[A] Phil, Mag. and Annals, 1832, vol. xi. p. 405.

315. ii. Magnetism.—­These currents were discovered by their magnetic power.

346. iii. Chemical decomposition.—­I have made many endeavours to effect chemical decomposition by magneto-electricity, but unavailingly.  In July last I received an anonymous letter (which has since been published[A],) describing a magneto-electric apparatus, by which the decomposition of water was effected.  As the term “guarded points” is used, I suppose the apparatus to have been Wollaston’s (327. &c.), in which case the results did not indicate polar electro-chemical decomposition.  Signor Botto has recently published certain results which he has obtained[B]; but they are, as at present described, inconclusive.  The apparatus he used was apparently that of Dr. Wollaston, which gives only fallacious indications (327. &c.).  As magneto-electricity can produce sparks, it would be able to show the effects proper to this apparatus.  The apparatus of M. Pixii already referred to (343.) has however, in the hands of himself[C] and M. Hachctte[D], given decisive chemical results, so as to complete this link in the 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.