176 J. W. Draper—Phosphorograph of a Solar Spectrum. 
V. Or tue Extincrion oF PuaosPpHoRESCENCE BY Rep LIGHT. 
I turn now to an examination of those parts of the phospho- 
rographic spectrum from which the light has been removed. 
They are from the line F to the end of the infra-red space, 
.and again for a short distance above the violet. The effect 
resembles the protecting action in the same region of a photo- 
raph. 
q Now if similar effects are to be attributed to similar causes, 
we should expect to find in the photograph and phosphoro- 
graph the manifestation of a common action. 
Several different explanations of the facts have been offered. 
Herschel suggested that the photograph might be interpreted 
on the optical principle of the colors of thin films. Very re- 
cently Captain Abney has attributed the appearance of the 
lower space to oxidation. But this can scarcely be the case in 
all instances. Mr. Claudet showed, in a very interesting paper 
on the action of red light, that a daguerreotype plate can be 
used again and again by the aid of a red glass, and that the 
sensitive film undergoes no chemical change. (Phil. Mag., 
February, 1848.) ; 
It was known to the earliest experimenters on the subject 
that if the temperature of a phosphorescent surface be raised, — 
the liberation of its light is hastened, and it more quickly 
relapses into the dark condition. he memoir to which I 
I speak of this as ‘the old view,” because, as I have en 
where shown, the curves supposed to represent heat, cago 
surface on which the ray falls. (Phil. Mag., August, 1872, 
December, 1872. 
But this heat explanation of the phosphorescent facts can 
not be applied to the photographic. Nothing in the a 
hastened or secondary radiation seems to take place in thé 
case. 
In phosphorescence the facts observed in the production . 
this blackness are these. If a shining phosphorescent surfac 
