Again, Sir John Leslie, in his dissertation on the progress of mathematical and physical science, prefixed to the seventh edition of the Encyclopaedia Britannica, Edinb. 1830, p. 622, says, "From a healthy specimen" of the _Silurus electricus,_ meaning rather the _gymnotus_, "exhibited in London, vivid sparks were drawn in a darkened room"; but he does not say he saw them himself, nor state who did see them; nor can I find any account of such a phenomenon; so that the statement is doubtful[A]. [A] Mr. Brayley, who referred me to those statements, and has extensive knowledge of recorded facts, is unacquainted with any further account relating to them. 359. In concluding this summary of the powers of torpedinal electricity, I cannot refrain from pointing out the enormous absolute quantity of electricity which the animal must put in circulation at each effort. It is doubtful whether any common electrical machine has as yet been able to supply electricity sufficient in a reasonable time to cause true electro-chemical decomposition of water (330. 339.), yet the current from the torpedo has done it. The same high proportion is shown by the magnetic effects (296. 371.). These circumstances indicate that the torpedo has power (in the way probably that Cavendish describes,) to continue the evolution for a sensible time, so that its successive discharges rather resemble those of a voltaic arrangement, intermitting in its action, than those of a Leyden apparatus, charged and discharged many times in succession. In reality, however, there is _no philosophical difference_ between these two cases. 360. The _general conclusion_ which must, I think, be drawn from this collection of facts is, that _electricity, whatever may be its source, is identical in its nature_. The phenomena in the five kinds or species quoted, differ, not in their character but only in degree; and in that respect vary in proportion to the variable circumstances of _quantity_ and _intensity_[A] which can at pleasure be made to change in almost any one of the kinds of electricity, as much as it does between one kind and another. [A] The term _quantity_ in electricity is perhaps sufficiently definite as to sense; the term _intensity_ is more difficult to define strictly. I am using the terms in their ordinary and accepted meaning. Table of the experimental Effects common to the Electricities derived from different Sources[A]. Table headings