122 Barrett, Brown & Hadfielti — On the Electrical Conductivity and 



is not very much lower than iron.* As 2 or 3 per cent, of added nickel also 

 improves steel magnetically, it was interesting to see what magnetic effect would 

 be produced in steel by the addition of both silicon and nickel in these per- 

 centages. This is shown in specimens 1103 A and C, which, however, are not 

 as good as the silicon steels alone. 



Owing to the very high permeability of the silicon steels, it was desirable to 

 compare one of them more fully with the jDurest specimen of commercial iron 

 obtainable, containing only 0-028 per cent, of carbon (marked S. C. I.), which 

 specimen, moreover, had been carefully annealed. t For this purpose the 

 specimen 898 H, with 5*5 per cent, of silicon was selected, and the permeability 

 determined with magnetising forces varying from 2 to 40C. G.S. units: the 

 results are given in the next Table. 



Table XVII. — Permeahilitu of Silicon Iron compared with best Wrought Iron. 



It will be noticed that for magnetic fields up to 8 C. G. S. units the permeability 

 of 898 H is higher than nearly pure iron. For weaker fields than the above the 

 permeability of 898 H, as might be expected, compared still more favourably 

 with the best iron. The vertical force of the Earth's magnetic field (0-45 C. G. S. 

 units at the place of observation) produced in 898 H a magnetic induction of 

 1240, and in S.C.I, an induction of 600. For this weak field the permeability 

 of the silicon steel is therefore rather more than double that of the best iron. 



*• Since the foregoing results were obtained we notice that Mr. F. C. Caldwell has recently found that 

 silicon increases the permeability of cast-iron, when present in amounts varying from 1-8 to 4-6 per cent, 

 for inductions up to 8000 C. Gr. S. It does not appear, however, that Mr. Caldwell obtained a permeability 

 higher than that given for Bessemer iron, owing to the nature of the material he employed. — (See Science 

 Abstracts, May, 1899, p. 300, taken from a paper in the Electrical World, an American journal.) 



f The full analysis of this specimen is given in Part I., p. 73. 



