104 Scientific Intelligence. 
degree of distinctness and purity. It exhibits in the solar spectrum 4 i 
thousands of lines with such clearness that they are easily distinguished — 
which lies between Fraunhofer’s lines D an 
This apparatus exhibits the spectrum of an artificial source of light with 
the same distinctness as the solar spectrum, provided only that the inte 
sity of the light is sufficient. A common gas flame in which a metalli¢ — 
compound evaporates, is usually not sufficiently luminous but an electn¢ — 
es with the ; 
a 
i 
: 
as easily as that of ’ 
A very simple arrangement permits the comparison of the spectra of 
two sources of light. The rays of one of the sources may pass through — 
the upper half of the vertical slit, while those of another pass through — 
_the lower half. When this is the case, one of the two spectra is seed 
immediately beneath the other, and it is easy to determine whether coin 
both : 
i . . ? . 
marked lines occur, resulting from the iron in the sun’s atmosphere. 
Tron is remarkable on account of the great number of distinct lin’ 
in their — but no distinct dark lines in the solar spectrum corres: 
; ese, ‘ 
Many metallic compounds do not give in a gas flame the tram of 
their metal, because a 4 é gerry 
of which the spectrum of every electric spark consists, it is n 
have recourse to a particular arrangement. The electric spark 
allowed to pass at the same time between two similar pairs of ¢ 
