554 E. BECQUEREL ON TIE CONSTITUTION 
the sulphuret of barium (Bologna phosphorus). By preparing 
a paper with the powder of this substance, and placing it as the’ 
preceding one in the spectrum, we soon see the part a 8, fig. 12, 
become luminous ; but there is only one maximum, situated be- 
tween the lines I and M; the limits of this spectrum of phos- 
phorogenic rays are towards G on one part, and on the other 
towards P. 
Moreover, if the whole surface is affected before the experi- 
ment, and it is then subjected to the action of the spectrum, we 
observe, as in the case of the sulphuret of calcium, that there is 
a space which becomes luminous from yw as far as », fig. 12. This 
part therefore contains rays which destroy the phosphorescence ; 
they extend nearly as far as those which act on the sulphuret of 
calcium, and their effects are the same on these two sulphurets. 
I wished to see if, in the spectra of the rays which act on phos- 
phorescent bodies, there were lines as in the luminous and che- 
mical spectra. In order to ascertain this, we are obliged to en- 
large the spectrum by projection. That which had been before 
employed was half the size of those which are represented in the 
plates* ; but when a spectrum of this size is employed, we cannot 
distinguish the lines on phosphorescent substances. Is this effect 
caused by the phosphorescence being propagated from molecule 
to molecule, as an experiment made by M. Biot and my father 
seems to show? Ido not at all know. Whatever may be the 
cause, it is necessary to increase the spectrum. I augmented it 
ten times in length, or at least each part of the spectrum sepa- 
rately. This is easy to effect: instead of receiving the spectrum — 
by projection at the focus of the great lens on a surface covered — 
with a phosphorescent matter, we place in the path of the rays 
a lens having a focus of not more than one decimetre, in such a 
manner that the focus of the great lens falls between the focus 
and the surface of the second; then, somewhere on the other 
side of the latter, we have an enlarged spectrum; by moving the 
second lens in all the parts of the primitive spectrum, then seek- 
ing the place of the image by projection with a white card, we 
have a spectrum in which the lines are broad and very distinct ; 
by receiving it on the surface covered with phosphorescent mat- 
ter, we again find the same lines as in the luminous and che- 
mical spectra. 
In order to study them with advantage, we receive the spec- 
[* N.B. The Plate which accompanies this translation is reduced to one- 
half the size of that in the original—Ep.] 
