700 
The substances with known and unknown conductivity respectively 
are placed between three parallel copper plates. The upmost plate is 
electrically heated, the downmost is cooled with water. The differences 
of temperature between the plates have been measured thermo- 
electrically. The ratio of the conductivity of the two substances is 
found from the differences of the temperature and the thicknesses 
of the layers. When for glycerine the value: 
AS 12.5105 
is taken for the conductivity, the following values are found for 
solid and liquid salol respectively : 
A, == OORD 
Ans 43555, 10-5. 
It is worthy of note here, that the difficulties which are met with 
in measurements of conductivity of heat are greater than those in the 
other measurements which have been mentioned in this paper. Errors 
should therefore, for the greater part be attributed to the measure- 
ments of the conductivity. 
6. The exterior diameter of the tubes used has been measured 
with a micrometer screw. The interior diameter is determined by 
weighing of a quantity of mercury, which has filled a known length 
of the tube. 
The conductivity of glass, which has also influence on the meas- 
ured temperature, has not been determined. For this quantity 
different values have, indeed, been found according to the kind of 
glass that was examined, but the influence of the thermal conduc- 
tivity in the glass wall is comparatively small, so that a mean value 
suffices. For this has been taken: 
1 = LSO: 
By the aid of the results of the said measurements, the tempera- 
ture on solidification in a definite tube can be numerically calculated. 
The measurements having been carried out in a point of the axis 
of the tube, » =O should be put in the formulae. The calculation 
has only been completely carried out for a single case. The compar- 
ison of theory and direct observation cannot yield new results, but 
only corroborate the correctness of theory and observations. 
The tube for which the calculation was made, has as bore: 
a= 0.88 mm. 
The thickness of the glass wall was: 
d= 0:91 nim: 
The temperature of the thermostat was 16° during the observations. 
At this temperature the velocity of crystallisation was maximum in 
