542 LECTURE LV. 



electric current are attained, and very little ingenuity is requisite to 

 render the machine available as a powerful electrical machine of a peculiar 

 character. 



The last mode of developing a current which we shall mention is that 

 discovered by M. Arago.* If a plate of copper be made to rotate with 

 considerable rapidity in a horizontal plane, a magnetic needle placed above 

 or below it tends to follow its motion, and that quite irrespective of the 

 motion of the air, as may be proved by interposing a plate of glass or 

 other substance between them. It is evident that this effect is due to the 

 evolution of a current of electricity, which travels from the centre to the 

 circumference of the plate. For further information, the reader is referred 

 to Faraday's Researches ; he will also find an excellent article on electro- 

 magnetism, by Roget, in the Library of Useful Knowledge.] 



LECT. LV.-ADDITIONAL AUTHORITIES. 



Treatises. Peregrinus, De Magnete, 4to, Augsb. 1558. Norman, The New 

 Attractive, 4to, 1596. Ridley, On Magn. Bodies and Motions, 4to, Lond. 1613. 

 Cabseus, Philosophia Mag. fol. Ferrara, 1629. Kircher, Magnes, 4to, Col. 1643. 

 Lieutaud. Magnetologia, 4to, Lugd. 1668. Dalance, Traite de 1'Aimant, 4to, Liege, 

 1691. Eberhard's Mag. Theorie, 4to, Leipz. 1720. Becker, Der Mineralische 

 Mag. Miihlh. 1729. Euler, D. and J. Bernoulli, Dutour, Pieces qui ont rem- 

 portees la prix de 1'Acad. 4to, Paris, 1748. Du Fay, Amnerkungen, Erf. 1748. 

 Penrose on Mag. 1753. Adams's Essay, 4to, 1753. Scarella, De Mag. 2 vols. 

 4to, Brescia, 1759. Cooper's Experimental Mag. 1761. Wilcke, Tal om Mag. 

 Stock. 1764. Brugmann, De Materia Magnetica, 4to, Franeker, 1765. Lo- 

 vett's Electr. and Mag. 1766. Van Swinden, De Phsen. Mag. Lugd. 1772. 

 Recueil de Mem. sur 1' Analogic de 1'Electr. et du Mag. 3 vols. Haag. 1784. Le- 

 monnier, Loix du Mag. 2 vols. 1776. Gabler, Theoria Mag. Ingolst. 1781. 

 Cavallo on Mag. 1787. Walker, 1794. Lorimer, 4to, 1795. Haiiy, Expos, de la 

 Theorie, Altenb. 1801. V. Lowerrorn, Ueber den Magnet. Kopenhag. 1802. Biot, 

 Traite de Physique, and art. Magnetism in Edin. Encyc. Roucher-Deratte, Traite 

 sur 1'Electr. &c. 1803. Meissen, Ueber den Mag. 1819. Barlow's Essay on Mag. 

 Attractions, 1823. Peytavin, Essai sur la Constit. des Fluides Magnetiques, 1830. 

 Brewster's Magnetism, 1837 ; also an essay in many treatises on electricity. 



Memoirs. Du Fay, Hist, et Mem. 1728, p. 355 ; 1730, p. 142; 1731, p. 417. 

 Servington Savery's Mag. Obs. Ph. Tr. 1730, p. 295. Lambert, Hist, et Mem. de 

 Berlin, 1766, pp. 22, 49. Franklin, Am. Tr. iii. 10. Krafft, Com. Petr. xii. 276. 

 Kirwan, Ir. Tr. vi. 177. Ritter, Gilb. Ann. iv. 1. Kratzenstein, Lichtenb. Mag. 

 iv. 132. Poisson, Mem. de 1'Inst. 1821, pp. 247, 448. Ampere, ibid. 1823, 

 p. 175. Harris, Ed. Tr. vol. xi. Christie, Ph. Tr. 1828, p. 325. Blondeau, Mem. 

 de Brest, i. 385, 401. Haldat, Mem.de 1'Acad. de Nancy, 1830. . 1839 ; Ann. 

 de Ch. xlii. 53. Scoresby, Jameson's Jour. 1832, p. 319, &c. Kupfer, Ann. de 

 Ch. xxxvi. 50. 



Artificial Magnets. Leuwenhoek on the Mag. Quality acquired by Iron after 

 standing a long time in the same Posture, Ph. Tr. xxxiii. 72. Marcel, ibid. 

 1730, p. 112. Reaumer, Hist, et Mem. 1723. Duhamel, ibid. 1735, 1745, 

 p. 181. Knight's Method, Ph. Tr. 1744-5, pp. 161, 361 ; 1776, p. 591 ; 1779, 

 p. 51. Canton, ibid. 1751, p. 31. Michell on Artificial Magnets, Camb. 1751. 

 Klingenstierna, De Mag. Artif. Stock. 1752. Riviere sur les Aimans Artificiels, 

 1752. Richmann, Nov. Com. Petr. iv. 235. Nebel, de Mag. Artif. 4to, Utr. 1756. 

 Antheaulme sur les Aimans Artificiels, 1760. Coulomb, Mem. de 1'Inst. vi. 399. 

 Barlow, Ed. Jour. i. 344. Scoresby's Exp. on the Development of Magnetical 

 Properties in Steel and Iron by Percussion, Ph. Tr. 1820, p. 241. Baden Powell, 

 Ann. of Phil. 1822, p. 92. Weber, Magnetismus des Eisens durch die Erde, Res. 

 des Mag. Ver. 1841, p. 85. 



* Ann. deCh. xxvii. 363 ; xxviii. 325 ; xxxii. 213. 



