804 



as it appears after our inoditiration. is shown in section and seen 

 from above. The lower part remained nnehanged '). 



The arranorement here described has some advantages over that 

 with the electro-magnetic compensation. In tiie first place, a much 

 greater foi'ce S can be measured by it, and moreover the method 

 of working is simpler, as now only one current (that of the electro- 

 magnet) has to be read, in the earlier arrangement three. On the 

 other hand, while in the former arrangement the current through 

 the electro-magnet was adjusted to certain tixed values, for which 

 the corresponding strengths of field were accurately measured, in 

 the modified arrangement it is best to place a cei-tain weight upon 

 the scale, and to regulate the current through the electro-magnet, 

 until this weight is exactly compensated by the force exerted upon 

 the experimental substance by the magnetic field. As the strength 

 of field corresponding to this current must now be found by (graphic) 

 inlerpolation, it can now only be as accurately ktiown as by the 

 method' described in Comm. N". 139", if the field has been determined 

 for a great number of current strengths. Naturally in the method 

 of compensation by weights we could also work with a few accurately 

 measured magnetic fields, if we had a sufficient number of snuill 

 weights at our disposal inside the apparatus; but working in this 

 way would greatly decrease the simplicity of the method. For this 

 reasoii in these investigations by the method of compensation with 

 weights, the field for the Weiss electro-magnet for different strengths 

 of current, was very minutely studied. 



Physics. — "Magnetic researches. XII. The susce[)tlblllty of solid 

 oxygen in two forms'. By Albert Perkier r^t/ic/ H. Kamerj.ingh 

 Onnes. Communication N" i39c from the Physical Laboratory 

 at Leiden. (Communicated by Prof. H. Kamerlingh Onnes. j 



(Communicated in the meeting of January ol, 1914:.) 



§ 1. Introduction. A former investigation '') had led us to the 

 conclusion that the susceptibility «of oxygen suddenly becomes consid- 

 erably smaller when this substance changes into the solid state. 



1) The sectional drawing of the upper portion of the apparatus is drawn on 

 the same scale as the fig., in Comm N*^. 139a, and gives therefore, if placed upon 

 that, the complete drawing of the apparatus as used in the researches of Comm. 

 N*J. 129Ö, 132e and Void. 



~ H. Kamerlingh Onnes and Albert Perrier, Leiden Comm. N'. lL6andr24a. 



