38 



SCIENCE PROGRESS 



8 of about 2 and the compressibility was very sensibly decreas- 

 ing. On the other hand the lowest critical temperature known 

 being that of helium at say 5° K., it follows that a value of 

 6 = iooo makes T = 5ooo° K., a value far above any at which iso- 



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thermal measurements are possible under present conditions. 

 As the critical temperature of hydrogen is about six times as 

 great, it follows that even with 6 = ioo the practical limits are 

 reached with this gas and hence with all others, There are 



