( 161 ) 
that they showed those bands, which will be discussed in the sequel, 
well developed. Phosphorescent zinc sulphide, 'uranyl fluoride fluor- 
ammonium, and a crystal of uranyl nitrate were also examined. 
$ 3. Temperature phases. An ample and comprehensive treatment 
of the change of light emission of the ‘‘phosphors” with temperature 
has already been given 1 ). 
According to that exposition of the subject, to each band of the 
phosphorescent light there belong three phases, which as the temperature 
falls succeed each other in the following order: 1. the upper momentary 
phase, or heat phase, 2. the permanent phase* 3. the lower momentary 
phase or cold phase. For each of the various phosphorescence bands 
the range of temperature embraced by the- permanent phase, which 
also determines the two other phases, lies at a detinite height upon 
the scale of temperatures. In the lower momentary phase the electrons 
which under the photoelectric influence of the illumination are ejected 
from the metallic atom are fixed and stored *) in the neighbourhood a j ; 
in the upper momentary phase this fixing of the electrons does not 
occur for they return immediately causing emission of light; in the 
intervening permanent phase some of the electrons return and others 
are fixed in the neighbourhood. It is this permanent phase in which 
the “phosphor” shows the long and bright afterglow of its respective 
band. In the earlier experiments which reached a temperature of 
only —180 C. the existence of the three phases remained hypothetical 
for a number of bands, but we are now in a position to show that 
for these bands the apparently missing regions of permanency and 
of the lower momentary phase can really be attained by a further 
9 “1904” ; also P. Lenard : Verh. des Naturh. Med. Ver. Heidelberg, 5 Febr. 
1909, pp. 9 f io et seq. We shall in the sequel refer to this comprehensive 
paper as “1909”. 
' 2 ) All the ejected electrons are not thus stored: some of them return at once 
and in this way cause the momentary light during the illumination ; see in this 
connection § 7 of this communication. This “momentary process” happens with 
more or less intensity (according to the exciting wave length) alongside the second 
process of storing the electrons. It was in a former paper (“1904” p. 667) con¬ 
sidered as an extreme possible case that finally in the lower momentary phase 
the momentary process should take place alone without any storing of electrons. 
In no single band, however, has this been since realised, and therefore on the 
contrary the storing of electrons has been chosen in “1909” as the characteristic 
of the lower momentary phase. 
s ) By this expression we always mean parts of the centrum itself ; it has 
already been shown in “1904” (p. 671) that the material which surrounds the 
centra has nothing to do with the retaining of the charge; cf. also “1909”, pp. 14 
et seq., and § 7 of this communication. 
