552 E. BECQUEREL ON THE CONSTITUTION 
the phosphorogenic spectrum, there were lines, as in the luminous 
spectrum and the chemical spectrum. a 
I have been led to an affirmative conclusion, that is to say, that 
the lines are absolutely the same in the spectra arising from these 
three radiations, at least taking into consideration only the parts 
of like refrangibility ; but in making these experiments I have 
discovered new rays, of which I shall speak before describing the 
lines of the phosphorogenic radiation. We begin by reducing 
to powder the sulphuret which is to be used, for example the 
sulphuret of calcium ; a layer of gum-arabic is put upon a sheet 
of paper stretched in a wooden frame, and this paper is powdered 
with the sulphuret; when it is dry we have a surface equally 
phosphorescent in every part. The paper thus prepared is placed 
at the focus of the lens which gives by projection the solar spec- 
trum with all its lines. Let us for the moment leave the lines 
out of consideration; if, whilst the surface which is done over 
with the sulphuret of calcium receives the action of the spectrum, 
we keep our eyes shut, and then, having closed the aperture of 
the shutter, we look upon the surface, two luminous bands are 
visible, « 6, y 2, fig. 11. Pl. IX., separated by an interval which 
is not much illuminated. The part of the spectrum which gives 
the phosphorescence to the sulphuret of calcium, extends there- 
fore from G to Z, beyond P. There are two maxima of action, 
one between G and H, but nearer to H, and the other at O. 
In the upper part of fig. 11, which represents this effect, the 
light portions are white, and those which are dark are black. 
We see that they are as it were two phosphorogenic spectra. 
But this is not all; if we let the action continue during a certain 
time, a quarter of an hour for example, the diffused light which 
accompanies the spectrum impresses the remainder of the surface 
almost everywhere, so that by closing the aperture of the shutter 
again, we see nearly the whole surface luminous, the parts a 8, y 8 
being most bright; but what is remarkable, is that the space 
from the line G to beyond A is completely dark. The lower 
part of fig. 11 represents the effect produced. This experiment 
seems to show the existence of rays in this part of the spectrum 
which act in an opposite manner to the phosphorogenic rays, 
that is to say which destroy the phosphorescence. I have suc- 
ceeded in placing this fact beyond doubt by means of the two 
following experiments :— 
Before exposing the phosphorescent surface to the action of 
