e chain of evidence. Water was decomposed by it, and the oxygen and
hydrogen obtained in separate tubes according to the law governing
volta-electric and machine-electric decomposition.

[A] Lond. and Edinb. Phil. Mag. and Journ., 1832, vol. i. p. 161.

[B] Ibid. 1832. vol. i. p. 441.

[C] Annales de Chimie, li, p. 77.

[D] Ibid. li. p. 72

347. iv. _Physiological effects._--A frog was convulsed in the earliest
experiments on these currents (56.). The sensation upon the tongue, and the
flash before the eyes, which I at first obtained only in a feeble degree
(56.), have been since exalted by more powerful apparatus, so as to become
even disagreeable.

348. v. _Spark._--The feeble spark which I first obtained with these
currents (32.), has been varied and strengthened by Signori Nobili and
Antinori, and others, so as to leave no doubt as to its identity with the
common electric spark.

* * * * *

IV. _Thermo-Electricity._

349. With regard to thermo-electricity, (that beautiful form of electricity
discovered by Seebeck,) the very conditions under which it is excited are
such as to give no ground for expecting that it can be raised like common
electricity to any high degree of tension; the effects, therefore, due to
that state are not to be expected. The sum of evidence respecting its
analogy to the electricities already described, is, I believe, as
follows:--_Tension._ The attractions and repulsions due to a certain degree
of tension have not been observed. _In currents_: i. _Evolution of Heat._ I
am not aware that its power of raising temperature has been observed. ii.
_Magnetism._ It was discovered, and is best recognised, by its magnetic
powers. iii. _Chemical decomposition_ has not been effected by it. iv.
_Physiological effects._ Nobili has shown[A] that these currents are able
to cause contractions in the limbs of a frog. v. _Spark._ The spark has not
yet been seen.

[A] Bibliotheque Universelle, xxxvii. 15.

350. Only those effects are weak or deficient which depend upon a certain
high degree of intensity; and if common electricity be reduced in that
quality to a similar degree with the thermo-electricity, it can produce no
effects beyond the latter.

* * * * *

V. _Animal Electricity._

351. After an examination of the experiments of Walsh[A] Ingenhousz[B],
Cavendish[C], Sir H. Davy[D], and Dr. Davy[E], no doubt remains on my