all 
Physics and Chemistry. 107 
upon the temperature and density of the ignited gas. Setting out 
with these principles, the author arrives at the following law: 
more rapidly than so The author in the next place shows that 
in the case of dark bands in a spectrum, produced by inversion, 
the distribution of the darkness, so to speak, and the breadths of 
the band will follow the same law as that above given for bright 
bands. e mere comparison of the relative breadths .of the 
bands may lead to important conclusions. If in any gas-spectrum 
bands of different breadths lie near together, we might infer the 
presence of a mixture of gases of different densities, or of differ- 
ent allotropic states of the same gas. ‘Thus the author thinks that 
the same molecules, or ditions. 
same gas the breadth of the spectral bands permits a conclusion 
as to the temperature. is is of special interest in the case of 
ases and 
e umbra must have a higher temperature than 
i ich Fraunhofer’s 
