( 658 ) 
As regards the ferromagnetism of manganese, this had already 
been observed by Skckklson *) with electrolytic manganese which was 
liberated at ICKT C. from the chloride upon a platinum wire, and 
with a regulus prepared by Bunsen from manganese fluoride. The 
very indefinite observations concerning the magnetization which he 
published do not contradict our measurements. 
By a more direct method we have proved the absence of strong 
magnetism in vanadium, chromium and manganese at low temperatures. 
For this purpose we introduced ellipsoids of the three substances 
into a narrow unsilvered vacuum tube whose walls were separated 
by the smallest possible distance; this was placed in a second similar 
tube also as narrow as possible and filled with liquid air. We then 
determined the distance from the poles such that the ellipsoids were 
attracted from the bottom, of the tube to the poles of the magnet. 
This experiment was made first with the inner tube empty, and then 
with the inner tube filled with liquid hydrogen. The following results 
were obtained: 
Ordinary temperature 
Vanadium I Not attracted 
Manganese j Attracted from distance of 6 to 8 
Chromium as i ., „ „ „ 12 
Chromium b j „ „ „ „ 60 
I In liquid hydrogen 
j | The same as at 
ordinary 
\ temperature 
The results for Chromium b which probably contained a small 
splinter of iron must be rejected. We also found further that a 
crystal of iron sulphate at ordinary temperature was attracted from 
a distance of 25 mm. while in liquid hydrogen it was attracted 
almost from the base of the magnet. Thus the weak magnetization 
of the three metals was found to be practically invariable, while the 
iron sulphate exhibited a very great increase in magnetic properties. 
This experiment is well adapted for displaying the characteristic 
difference' between the two groups of substances and is a typical 
example of the significance which even the simplest experiments 
acquire within the fallow region of very low temperatures. 
§ 2. Methods and apparatus. 
a. Discussion of the method of the maximum couple. We measured 
the intensity of magnetization by measuring the couple exerted on a 
prolate ellipsoid of revolution of the experimental substance arranged 
so that the angle of the field with the major axis of the ellipsoid 
might be varied. The expression for the couple is 
