285 



strength of field for coiitiolliii^- the \aliie^ dei'ived tV(~>m ballistic 

 calibrations. I hope to return to the details of the nieasurenients 

 and the arranp;ement of the apparatus afterwards, when an accurate 

 quantitative couipai-ison of the results with Langevin's theory will 

 have been made. It is as yet impossible to decide, in how far 

 deviations are present which might be atti'ibuted to the existence 

 of a small zero-poiut enei'gy which would manifest itself in the 

 manner in which the saturation changes, as well as in a deviation 

 from Curie's law at weak fields. It seems, however, that these devia- 

 tions are not sufficiently large to disturb the general aspect. 



On this occasion I wish to confine myself to communicating the 

 general aspect of the results as laid down in the adjoining graphic 

 representation on which the experimental numbers ma}' also be read 

 with sufficient accuracy. The curves represent the observed attractive 

 force as a function of the square of the field on the axis between 

 the poles. This field was read as a function of the current from a 

 calibration curve. 



r 



Curve I refers to 20.' 3 K. curve 11 to 14,7 K. Ill to 4.°25 K. and 

 IV to l.'^O K. Each division along the horizontal axis corresponds to 

 about 90 kilogauss, along the vertical axis to 25 grammes. The ratio 

 of the force to the square of the field on the axis of the poles per 

 unit of susceptibility was about \ j,, neglecting smalT changes in the 

 topography of the field. 



