292 



Profs. J. A. Fleming and J. Dewar. On the 



Table I. Table of Results of Observations on the Magnetic 

 Permeability of Liquid Oxygen. 



The values of the permeability given in the foregoing table are not 

 all of equal weight. 



The calculated value of JJL 1 depends upon the observed ballistic 

 throw, and this cannot be read to a high degree of accuracy when the 

 throw is as small as 4 millimetres. We consider that the best result 

 is obtained by taking the mean of the values for the primary currents, 

 37'8, 36'8, and 50'5 amperes, and these values give /* = 1*00287, with 

 a probable accuracy of + 0'0002. This value of the permeability of 

 the liquid oxygen corresponds to a magnetising force lying between 

 166 and 220 C.Gr.S. units. It will be seen that this method is best 

 applicable to the determination of the permeability under large 

 magnetising forces ; and that these observations do not, in them- 

 selves, allow us to state whether the permeability is a constant for 

 all forces, or is a function of the value of the force. 



In the next place the value is a relative one. The number 1*00287 

 is the ratio of the magnetic permeability of liquid oxygen to that of 

 the gaseous oxygen nearly at the same temperature resting upon the 

 surface of the liquid. We were not able by this method to detect the 

 difference between the permeability of the cold gaseous oxygen lying 

 on the surface of the liquid oxygen when in quiet ebullition, and which 

 has a temperature of about 182 C., but a density of at least three 

 times that of oxygen at C., when compared with that of gaseous 

 oxygen at ordinary temperature, and under the normal pressure. In 

 a very valuable memoir on the determination of magnetic suscepti- 

 bilities, M. P. Curie* has examined the susceptibility of gaseous 



*.' Theses presentees a la Faculte des Sciences de Paris pour obtenir le grade de 

 Docteur es Sciences Physiques,' par M. P. Curie, Paris, 1895.' This memoir is 

 of remarkable interest in many ways. 



