PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. 103 



that it would be. The subject interested many investigators,^ who 

 found it easy to exhibit the disturbing effects of eddy currents in 

 hindering rapid magnetic changes in solid masses of iron and in 

 thus modifying the characters of the induced currents ; but it was not 

 until much work had been done by many persons on the phenomena 

 attending magnetic induction in iron that the theory of the alternate 

 current transformer which had meanwhile come to be of much 

 practical importance was very well understood. With the general 

 introduction of dynamo-electric machinery the magnetic behavior of 

 the different kinds of iron used in its manufacture became of practical 

 interest, and several different magnetometric and ballistic methods of 

 studying permeability were invented and employed in making the 

 necessary measurements upon relatively small pieces of the metal. 



Soon after the first hysteresis diagrams had been obtained as a 

 result of experiments either on comparatively thin iron or steel rings, 

 or on long, fine wires, it was found by engineers that, on account 

 of the considerable time required to establish a steady current in 

 the coil of a large electromagnet to which a given electromotive force 

 had been applied, the " reversed current," and even the " step- 

 by-step " ballistic methods which had proved effective in the cases 

 of slender toroids, were, in their old forms at least, not well fitted 

 for studying the magnetic properties of such massive closed iron 

 circuits as frequently occurred in practice. When there was a 

 gap in such a circuit, the problem, of course, offered no difiiculty, 



« Faraday, Researches, 1831, 1832, 1846. Lenz, Fogg. Ann., 31, 1834. Henry, 

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 1838 ; 54, 1841 ; 56, 1842. Beetz, Fogg. Ann., 102, 1857 ; 105, 1858. Fliicker, 

 Fogg. Ann., 87, 52; 94, 1855. Rayleigh, Phil. Mag., 38, 1869; 39, 1870; 23, 

 1887; 22, 1886. Bichat, Ann. de I'ficole Norm., 10, 1873. Sinsteden, Fogg. 

 Ann., 92, 1854. Magnus, Fogg. Ann., 38, 1836 ; 48, 1839. Schneebeli, Bull, de 

 la Soc. des Sc. Nat. de Neufchatel, 11, 1877. Blaserna, Giornn. di So. Nat., 6, 

 1870. Maxwell, Electricity and Magnetism, 2, iv. Donati and Foloni, N. Cimento, 

 13, 1875. Stoletow, Phil. Mag., 45, 1873. Auerbach, Wied. Ann., 5, 1878. Row- 

 land, Phil. Mag., 46, 1873 ; 48, 1874. Thomson, Phil. Trans., 165, 1875. J. 

 Hopkinson, Phif. Trans., 176, 1885. Von Waltenhofen, Fogg. Ann., 120, 1863. 

 Warburg, Wied. Ann., 13, 1881. Wiedemann, Lehre von der Elektricitat. Ewing, 

 Phil. Trans., 176, 1885; Froc. Roy. Soc, 1882, Magnetic Induction in Iron and 

 other Metals. Du Bois, The Magnetic Circuit. Fleming, The Alternate Current 

 Transformer. Ewing and Low, Froc. Royal Soc. 42, 1887 ; Phil. Trans., 180, 

 1889. Du Bois, Phil. Mag., 1890. Oberbeck, Wied. Ann., 22, 1884. J. and E. 

 Hopkinson, Phil. Trans., 177, 1886. Jouaust, Compt. Rend., 139, 1904. E. Hop- 

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