704 
Every registered curve can serve for the determination of a point 
of the curve that indicates the relation between rate of crystallisa- 
tion and boundary temperature. The sum of the temperature of the 
thermostat and the rise of temperature following from the curve, 
gives the boundary temperature. The temperature of the thermostat 
and the dimensions of the tube determine the velocity of erystalli- 
sation, which can be derived from the results of the measurements 
carried out with this purpose (p. 698). 
In fig. 4 the abscissa is the temperature of the boundary plane 
of the phases and the ordinate the velocity of crystallisation. As 
appears from the figure, the temperature does not reach the melting- 
point (42°) in any of the measurements, but always remains far 
below it’). The observations yielding temperatures of the boundary 
above 29° are of no value in consequence of the phenomenon 
mentioned on p. 698, hence they have not been reproduecd in fig. 4. 
When one wants to determine the portion of the curve above 29°, 
another experimental method must be followed, in which the process 
of soliditication has a mathematically defined course also near the 
melting-point, and does not depend on accidental disturbances. 
I am greatly indebted to the instrument maker of the Physical 
Laboratory, Mr. G. KoorscriJN, for the trouble he has taken boring 
the holes in the tubes used by me. 
Institute for Theoretical Physics. 
Utrecht, June 1920. 
1) J. Perrin, Ann. de Phys. Tome XI, serie 9, p. 96. 1919. 
