862 
blackened photographic plate on radiation of given wave-length especi- 
ally investigations on plates with small and increasing size of the 
grains will be the most interesting. It is in order to get those plates 
with small, increasing grains that we have chosen the plates and 
the developer used. It is seen from fig. 5 that this purpose has been 
perfectly attained. 
In fig. 6 the whole observing mate- 
rial is brought in connection. As inde- 
pendent variable the cross-section of 
© gee! the grain has been chosen, as ordinate 
: the ratio of the resp. blackening and 
the quantity of silver in mg. per 100 
em.” of plate. 
As the grain of plates 3 and 2 has 
EL 
D groen 
O uitraroomn 
been found by interpolation, — these 
030 = points are indicated on fig. 6 by a 
vertical line over the circle — and as 
we accordingly do not know in how 
far this eross-section of the grain is 
accurate, the curves have only been 
continued up to the points obtained 
from the observations of plate 4. 
025 = 
020 =| In the plates 10—4 the mean of the 
values A and B has always been taken 
for fig. 6. 
It is self-evident that with equal 
size and nature of the grains the 
blackening must be proportional to the 
quantity of silver per cm’. SHEPPARD 
06 and Mers), Hurter and DriFFIELD *), 
Fig. 6. Eper*) found this result; in our expe- 
riments this appears not to be the case. This contradiction must 
find its explanation in the fact that the said investigators had equal 
grains in the different blackenings, whereas this was not the case 
with us. 
015 
010 
It appears clearly that really — depends in a high degree on the 
size of the grain, as was derived by Nurrine *). 
1) Zeitschr. f. Wiss. Phot. Bd. 3 1905, p. 282—289. 
*) Jahrbuch f. Photographie und Reproduktionstechnik 1899, p. 219. 
8) Beitrage zur Photochemie und Spectralanalyse Eder und Valenta II, p. 57—58. 
t) Phil. Mag. 1913, Vol 26 p. 425. 
