8 Barrett, Brown, & Haprirnp—On the Magnetic and Electric 
examine this matter more thoroughly the permeability of these silicon alloys was 
compared with that of our best and purest specimen of iron,S. C.I., by a wholly 
different method, employing for this purpose the new and ingenious apparatus 
devised by Professor Ewing, and known as his Permeability Bridge. The results 
are shown in fig. 2, where the curve marked 898 E. is a 24 per cent. silicon-iron 
alloy ; 898 H is a 53 per cent. silicon-iron alloy, and 120 Lis the standard curve 
supplied with the instrument of a specimen of good soft iron determined by Professor 
Ewing, and §.C.I.is our pure Swedish charcoal-iron, all the specimens being 
annealed. From these curves the following table of permeability, » = B/H, is 
obtained. 
TABLE III. 
Comparison oF Macneric Inpuction (B) AnD PERMEABILITY (1) IN THE PUREST 
SwepisH CuHarcoat-Iron (S.C.I.) anp mn Sinicon-Iron Attoys In DIFFERENT 
FYELDS, AS DETERMINED BY Ewine’s BrinGe. 
S. Ge i | 898 E. (24 per cent. Si.) 898 H. (53 per cent. Si.) 
He B K B. | 0 | B. be 
2:0 7,120 | 8,560 | 8640 | 4,320 | 4,400 2,200 
| | 
3-0 | (520 8,173 | 10,400 | 8,466 | 7,600 | 2,588 
| | | 
4-0 | 10,800 | 2,689 11,680 | 2,920 | 9,360 | 2340 
5:0 | 11,680 2,336 12,500 2,500 | 10,400 2,080 
6-0 | i800 | 9078 || 1a~AG 2,173 11,040 1,840 
8:0 | 13,360 Lem | imi | 1790 12,000 1,500 
| 
10-0 eel 20CORmm 1,400 | 14,240 | 1,424 12,640 1,264 | 
| : | 
It will be seen that the magnetic permeability of the 21 per cent. silicon-iron 
is greater than iron up to a field of about 10 to 15 units. These results are so 
remarkable, and of such great practical importance, that it was desirable to 
test this conclusion still further. The specimens used in the Ewing’s bridge 
were in the form of short cylindrical rods 18 ems. long, and 0:91 ems. diameter, 
coupled with a yoke of soft iron. The test rod is balanced against a standard 
rod by varying the strength of the magnetic field round it until the induced 
magnetism is the same in both rods, this equality being indicated by a magnetic 
needle; andthe ratio of the permeability of the test rod to the standard is shown 
by the relative strength of the field required to bring about this equality. This 
arrangement does not enable the cyclic curve to be obtained, and consequently 
the relative hysteresis of the specimens cannot be found by it. 
Another set of experiments were therefore made with the magnetometric method ; 
