Table 297. 



MAGNETIC PROPERTIES OF IRON IN VERY WEAK FIELDS. 



The effect of very small magnetizing forces has been studied by C. Baur " and by Lord Rayleigh.t The following 

 short table is taken from Baur's paper, and is taken by him to indicate tliat the susceptibility is finite for zero values 

 of // and for a finite range increases in simple proportion to //. He gives the formula A-= 15 + too //, or / = 

 15/^4-100 H'-. The experimt;nts were made on an annealed ring of round bar 1.013 cms. radius, the ring having 

 a radius of 0-432 cms. Lord Rayleigh's results for an iron wire not annealed give /t = 6.4 + 5.1 //,or/ = 6.4Af 

 -J- 5. J //=. Tlie forces were reduced as low as 0.00004 c. g. s., the relation of k to H remaining constant. 



Tables 298, 299. 



DISSIPATION OF ENERGY IN GYGLIG MAGNETIZATION OF MAGNETIC 



SUBSTANCES. 



When a piece of iron or other magnetic metal is made to j^ass through a closed cycle of 

 magnetization dissipation of energy results. Let us suppose the iron to pass from zero magneti- 

 zation to strong magnetization in one direction and then gradually back through zero to strong 

 magnetization in the other direction and thence back to zero, and this operation to be repeated 

 several times. The iron will be found to assume the same magnetization when the same magne- 

 tizing force is reached from the same direction of change, but not when it is reached from the 

 other direction. This has been long known, and is particularly well illustrated in the permanency of 

 hard steel magnets. Tiiat this fact involves a dissipation of energy which can be calculated from 

 the open loop formed by the curves giving the relation of magnetizatioi^ to magnetizing force was 

 pointed out by Warburg X in iS8i, reference being made to experiments of Thomson, § where such 

 curves are illustrated for magnetism, and to E. Cohn, || where similar curves are given for thermo- 

 electricity. The results of a number of experiments and calculations of the energy dissipated 

 are given by Warburg. The subject was investigated about the same time by Ewing, who pub- 

 lished results somewhat later. If Extensive investigations have since been made by a number of 

 investigators. 



TABLE 298.- Soft Iron Wire. 

 (From Ewing's 1885 paper.) 



* "Wicd. Ann.'' vol. xi. 



X " Wiod. Ann." vol. xiii. p. 141. 



II " Wied. Ann." vol. 6. 



«« 



Smithsonian Tables. 



TABLE 299- — Calile Transformers. 



This table gives the results obtained by Alexander Siemens with one of 

 Siemens' cable transformers. The transformer core consisted of 900 

 soft iron wires i mm. diameter and 6 metres long.** The dissipation 

 of energy in watts is for 100 complete cycles per second. 



t " Phil. Mag." vol. xxiii. 

 Phil. Trans. Roy. Soc' 



vol. 175. 

 II " Proc. Roy. Soc.'*" 18S2, and " Trans. Roy. Soc." 1885. 

 Proc. Inst, of Elect. Eng." Lond., 1892. 



280 



