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PROCEEDINGS OF THE AMERICAN ACADEMY. 



"reduced" units, the resulting curves will be identical for all five 

 gases. The observations at ordinary temperatures on hydrogen, whose 

 critical temperature is very low, will then correspond to observations 

 at very high temperatures on other gases, and will afford a useful 

 though precarious extrapolation of their curves to above 1000° C. 



Figure 1. Reduced Joule-Thomson coefficient, /*', plotted against reduced 

 temperature. From Buckingham's paper in the Bulletin of the Bureau of 

 Standards, May, 190S. (See the note at the end of this paper.) 



The experimental justification of this use of the law of correspond- 

 ing states is, as yet, meager. Figure 1, which is taken from a recent 

 paper by Buckingham, represents the available data. It will be seen 

 that neither the hydrogen nor the carbon dioxide observations overlap 

 those on the other three gases, and that the points for each of these 



