efore my departure for Greenland in 1906 Dr. K. J. V. STEEN- 
B STRUP had asked me to take light-measurements with the 
photometer constructed by him. But as, at first, we had enough to 
do with superintending the pioneering work at the Arctic station, 
scientific observations had to be laid aside for a time. 
Not until the summer of 1907 was the photometer set up, and 
since the spring equinox, 1907, it has been regularly used. 
STEENSTRUP ! has described very fully and figured his photo- 
meter, so here I need only give a short description of the method 
of use. — А slip ofithe sensitive paper “Eastman Solia, white blank” 
is placed in a long zinc trough and covered with a number of 
slips of unequal length of a kind of tracing-paper, with a piece 
of glass over all.. This is all put into a thick glass-tube, together 
with pieces of chloride of calcium to prevent the deposition of 
moisture; the tube is closed with an india-rubber cork, and is 
exposed to the light upon a suitable structure for a certain time. The 
light then penetrates a varying number of slips of tracing- paper 
and produces upon the sensitive paper a graduated series of tints. 
The number thus penetrated by that light which left the faintest 
visible record forms a standard of light-intensity. In the following, 
we will call this figure the actinometer number. 
The method just described has since been investigated physically 
by Professor К. Prytz who also obtained the transmission - coeffici- 
ents of the paper used by STEENSTRUP, as well as the relative intensity- 
values of the actinometer numbers. К. Prytz and A. PAULSEN? have 
been discussing the value of this method and of photographical light- 
measuring methods in general. And finally STEENSTRUP® has published 
some results obtained by his method, to which we shall return later, 
but unfortunately any comparison with WIESNER’s exceedingly ex- 
haustive light-investigations, made by another method but on similar 
principles, is wanting. 
173 See list of literature at the end of this paper. 
