39 § 
Spontaneously Reversible Spectral Rays. 
[July, 
IV. ON THE SPONTANEOUSLY REVERSIBLE 
SPECTRAL RAYS, 
AND ON THE 
ANALOGY BETWEEN THEIR LAWS 
OF DISTRIBUTION AND INTENSITY, WITH 
THOSE OF THE RAYS OF HYDROGEN. 
(Concluded from page 352.) 
Particular Arrangement of the Spontaneously Reversible 
Groups. 
HEN we examine, in different photographic proofs, 
the groups of rays which are reproduced periodic- 
ally with an especial regularity, we find most fre- 
quently that these groups belong precisely to the category 
of the spontaneously reversible rays, for some of them are 
reversed and the others are on the point of being so : for 
one and the same metal the reversals are more or less com- 
plete according to the conditions of the experiment, and for 
different metals according to the chemical and physical 
properties of the metal. Further, the law of the distribu- 
tion of these groups presents another character common 
relatively to the succession of distances and of intensities : 
the rays become more and more close together towards the 
more refrangible side, decreasing at the same time in in- 
tensity. This feature is the more striking as the number of 
reversed rays is more considerable, and as the field upon 
which they are detached is more uniform. It seems as if, 
with the rise of temperature, the spedtrum tends towards a 
final aspedt, — that of a continuous brilliant ground, devoid 
of every ray other than the regular series of the sponta- 
neously reversible rays. It is to this constitution, which is 
to some extent ultimate, that M. Cornu wishes to draw the 
attention of observers. 
The number of metallic spedtra which can give a regular 
series of spontaneously reversible rays is very considerable ; 
but the first series hitherto observed are furnished by two 
metals which, from a chemical point of view, we should not 
