58 Profs. J. Dewar and J. A. Fleming. Changes produced in 



enabled any angular displacement of the magnetometer needle to be 

 easily determined. The position of this magnetometer needle was 

 regulated by the field produced by an external controlling magnet. 

 The small magnet, the behaviour of which at low temperatures was 

 to be studied, was placed behind the magnetometer, with its centre at 

 a distance of 1 to 10 cm. from the centre of the magnetometer needle 

 and its axis in a direction passing through the centre of the magneto- 

 meter needle, and at right angles to the direction of the undis- 

 turbed magnetometer needle. The magnet to be examined was fixed 

 to a brass wire, held in a wooden support in such fashion that the 

 magnet under examination could be easily removed from its position 

 behind the magnetometer, and restored to it again exactly. A large 

 number of samples of steel and iron were then prepared in the form 

 of small needles, generally 15 mm. long and about 1 mm. in diameter. 

 These steels comprised nickel steels, with various percentages of 

 nickel; chromium steels, with various percentages , of chromium; 

 aluminium steels, with various percentages of aluminium ; tungsten 

 steels, manganese steels, silicon steel, ordinary carbon steels in 

 various states of tempering, soft-annealed transformer iron, soft- 

 iron wire, and the same irons hardened by hammering. For most 

 of these samples of steels we were indebted to Mr. R. A. Hadfield, 

 of Sheffield, who kindly furnished them* to one of us in the form of 

 wires. 



These short steel magnets were then all magnetised to " satura- 

 tion " by placing them for a few moments between the poles of a 

 powerful electro -magnet. One by one they were then placed .in 

 position behind the magnetometer, and the deflection produced on 

 the magnetometer needle observed. In any particular case this 

 deflection may be taken as approximately representing the intensity 

 of magnetisation of the sample, although, owing to the varying sizes 

 of the sample and distance from the magnetometer, the deflections in 

 the case of different magnets are not comparable with one another, 

 and cannot be taken as indicating the relative intensities of mag- 

 netisation of two different samples. This, however, was not impor- 

 tant, as our object was not to compare the absolute values of the 

 magnetisation of different classes of steels, but to observe the mode 

 of variation of the magnetisation of any one sample when cooled 

 from ordinary temperatures down to the temperature of liquid air. 



The method of proceeding was then as follows : Having adjusted 

 the image of the lamp filament to the zero of the scale, the small 

 magnet under observation was placed behind the magnetometer, and 

 the deflection of the magnetometer needle observed. A small 

 vacuum-jacketed cup, filled with liquid air, was then brought up 

 underneath the sample, and by its aid the magnet cooled suddenly 

 in situ to a temperature in the neighbourhood of 186 C. In the 



