106 Barrett, Brown & Haprretp—On the Electrical Conductivity and 
Turning now to Plate VIII., we see from the curve for 1179 B, that 
when H is 45, B is a little over 14,000, 
when His 0, Bis 9500, 
when Bis 0, His 8. 
We will now proceed to give a tabulated statement of the results obtained for 
these three magnetic properties, and will first take those carbon steels we have 
tried. The B and H curves for this series were drawn, but are not given in the 
plates, as there is no particular novelty about them, and are retained until the 
series 1s more complete. A more detailed analysis of these and the other steels 
is given under the respective groups in Part I.; all that is here given is the 
percentage of the principal element or elements added to the iron. The test rods 
were, as already stated, 102 ems. long, and varied in diameter from 0:54 to 0°56 em.* 
Unless otherwise stated, the determinations zn all cases refer to specimens in 
the annealed state. T 
Taste Il.—Carbon Steels. 
Mark. | Per cent. of carbon. | 4% gndugiion fo" ererurey eee eee 
| B 0:03 | 17480 | 7120 1-66 
| TAS, | 0:05  ~—-:16920 7400 1:66 
| i166 | 0-14 16800 7420 2-00 
at | 0:58 16280 9040 2°56 
eIsueeal 100 | 14640 8680 6-43 
| GI 1:25 14640 8840 6-43 
The specimen marked B is the best commercial iron, but not quite as low 
carbon as the standard specimen 8.C.I.; this latter not having been procured 
until after most of the magnetic determinations were made. The values obtained 
* In rods of high permeability, having this ratio of length to diameter (about 200 to 1), a correction is 
necessary for the values of the retentivity and permeability given in our tables and curves. Ewing has 
shown (Phil. Trans., 1885, Part II.) that whilst the ‘‘on’’ curve—marked 1 in fig, 8—even in a soft-iron 
rod of 200 diameters is not much below the true value of that given by a much longer rod or ring; the 
“¢ off? curve—marked 2 in fig. 8—is notably different as it approaches the point where it cuts the vertical 
axis at R, fig. 8. Here the demagnetising influence of the ends becomes apparent, and the result in soft- 
iron is to reduce the residual induction, or retentivity, about 40 per cent., compared with an endless rod 
orring. We have not applied this correction, as the amount varies with the permeability of each specimen, 
A fair approximation to the true value can be found by inclining to the right, through a small angle, the 
vertical axis, OB, in the curves, Plates III. to IX. (See Note A at end of this Paper.) 
+ The absolute values of the maximum induction given in our Plates and Tables are a little too 
high, as explained in Note B, p. 126. The word ‘‘retentivity’’? must be understood to be the res¢dual 
induction after our maximum field of 45 units has been reduced to zero, 
