2 Barrerr, Brown & Hapripip.—On the Magnetic and Electric 
oo 
heat treatment, and were specially marked. The method of magnetic measurement 
adopted was the “‘magnetometric method,” the rods being placed ina magnetising 
solenoid as described in our former paper. This is the most rapid and convenient 
form of measurement, and for comparative purposes does very well, but it is not 
suited for exact absolute measurements. Hence in the case of a few highly 
permeable specimens the ballistic method was adopted, the specimens being 
made into the form of rings which were carefully annealed and wound with 
primary and secondary coils. Another set of experiments were also made 
with these highly permeable alloys forged and turned into the form of short 
cylindrical rods, so that they could be tested by the “yoke method ” in Ewing’s 
permeability bridge. The results of these comparative tests will be given in this 
paper. A still further comparison was made by turning some of the original long 
metre rods down to a much smaller diameter, keeping their length the same, and 
after annealing, again testing them by the magnetometric method. These 
precautions were only necessary in specimens of very high magnetic permeability ; 
with the non-magnetic or nearly non-magnetic alloys, with which we will deal 
first, one method is nearly as good as another, provided a uniform magnetic field 
can be obtained. These latter specimens were therefore in the form of the 
original rods 102 cm. long and 4 cm. diameter. 
(A)—Iron ALLoys NEARLY oR wHoLLy Non-Maceveric. 
In previous papers we have shown that the addition of certain elements 
to iron rendered the alloy,practically non-magnetic, and we gave a list of seven 
such alloys, reserving to a subsequent paper the fuller examination of this part of 
our subject.* This we now bring before the Society. 
In the accompanying Table I. is given the percentage composition of a series 
of iron alloys or steels which, even when carefully annealed, are non-magnetic 
ina field which nearly saturates pure iron. Employing a delicate reflecting 
magnetometer, and increasing the strengtn of the magnetic field seven-fold, viz. to 
320 C.G.S. units, a slight magnetisation was observed in some of the specimens ; 
the minute magnetic susceptibility thus revealed was measured, and the 
result is given in the table. The first column gives the mark attached to 
each specimen at the Hecla works; then follows the result of the chemical 
analysis, the iron being estimated by difference ; then the intensity of 
magnetisation, I, in a field of 8320 C.G.S.—the best soft iron has an intensity 
of about 1600 in this field. 
It must be remembered that all the specimens in Table I. were very carefully 
annealed, a few duplicate specimens were left “as rolled,” not annealed nor 
specially hardened ; these are marked “ Un.” 
EIS, IID ISE) WOll, Vato, jo LAO, 
