815 
From the screen-spectra about 10 points are deduced for each 
blackening-curve; as these points have to lie on a tight curve, the 
faults in their situation may be partly neutralised by graphic inter- 
polation, which increases the reliability of the method. In order to 
determine the extinction for a fixed wavelength, the blackening for 
isotropic-liquid, ex-solid and ex-liquid is gathered in fig. 1 and these 
values transmitted on the blackening-eurve of the corresponding 
wavelength. The absciss of the diagram shows immediately the faculty 
of transmission in °/, for the corresponding phases: By means of 
the values thus obtained for the faculty of transmission the absorp- 
tion-curve is constructed for each of the three phases mentioned. In 
fig. 3 the absorption-curves are designed; to begin at the top re- 
spectively for the phases isotropic-liquid, ex-solid and ex-liquid. In 
both the marked series of points the experimental material is laid 
down of two separate preparations each photographed on a separate 
plate; the height of the substance in both cases was the same. 
Suppose now (what surely is not in accordance with the strong 
extinction found) that the relation between incident and transmitted 
light for this substance is given by the known formula of absorption : 
1, = intensity of the incident light 
—hd | / = intensity of the transmitted light 
h =coefficient of extinction 
d = height of the preparation 
ea le 
then we can calculate the quantity “Ad” for the various wave- 
lengths by means of fig. 3. According to the Theory of Dispersion, 
given by Dr. SPIJKERBOER in his dissertation, where it is proved 
that absorption- and extinction-coefficient are mutually additional, 
the obtained quantity “h”’ for each phase = the sum of dispersion- 
and absorption-coefficient. Supposing now that by approximation the 
real absorption-coefficient is the same for the three phases, we find 
in the difference: 
h isotropic — h ex-liquid = A, 
and h isotropic — h ex-solid = h,, 
the extinction-coefficient in its relationship to the wavelength for 
each of the two liquid-crystalline phases. 
In order to find out whether the obtained extinction coefficient is 
proportionate to a power of A, we constructed the curve log h as a 
function of log2. This curve proved not to be straight over its 
whole length, but by approximation could be seen as existing of 
two recti-linear pieces, which showed a different inclination for each 
liquid-erystalline phase 
