1888.] Recalescence of Steel, and allied Phenomena. 177 
opposed to ‘cold’ steel. This EMF. cannot be explained by re- 
ference to the Thomson forces, unless they are of such a kind 
that summed round a circuit they do not disappear. 
Magnetic susceptibility in cooling steel and «ron. 
Many experiments have been made on this point: but it 
appears that in far the greater number of these no pure results 
could be obtained, because the magnetometer used has in general 
been too refined for the method of heating and cooling em- 
ployed. 
There can be little doubt that above a certain temperature 
steel and iron do not differ from air in magnetic susceptibility. 
The doubt is as to the mode of appearance as temperature falls. 
Most experimenters find that there is at first a gradual accession, 
then a sudden rush, so to speak, and afterwards a gradual increase 
of magnetic susceptibility. My own impression is that the first 
gradual accession is in reality due to unequal cooling. The 
greater the precautions to secure equal cooling throughout the 
mass of steel used, the more does the first gradual accession 
diminish. 
I have experimented with small spheres of metal sunk into 
a thick brass rod, the rod being cut in two, the ends faced and 
a hemispherical hole made in each, so that the sphere of steel 
or iron might be gripped between the two faces and heated in 
the brass. 
The appearance, during cooling, of magnetic susceptibility is 
very much more leisurely in steel than in soft iron, and it is most 
curious to observe how the rate of appearance entirely corre- 
sponds with the rate of reglow. In all cases where I failed to 
detect reglow, the iron became magnetic with a flash, as it were, 
so that the magnetometer needle was deflected with a kick, 
carrying it much beyond the new position of rest. With specimens 
of hard steel in which reglow was very slow, the magnetometer 
needle moved slowly and almost without any swinging up to its 
new position. 
A strong steel bar magnet was held perpendicular to the 
magnetic meridian and the small magnetometer needle was then 
set so as to be almost at the neutral point in the resultant field 
of the bar magnet and LEarth’s horizontal component, only 
enough displacement being given to direct the needle conve- 
niently for lamp and scale reading. Then an unmagnetised 
sphere of soft iron was moved about near the magnetometer, and 
the spot was settled experimentally where the maximum effect 
on the magnetometer needle was observed. This spot was 
marked by lining with fixed objects, and the brass rods fixed 
