6 Barrert, Brown, & Haprretp—On the Magnetic and Electric 
steel, of good mechanical properties like some of the above, would be in- 
valuable, and where the question of the cost of material is comparatively 
unimportant. 
The conversion of a strongly magnetic body into a non-magnetic one by 
alloying it with another magnetic body is a matter of great theoretic interest, 
and one that awaits full explanation. We have referred in the sequel to some 
considerations which bear upon this matter. 
(B)—Attoys or Iron MorE Magnevic THAN Pure Iron. 
We now pass to the opposite class of iron alloys, wherein we have found, as 
mentioned in our previous paper, that the addition of certain elements, such as 
nickel, silicon, and aluminium, 7zereases the magnetic susceptibility in low fields, 
even of the purest and best iron commercially obtainable. 
(1) The magnetic properties of the alloys of iron with nickel have been 
examined by the late Dr. Hopkinson, F.R.S., and others, but the specimens they 
used contained, as a rule, high carbon, and were really, what they were termed, 
nickel-steels. Hopkinson, as is well known, first showed that high nickel-steels 
could be made to exist at ordinary temperatures in a magnetic or non-magnetic state 
according to the previous heat treatment they had received. The specimens of 
nickel-iron alloys here examined had as a rule a low percentage of carbon and 
other impurities, and were carefully annealed. Rejecting those specimens which 
contained the largest percentage of carbon, the curve of magnetic permeability 
with increasing percentage of nickel is shown in Plate I. It will be noticed that 
in a field of 8 C.G.S. units the permeability rapidly falls after 4 per cent. of nickel 
is added, and the annealed alloy becomes nearly non-magnetic in low fields when 
12 per cent. is reached, but after 25 per cent. a sudden increase of permeability 
occurs up to the highest percentage reached, when 31 per cent. of nickel is 
alloyed with iron. This curve of permeability closely resembles the curve of 
tensile strength and hardness of these alloys which we gave in our former 
mppaperan 
When the nickel does not exceed 3 per cent. the alloy is nearly as good 
magnetically as very soft iron, and when the magnetic field is very low, under 
one unit, the permeability of a 30 or 31 per cent. nickel-iron alloy exceeds the best 
and softest iron. So soft is this annealed high nickel-iron alloy (marked 1449) that 
it is magnetically saturated in a field of 4 units, in fact it is highly magnetised 
when the vertical force of the Earth’s magnetism alone acts upon it, more so in 
this field than the purest and softest annealed iron. But, as will be seen from the 
* Trans. Roy. Dub. Soe., vol. vii., p. 112. 
