BY CLEAVAGE, ETC. 31 
observed. The rare mineral called samarskite (nio- 
bate of iron, of uranium, and of yttria) presents the 
same phenomenon to a less degree. 
Oxide of molybdenum (MoO) is obtamed by 
heating the hydrate of this oxide in vacuo: 
when the water is all evaporated, the dry oxide re- 
maining appears as if on fire; the anhydrous or 
dry oxide is then completely formed. 
According to Berzelius antimoniate of copper 
becomes luminous when heated, and changes its 
chemical nature. Something similar has been ob- 
served with phosphate of magnesia. 
About fifteen years ago, M. Scheerer showed 
that the density of gadolinite (which, like samar- 
skite, contains no water) increases during the 
phosphoric radiation ; the density of the mineral is 
ereater after the experiment than before. M. H. 
Rose has confirmed this fact anew, and has shown 
at the same time, that with samarskite the con- 
trary is observed: the density diminishes. These 
observations alone prove that a molecular change 
takes place during the emission of light. 
H. Rose has also confirmed the fact announced 
some time ago by Regnault as an hypothesis, viz. 
that the lumimous phenomenon which occurs 
when the substances above alluded to suddenly 
change their state, is accompanied by an imme- 
diate change in their specific heat. Thus, the 
specific heat of gadolinite diminishes one-four- 
