28 J. W. Draper—Distribution of 
in benzine, and developed by a mixture of benzine and alcohol. 
The bitumen solution being poured on a glass plate in a dark 
room, and drained off as in the operation of collodion, leaves a 
film sufficiently thin to be iridescent. This is exposed to the 
spectrum for five minutes, and then developed. 
The beginning of the impression is below the line A, its 
termination beyond H. Every ray in the spectrum acts. The 
ee is continuous except where the Fraunhofer lines fall. A 
etter illustration that the chemical action of the spectrum is 
not restricted to the higher rays, but is possessed by all, could 
hardly be adduced. 
3d.— Case of Carbonic Acid. 
. 
