Thermo-electricity and Animal Electricity. 355 



iii. ChemicalDecomposition has not been effected by it. iv. Phy- 

 siological Effects. Nobili has shown* that these* currents are 

 able to cause contractions in the limbs of a frog. v. Spark. 

 The spark has not yet been seen. 



350. Thus only those effects are weak or deficient which 

 depend upon a certain high degree of intensity ; and if com- 

 mon 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 f, 

 Ingenhouszf, Cavendish §, Sir H. Davy ||, and Dr. Davyf, 

 no doubt remains on my mind as to the identity of the electri- 

 city of the torpedo with common and voltaic electricity; and 

 I presume that so little will remain on the minds of others as 

 to justify my refraining from entering at length into the philo- 

 sophical proofs of that identity. The doubts raised by Sir 

 H. Davy have been removed by his brother Dr. Davy ; the 

 results of the latter being the reverse of those of the former. 

 At present the sum of evidence is as follows : — 



352. Tension. — No sensible attractions or repulsions due 

 to tension have been observed. 



353. In motion: i. Evolution of Heat; not yet observed : I 

 have little or no doubt that Harris's electrometer would show- 

 it (287. 359.). 



354. ii. Magnetism. — Perfectly distinct. According to Dr. 

 Davy**, the current deflected the needle and made magnets 

 under the same law, as to direction, which governs currents 

 of ordinary and voltaic electricity. 



355. iii. ChemicalDecomposition. — Also distinct ; and though 

 Dr. Davy used an apparatus of similar construction with that 

 of Dr. Wollaston (327.), still no error in the present case is 

 involved, for the decompositions were polar, and in their na- 

 ture truly electro-chemical. By the direction of the magnet, 

 it was found that the under surface of the fish was negative, 

 and the upper positive ; and in the chemical decompositions, 

 silver and lead were precipitated on the wire connected with 

 the under surface, and not on the other ; and when these wires 

 were either steel or silver, in solution of common salt, gas 

 (hydrogen ?) rose from the negative wire, but none from the 

 positive. 



356. Another reason for the decomposition being electro- 



* Bibliothequc Universcllc, xxxvii. p. 15. + Phil. Trans. 1773, p. 461. 



t Phil. Trans. 1775, p. 1. § Ibid. 1776, p. 196. 



|| Ibid. 1829, p. 15- f Ibid. 1832, p. 259. ** Ibid. 1832, p. 260. 



2 Z2 



