ON MAGNETISM. 531 



ibid. 1775, p. 395. Ginsan, De Gym. Tubing. 1819. Schonbein, Arch, de 

 1'Electr. i. 445. Faraday, Ph. Tr. 1839, p. 1. Letheby, Proceedings of the Electr. 

 Soc. p. 367. 



Other Animals. Geoffroj ( Anatomy), Bullet, dela Soc. Philom. No. 70 ; Mem. 

 du Musee d'Hist. Nat. i. 392. Rudolphi, Abh. der Akad. Berl. 1820, p. 223. 

 Marianini, Soprala Scossa che provano gli Animali, Venice, 1S28. DuBois, Pogg. 

 Ann. pp. Iviii. 1. Quse apud Veteres exstant Argumenta, Berl. 1843. Nobili, Delia 

 Rana, Mem. i. 135. Matteuci, Arch, de 1'Electr. ii. 628, 419, iii. 5. Essai sur 

 les Phe"n. Electr. des Animaux, Paris, 1840. 



Mineral Electricity. Wilson on the Tourmaline, &c. Ph. Tr. 1759, p. 308 ; 

 1762, p. 443. Due de la Noya Caraffa sur la Tourmeline, 4to, Paris, 1759. Aepinus 

 sur do. Petersb. 1762. Miiller, Au Born. 4to, Vienna, 1773. Bergmann, Ph. Tr. 

 1766, p. 236. Zallinger, Vom Tourm. Vienna, 1779. Haiiy, Hist, et Mem. 1785, 

 p. 206 ; Ann. de Ch. ix. 59 ; Mem. de 1'Inst. i. 49 ; Traite des Characters des 

 Pierres Precieuses, Paris, 1817, p. 146 ; Traite de Mineralogie, 1822, p. 206. 

 Becquerel, Ann. de Ch. xxxvii. 1, 355. Brewster, Ed. Jour. ii. 308. Forbes, Ed. 

 Tr. xiii. 27. Riess and Rose, Pogg. Ann. lix. 553. 



Thermo-Electricity.Seebeck, Abh. der Akad. Berl. 1822 ; Pogg. Ann. vi. 

 pp. 1, 133, 253. Yelin, Der Thermomagnetismus, Munch. 1823. Gumming, 

 Camb. Tr. ii. 1. Becquerel, Ann. de Ch. xxiii. 135, xxxi. 371, xli. 353. Sturgeon, 

 Ph. Mag. 1831, p. 1, 116. Pouillet, Comptes Rendus, v. 785. Prideaux, Ph. 

 Mag. iii. 205, 262, 398. Andrews, ibid. x. 433. Watkins, ibid. xi. 304. Wheat- 

 stone on the Thermo-electric Spark, ibid. x. 414. Matteuci, Bibliot. Univ. xv. 187 ; 

 Arch, de 1'Electr. ii. 227. 



LECTURE LV. 



ON MAGNETISM. 



THE theory of magnetism bears a very strong resemblance to that of 

 electricity, and it must therefore be placed near it in a system of natural 

 philosophy. We have seen the electric fluid not only exerting attractions 

 and repulsions, and causing a peculiar distribution of neighbouring por- 

 tions of a fluid similar to itself, but also excited in one body, and trans- 

 ferred to another, in such a manner as to be perceptible to the senses, or at 

 least to cause sensible effects, in its passage. The attraction and repulsion, 

 and the peculiar distribution of the neighbouring fluid, are found in the 

 phenomena of magnetism ; but we do not perceive that there is ever any 

 actual excitation, or any perceptible transfer of the magnetic fluid from 

 one body to another distinct body ; and it has also this striking peculiarity, 

 that metallic iron is very nearly, if not absolutely, the only substance 

 capable of exhibiting any indications of its presence or activity. 



For explaining the phenomena of magnetism, we suppose the particles of 

 a peculiar fluid to repel each other, and to attract the particles of metallic 

 iron with equal forces, diminishing as the square of the distance increases ; 

 and the particles of such iron must also be imagined to repel each other, in 

 a similar manner. Iron and steel, when soft, are conductors of the mag- 

 netic fluid, and become less and less pervious to it as their hardness in- 

 crea^es. The ground work of this theory is due to Mr. Aepinus,* but the 



* See p. 515. 

 2 M 2 



