Vol. 6, 1920 PHYSICS: NICHOLS AND WILBUR 693 
LUMINESCENCE AT HIGH TEMPERATURES 
By K. L. Nichols and D. T. Wilbur 
Physical Laboratory, Cornell University 
Read before the Academy, November 20, 1920 
It is the purpose of this note to announce the discovery of luminescence 
at temperatures above those at which ordinary phosphorescence disap- 
pears and fluorescence, excited by hght, reaches extinction: in a v\^ord, 
roughly speaking, above the beginnings of a visible red heat. 
Luminescence at these higher temperatures has probably remained un- 
noticed^ because the usual source of excitation has been light and photo- 
excitation, as was observed by Lenard and Klatt^ in their studies of the 
phosphorescent sulphides, generally ceases below 400° C. The experi- 
ments of Wiedemann and Schmidt^ on the effect of temperature on the 
kathodo-luminescence of certain substances reached their upper limit 
at about the same temperature, not because the materials ceased to glow 
but on account of the softening of the glass of their vacuum tubes. 
The main facts about this luminescence at high temperatures, the de- 
tails concerning which will be given in a series of forthcoming papers, 
may be briefly stated as follows: 
1. The glow is produced by a new type of excitation, i. e., by contact with 
the outer zone of the hydrogen flame; also in some instances by kathode 
bombardment and the action of X-rays. 
2. The ejffect is quite distinct from photo-luminescence, from which it 
differs in the following respects: 
(a) It is observable in many substances incapable of excitation by 
light; such as the oxides of calcium, zinc, magnesium, aluminum, silicon 
and zirconium; and in sulphides of calcium and zinc of such purity as to 
be non-phosphorescent. 
{b) It is absent in some strongly fluorescent materials such as willemite 
and calcium tungstate. 
(c) The addition of a trace of some activating substance, as in the pro- 
duction of the phosphorescent sulphides, is not necessary. Such an admix- 
ture sometimes modifies the color of the glow but more frequently pre- 
vents fluorescence altogether. Thus many of the lycnard and Klatt 
sulphides and the well-known, red glowing, cadmium phosphate of Andrews 
are inert under the excitation of the flame. 
(d) Where photo-fluorescent substances are active, as in Sidot blende, 
Balmain's paint and several of the phosphorescent sulphides, the lumi- 
nescence has an upper limit of temperature far above that at which photo- 
excitation ceases. 
3. Distinguishing features in relation to temperature radiation. — The ef- 
fect often occurs at temperatures far below the red heat. When super- 
imposed upon the red heat it is readily distinguishable: 
