PHYSICS: P. W. BRIDGMAN 
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is concave toward the pressure axis, and rises continuously, and the 
two known falHng melting curves are also concave downward. We have 
here examples of rising and falling curves with curvature in either direc- 
tion, curves with a maximum temperature (HgL), and curves with a 
maximum or minimum pressure (H2O and Benzol). No cases have 
been found of a critical point, however. In the diagrams several curves 
are indicated as coming to an end; this simply means that for one reason 
or another further measurements were impossible. The relatively 
high frequency of falling transition curves is in contrast to the case for 
melting. A falling curve means that the phase stable at the higher 
temperature has the smaller volume. There are only two known cases 
for melting, whereas more than one quarter of the cases above are of 
