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Proceedings of the Royal Society of Edinburgh. [Sess. 
of free copper in the alloy may at least play a not unimportant part 
in determining the magnetic behaviour of the bronze. That manganese 
is also an important factor is unquestionable, as its omission destroys the 
remarkable properties of the bronze just as the exclusion of the copper 
would do. It should be noticed, in support of the view here adduced, that 
the liquid air effect in the Heusler alloy increases in magnitude with 
increasing copper content, and hence probably with increasing amount of 
free copper. 
The investigations described in this paper have been carried out in the 
Physical Laboratory of the University of Glasgow, and the authors desire 
to express their thanks to Professor Gray for the facilities he gave for the 
carrying out of the work. 
Summary. 
1. Manganese-aluminium bronzes exhibit less hysteresis, but are also 
less magnetic, after quenching. 
2. Such alloys, if rich in copper, are more magnetic at — 190° C. than 
at 15° C. 
3. Continued baking at steady temperatures reduces the susceptibility 
and increases the hysteresis towards definite limits. 
4. These effects are not simply related to the temperature of baking. 
5. The liquid air effect in baked specimens is often (especially for low 
fields) of opposite sign to that in the virgin alloy. 
6. In Heusler alloys containing 76, 62, and 55 per cent, copper 
respectively, and the remainder manganese and aluminium in atomic 
proportions, the critical temperatures are 280°, 500°, and 345° C. 
7. The quenching and liquid air effects in the Heusler alloys are very 
similar to those in Cu 3 A1 modified by effects due to the presence of free 
copper and free manganese. 
(Issued separately May 3, 1909.) 
