122 Barrett, Brown & Haprrerp—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 purest 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 40 C.G.S. units: the 
results are given in the next Table. 
Taste XVII.—Permeability of Silicon Iron compared with best Wrought Iron. 
When cea, aes es 
2 1840 2240 
4 2050 2630 
8 1610 1680 
12 1200 1160 
16 965 910 
20 800 745 
30 560 516 
40 435 400 
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 8.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-vron, when present in amounts varying from 1:8 to 4:6 per cent. 
for inductions up to 8000 C.G.8. 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 Scvence 
Abstracts, May, 1899, p. 300, taken from a paper in the Hlectrical World, an American journal.) 
+ The full analysis of this specimen is given in Part I., p. 73. 
