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PROCEEDINGS OF THE AMERICAN ACADEMY. 



curve SO obtained had the characteristics of the curve now given for 0°, 

 but the maximum at the top was much more strongly accentuated than 

 in the present figure. It was surmised in the previous paper that at 

 high enough pressures the internal energy of all liquids would probably 

 increase instead of decrease along an isothermal. This surmise seemed 



2 3 4 5 6 7 8 9 10 U 12 

 5 Pressure, kgm, / cm.^ x 10^ 



Figure 8. The decrease of internal energy of water during an isothermal 

 compression. 



plausible because one would expect that at high enough pressures the 

 energy stored up as strain in the interior of the molecules in virtue of 

 the extremely high pressures would more than counterbalance the 

 work done by the attractive forces of the molecules themselves as they 

 were brought closer together by the action of the pressure. This 

 present figure shows that this is not the case, however, for the range 

 of pressure reached here. The lower temperature, 0°, is the only one 

 at which this reversal of the direction of the change of internal energy 

 manifests itself, and this change, in comparison with the other curves, 

 is now seen probably to be an effect of the other abnormalities shown 

 at low pressures and temperatures. Nevertheless it would still seem 

 as if at very high pressures the energy must increase instead of de- 

 crease along an isothermal, but the only indication of it from the 

 present curves is in the direction of curvature, which is in the direction 



