506 Prof. S. P. Thompson on the Action of 



I. The systems of jointed conductors, dating from the 

 apparatus of Ampere and Faraday, are of innumerable forms, 

 and are generally so well known that there is no need further 

 to specify them. 



II. Systems of Bendable Conductors. — Cumming* devised 

 the elegant experiment of passing a current through a strip of 

 gold-leaf which hung vertically between the horizontal poles 

 of a horse-shoe magnet. The motion of the flexible strip from 

 or towards the magnet served to indicate the direction of the 

 current. A telegraph on this principle was suggested by 

 Highton, and even patented, but never brought into practical 

 operation. 



Le Roux f , in 1860, studied the action of a powerful mag- 

 net upon a long spiral coil of thin platinum wire raised to 

 near its fusing-point by the passage of a current through it. 

 It bent about in a singular manner under the influence of the 

 magnet. 



III. Systems of Conductors of which a Liquid forms a Part. 

 — Davy % was the first to show the rotation of a conducting 

 liquid under the influence of a magnet, employing mercury 

 for that purpose. Later, Poggendorff§ employed the same 

 substance in an important research on the electrodynamic 

 rotation of liquids. 



Liquids which possess electrolytic conductivity were shown 

 by Schweigger || , in 1826, to be capable of exhibiting similar 

 phenomena; and such liquids have been employed in the re- 

 searches of Fechner% Ritchie**, Wartmann ft; Jamin % t, De 

 la Rive § § , Bertin || || , and Plante Tfl. A summary of most of 

 the results of these experimenters is given in Wiedemann's 

 Galvanismus ***. One of Jamin's experiments deserves to be 

 more generally known : if the pole of a powerful electro- 

 magnet be placed between the electrodes of a water volta- 

 meter, it is observed that the bubbles of gas which are being 

 evolved at the two electrodes are whirled off by curvilinear 

 currents of liquid which rotate in opposed senses. 



* 'Electrodynamics.' See also Noad's ' Manual of Electricity/ p. 657 

 (edition of 1859). 



t Annates de Chimie et de Physique, [3 J lxi. 1860, p. 409. 

 \ Phil. Trans. 1823, p. 153. § Fogg. Ann. lxxvii. 1849, p. 1. 



|| Schweigg. Journ. 1826, Bd. xlviii. 5} Ibid. 1829, Bd. lvii. 

 ** Phil. Trans. 1832, ii. p. 294. 

 ft Ann. de Chim. et de Phijs. 1847, [3] xix. p. 394. 

 \X Ibid. 1855, [3] xliii. p. 334. §§ Ibid. 1859, [3] lvi. p. 286. 



HII Ibid. 1860, 1865, and 1869, [4] xvi. p. 74. 



OT BW. Univ. de Geneve, 1860, t. vii. p. 332, and Recherches mr T Elec- 

 tricity pp. 156 and 171, 172. 

 *** Galvanismus, vol. ii. p. 146. 



