y sulphate of soda, common salt, or other saline bodies. But in
Dr. Davy's experiments with the torpedo, _strong_ solutions of salt,
nitrate of silver, and superacetate of lead were used successfully, and
there is no doubt with more success than weaker ones.

357. iv. _Physiological effects._--These are so characteristic, that by
them the peculiar powers of the torpedo and gymnotus are principally
recognised.

358. v. _Spark._--The electric spark has not yet been obtained, or at least
I think not; but perhaps I had better refer to the evidence on this point.
Humboldt, speaking of results obtained by M. Fahlberg, of Sweden, says,
"This philosopher has seen an electric spark, as Walsh and Ingenhousz had
done before him in London, by placing the gymnotus in the air, and
interrupting the conducting chain by two gold leaves pasted upon glass, and
a line distant from each other[A]." I cannot, however, find any record of
such an observation by either Walsh or Ingenhousz, and do not know where to
refer to that by M. Fahlberg. M. Humboldt could not himself perceive any
luminous effect.

[A] Edinburgh Phil. Journal, ii. p. 249.

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
evolutio