813 
below 3°/, of the total blackening. In fig. 1, to begin at the top, the 
curves are represented corresponding to the absorption spectra 
respectively of the phases: isotropic-liquid, ex-solid and ex-liquid; 
four different photographs of the same spectrum of absorption on 
one plate provided the material for every one of these curves and 
are marked by four different signs. 
120. - ° ed 
“oO 
4713 
o o o fo) fe) o o 
ro) Pon o > o oO A 
+ = roy ~ oO t a 
© © ay wo o o o 
4980 
4790 
— blackening. 
5210 
5090 
— wavelength. Fig. 1. 
The difference in optical conduct between ex-solid and ex-liquid, 
found already for ultra-red rays, proves also to exist for the visible 
spectrum. In the same way the blackenings for the screens are 
explained in drawing. Out of the curves obtained in this way, for 
each definite wavelength the blackening is measured for the successive 
screens; and by means of the known faculty of transmission of the 
screens, marked as function of the light-intensity (fig. 2). 
For 15 different wavelengths the blackenings thus calculated are 
explained in drawing. The faculty of transmission of the screens being 
marked in percentages on logarithmic millimeter-paper, then the 
blackening drawn as function of log. I shows the well-known form of 
the blackening-curve witli the big rectilinear part in the middle. This 
straight part corresponds with blackenings for which the plate is not 
over- nor under-exposed, and the best proportion between time of 
