H. Draper—Discovery of Oxygen in the Sun. 93 
are only partly accounted for by oxygen. Further investiga- 
tion in the direction I have thus far pursued will lead to the 
discovery of other elements in the sun, but it is not proper to 
conceal the principle on which such researches are to be con- 
ducted for the sake of. personal advantage. It is also probable 
that this research may furnish the key to the enigma of the D, 
or helium line and the 1474 K or corona line. The case of the 
D, line strengthens the argument in favor of the apparent ex- 
emption of certain substances from the common law of the 
relation of emission and absorption, for while there can be no 
doubt of the existence of an ignited gas in the chromosphere 
giving this line, there is no corresponding dark line in the 
. 
or channelled spectra. This subject requires careful investiga- 
tion. The diffused and reflected light of the outer corona 
could be caused by such bodies cooled below the self-luminous 
nt. 
wo Ww : 
machine thoroughly adjusted, a large Ruhmkorff coil with its 
Foucault break in the best order, a battery of Leyden Jars 
carefully proportioned to the Plticker’s tube in use, @ heliostat 
Which of course involves clear sunshine, an optical train of 
slit, prisms, lenses and camera well focussed, and in addition 
to all this a photographic laboratory in such complete condition 
that wet sensitive plates can be prepared, which will bear an 
exposure of fifteen minutes and a prolonged development. ‘It 
has been difficult to keep the Pliicker’s tubes in order; often 
before the first exposure of a tube was over the tube was 
Tuned by the strong Leyden sparks. Moreover to procure 
tubes of known contents is troublesome, For example, my 
