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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 Leyden battery, a deviation of twenty- 
three degrees was obtained; the deviation increased with the 
__ intensity of the charge; it sometimes amounted to forty degrees. 
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 
a 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 
