear idea of 

 any explanation founded on the notion of " quantity" can be 

 attained. Several considerations, in support of these positions, 

 and an experiment to the same effect, were adduced. In fine, 

 it was concluded, that there is not a known phenomenon the 

 explanation of which receives any real assistance from the 

 assumed agency of quantity. M. Biot, probably perceiving 

 this defect in its alleged operation, has substituted the influence 

 of " velocity." 



Those who sought to establish identity of the different 

 forms of electricity had long been embarrassed by the failure 

 of all efforts to produce deviation of the galvanometer needle 

 by means of common electricity, although it is so easily effected 

 by voltaic. M. Colladon, imagining that this want of success 

 was occasioned by an insufficient quantity or supply of the 

 electric fluid, or by imperfect insulation of the coil of the gal- 

 vanometer, employed one in which particular precautions were 

 taken to insure insulation. With this instrument, placed in the 

 circuit of a very large Ley den battery, a deviation of twenty- 

 three degrees was obtained ; the deviation increased with the 

 intensity of the charge; it sometimes amounted to fortydegrees. 

 When the galvanometer was made part of the circuit between 

 the conductors of a Nairne's electrical machine, the deviation 

 was three or four degrees only ; but when a coil of 500 turns, 

 of the same construction, was substituted, a maximum deflec- 

 tion of thirty-five degrees was produced, provided the cylinder 

 was made to revolve three times in a second. 



Mr. Donovan then stated an experiment of his own in 

 relation to this subject, the object of which was to prove, that 

 in Colladon's experiments it was intensity and not quantity 

 that acted. Other experiments were adduced to prove that, 

 when the electricity is of the voltaic kind, the most feeble in- 

 tensities are far more efficient in causing deflection of the 



