424 H. Draper— Photographing the Spectra. 
the spectrum increases as you pass from G toward H and above 
H, by diminishing the width of the spectrum you can in some 
measure neutralize the effect, and at one exposure obtain a 
photograph of nearly uniform intensity from end to end, 
though it is of variable width. If it were not for this it would 
be necessary to have the spectrum over-exposed at G in order 
to be visible above H, or else to resort to an elaborate dia- 
But on the other hand, the spectra of Vega and 4 Aquile 
are totally different, and it is not easy without prolonged study 
and the assistance of laboratory experiments to interpret the 
results, and even then it will be necessary to speak with fi 
essary to photograph the spectrum above H, 18 
In the case of the spectrum of Vega when examined by the 
eye, the lines C, F, near G and A, are readily visible, ts lines 
f these corresponds in position and characte® 
and seems to coincide with a iehous line. It appears 
ust as conspicuou the hydrogen lines, are 
picuous as the hydrog' mer 
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