C 158 ) 
In the second place, the suppositions concerning the mechanism 
of phosphorescence which were developed in “1904” could be pul 
to the test and extended, if we succeeded in observing any influence 
of the magnetic field upon the phosphorescence bands. That such 
an influence cannot be detected at ordinary temperature has been 
known for years by P Lenard, who for this purpose investigated 
CaBi-, CaMn- and CaNi-“phosphors” in strong magnetic fields. And 
as all bands at ordinary temperature are very broad and ill-defined 
there seemed to be no chance of making further discoveries in this 
direction. Now, however, it had appeared from the above mentioned 
experiments in liquid air, that all phosphorescence bands become 
remarkably narrower and sharper as the temperature is lowered 
(“1904” p. 455), and it seemed to be worth while examining if 
perhaps, at the temperature of liquid — or otherwise of solid — 
hydrogen the narrowing of the bands should continue so far, that 
a further investigation in the magnetic field would afford a new 
outlook upon the problem. 
Indeed, the researches of H. and J. Becquerel and H. Kamerlingh 
Onnes upon the phosphorescent uranyl salts, completed last year 
and published 1 ) after the present investigation had been commenced, 
were successful in this respect. 
and it was remarked that the magnetic field should exert a similar influence as 
that exerted by temperature upon the transition of the electrons from one state 
to another. 
This image was further developed in later researches by J. Becquerel and H. 
Kamerlingh Onnes (Comm. N°. 103, Febr. 1908, particularly pp. 595, 597—598,602) 
on the absorption-spectra of compounds of the rare earths and their behaviour in a 
magnetic field, which were undertaken also on account of the particular influence 
of liquid hydrogen temperatures upon the effect of forces exerted by ponderable 
matter upon the electrons. As “gas or vapour” state can be distinguished that 
state of motion in whiph thfe electrons can occasion conduction of electricity 
through the atoms when these are in metallic connection, by “liquid”, a state of 
motion in which they are sensitive to light-vibrations and absorption phenomena, 
while, on the other hand, a “solid” state is a state of motion in which they can 
take part neither in conduction, nor in absorption of light. 
Interpreting the results of the experiments just mentioned in terms of this 
theory we find that by the c : rcumstance that at very low temperatures the sphere 
of influence of the dynamids extends to a greater distance the free path in e 
electron vapour is greatly diminished, and that hydrogen temperatures are already 
sufficiently low to cause the electrons at various parts of the atom to assume the 
solid state; these are just the places where the electrons at temperatures that are 
not so low are particularly numerous in the liquid state, as can be seen from 
occurrence of various absorption bands. 
9 H. and J. Becquerel and H. Kamerlingh Onnes, Comm. Physic. Lab. ‘Leiden. 
N°, 110. These Proc. May 1909. 
