( 1S9 ) 
We have therefore investigated a series of well-defined “phosphors’* 
of the alkaline earths as described in “1904” in liquid and solid 
hydrogen, — hence to a temperature of 14° K. The general result 
we first communicate here: The bands behaved quite as we expected 
in becoming narrower and sharper, so that the wave-lengths of their 
maxima could be determined at these low temperatures under very 
favourable circumstances. But they remained bands whose intensity 
did not support a strong dispersion, and this is the reason that we 
have for the present postponed the continuation of the experiments 
in the magnetic field. Our aim has rather been to study the parti¬ 
cular temperature properties of a number of definite bands, and 
from these we have attempted to draw general conclusions con¬ 
cerning the process of phosphorescence. In this we have found the 
ideas already developed fully supported; in certain respects, however, 
some not unimportant extensions of these conceptions have been 
obtained and hence we publish our results here in full. 
§ 2. Apparatus. The apparatus shown in fig. 1 was used for 
the experiments with liquid hydrogen. The liquid hydrogen is intro¬ 
duced *) through the german-silver tube a to the transparent vacuum 
glass b, which is inserted in a vacuum glass c containing liquid air. 
The gaseous hydrogen is led away through d to the gasometer or. 
the vacuum-pump; e is a safety tube, and at the same time a mano¬ 
meter. The german-silver tube /attached to the german-silver covering 
by means of a packing tube allows a vertical or a rotational motion 
to be communicated to the rod 
By means of 6 X , a steel capillary which enters, the opening of 
the hollow rod and is there soldered, the rod g x g, carries two 
copper plates p xx and p 21 which are provided with small frames 
p 12 p l% on the longer sides. In the copper frames p lt thin glass 
plates q can be fitted, and on these the powdered “phosphors” are 
scattered in a layer of varnish *) and fastened under a very low 
pressure. The front of the frame is provided with numerous incisions 
so that the glass plates can be clamped by bending down the little 
teeth formed in the process of cutting, without exposing the “phosphors” 
to pressure. The two plates p x > p s and the screw and nut at the 
upper end of the smooth rod g enable one to observe different 
b Cf. Comm. N*. 108, Pi. I. fig. 4 ; Comm. N°. 94/*, PI. Ill, Sept. ’06. 
B ) We satisfied ourselves that the varnish used did not phosphoresce even at 
—260° C. At temperatures that were not so very low we had thought of using 
lanoline for attaching the “phosphors”, but it seemed to give rise to an afterglow 
which in one of our substances almost led us upon a false track. 
