277 
1908-9.] Magnetic Properties of certain Copper Alloys. 
deriving the true field from that due to the current in the helix. The 
values of I are obtained on the assumption that the polar distance of the 
cylindrical specimens is their total length — an assumption which has 
been justified by comparison of such specimens with others turned down 
into ellipsoids of revolution. The curve A A shows the magnetic condition 
of the alloy in its original state. On re-testing with the specimen at the 
temperature of — 190° C. the dotted line curve A A' was obtained. The effect 
of cooling to liquid air temperature has been to increase the permeability 
O 80 jq 120 
Fig. 2. 
and raise the saturation-point. The coercive force has been augmented 
but to a very slight degree, while the residual magnetism has increased 
about 30 per cent. After being quenched at 450° C. the specimen was 
almost non-magnetic as indicated by QQ. On cooling, however, to — 190° C. 
there was a marked increase in permeability and hysteresis as shown by 
the curve Q'Q'. Another specimen which had been very rapidly cooled in 
the process of casting gave P and P' respectively for the highest points on 
the 15° C. and the — 190° C. magnetisation cycles. It exhibits a large liquid 
air effect, and therein resembles the quenched material. 
Fig. 2 shows similar tests on alloy E — an alloy much poorer in copper. 
A is the magnetisation curve for the initial condition ; and A' the curve 
obtained when the specimen has been cooled down to — 190° C. The ascend- 
ing and descending limbs of the hysteresis cycle have been omitted, as the 
