404 Proceedings of the Royal Society of Edinburgh. [Sess. 
Scope of the Investigation. 
The present paper gives an account of some work carried out by the 
author. The following points were investigated : — 
(1) The magnetic properties of the alloy at temperatures lying between 
0° C. and 400° C. (about the critical temperature of the material). 
(2) The alteration in magnetic properties brought about by heating and 
cooling the material. 
(3) The magnetic properties of the alloy at low temperatures in the 
quenched condition. 
Specimens. 
The specimens experimented upon had the following composition : — 
25 per cent, manganese, 125 per cent, aluminium, a trace of lead, and the 
remainder copper. It will be seen that the manganese and aluminium were 
present in atomic proportions, a condition which was shown by Heusler 
to result in a material possessing maximum permeability for a given 
amount of dissolved manganese. The specimens were in the form of 
cylinders, and were tested in the condition which resulted from the 
dressing operations. 
Arrangement of Apparatus. 
The magnetometric method was adopted throughout, and the arrange- 
ment of the apparatus is shown in Diagram I. The specimen was placed 
within the magnetising solenoid S. Connected in series with the solenoid 
was a large circular balancing coil C, placed with its plane perpendicular 
to, and its centre coincident with, the axis of the solenoid. Also on the 
axis of the solenoid, and beyond the coil C, was the magnetometer needle, 
the movements of which could be observed by means of a lamp and scale in 
the usual way. The coil and solenoid were connected through a reversing 
key K with a battery B, an ampere-meter A, and a variable resistance 
R. The stands carrying the magnetometer, solenoid, and coil moved in 
grooves as shown in the diagram, an arrangement which admitted of the 
preliminary adjustments being carried out with great convenience and 
rapidity. 
Description of Electric Furnace. 
In order to study the behaviour of the material when at temperatures 
considerably above that of the room, an electric furnace was contrived. A 
