488 Mr. W. Sutherland on Thermal 



faces of the mica vane and conductivity, ought to have nearly 

 the same value for two gases so closely alike as air and 

 nitrogen ; that is of course on the assumption that the value 

 of c' for oxygen is not much different from that for nitrogen, 

 but we had better delay the discussion of this curious point 

 until we have considered the data for oxygen. 

 For C0 2 and CO the parameters are : — 



CO, 



CO 



c'. 



A". 



B"'. 



1-25 



•000625 



o-o 



1-32 



•000625 



o-oi 



In the case of CO these values give values of the repulsion 

 or deflecting force agreeing closely with the experimental 

 over the whole range of pressure, but for C0 2 the calculated 

 values are larger than the experimental at the higher pres- 

 sures ; but the matter is hardly worth going into more closely, 

 especially as oxygen and hydrogen show exceptional behaviour 

 of the highest interest to which we will proceed. 



For oxygen Crookes obtained the following, the pressure 

 unit being 1/10 6 atmo, and the unit of repulsion the same 

 arbitrary one as before: — 



p 1000 803 658 623 613 



10* log. dec 1102 1093 1088 1086 1085 



def. force 12 12 13 13 13 



p 360 297 190 171 110 



10 4 log. dec 1070 1058 1038 1033 988 



def. force 13 14 20 21 31 



where the deflecting force remains almost constant from a 

 pressure of 1000 down to 297, after which it rises, and at lower 

 pressures than those given attains a maximum and then dimi- 

 nishes. Now Bohr ( Wied. Ann. xxvii.) discovered a remark- 

 able discontinuity in the compressibility of oxygen at about 

 921/10 6 atmo, which has been corroborated by Baly and 

 Ramsay (Phil. Mag. [5] xxxviii.), and obviously the above 

 anomaly must be traced to the same cause as the discontinuity. 

 These phenomena are so important for the chemistry of oxygen 

 that I will discuss them in a separate paper on " Spontaneous 

 Change of Oxygen into Ozone, and a remarkable type of Dis- 

 sociation." Meanwhile we will go on to the region of pressure 

 in which the repulsion in oxygen is not exceptional ; here we 

 have ,/ = 3-0, A"='0007, und B'^'0132, which give the 

 following comparison with the experimental results : — 



