MAGNETIC APPARATUS. 147 



he had discovered magnetic dip. All these discoveries were 

 intrinsically of fundamental importance, but they do not seem to 

 have become known to those who might have based further 

 advances upon them ; and, conrequently, although the merit of 

 their author is none the less on that account, we cannot trace up 

 to them in an unbroken line of descent what is now known in 

 connection with magnetism. On the other hand, Gilbert's work 

 has never been lost sight of, but has been, ever since its publica- 

 tion, the recognised starting-point of accurate magnetic science. 



In the absence of hardened steel as a familiar material, natural 

 magnets or loadstones formed the strongest permanent magnets at 

 the disposal of the early experimenters. The general introduction 

 of steel magnets for experimental purposes is due to Servington 

 Savery (Phil. Trans., 1730). 



About 1780, Coulomb discovered the quantitative laws of mag- 

 netic force, and laid the foundation of the mathematical theory of 

 magnetism which has been built up by Poisson, Green, Gauss, 

 Thomson, and others. After this date, it does not seem that 

 much progress was made in the experimental study of magnetism, 

 until the discovery oi electro-magnetism by Arago, in 1820,* put 

 an enormously increased source of magnetic power into the 

 hands of experimenters, and the discovery of magneto -electric 



* According to Horner (Gehler"s Physikalisches Worterbuch, vol. vi., p. 

 661, [edit. 1836]) electro-magnets were not generally known in Germany or 

 Holland until 1830, when attention was called to them by Professors Piaff, of 

 Kiel, and G. von Moll, of Utrecht, each of whom had become acquainted 

 with them through visiting the Physical Cabinet of the London University 

 (now University College, London), of which the late Mr. Watkins, of the firm 

 of Watkins and Hill, was at that time Curator. 



Another point which may be mentioned in connection with the history of 

 electro-magnets is that tubular electro-magnets, to which attention has lately 

 been called in this country, were made in Germany in 1850, by Romers- 

 hausen, who found that an external soft iron tube increased the carrying power 

 of an electro-magnet, with an iron core 0-9 cm. in diameter and 8-4 cm. long, 

 64-fold. Electro-magnets of similar construction seem also to have been 

 known in France for many years, as they are described and figured by Daguin 

 (Tta'.ti de Physique [edit. 1861] vol. iii. p. 616), by whom ihey are ascribed 

 to MM. Favre and Kunemann. 



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