of the Solar Atmosphere. 187 
ment it is extremely easy to see whether any coincident lines 
occur in the two spectra. 
“T have in this way assured myself that all the ios lines 
characteristic of iron correspond to dark lines in the solar spec- 
trum. In that portion of the solar spectrum which I have ex- 
amined (between the lines D and F), I have had occasion to 
remark about seventy particularly brillant lines as caused by the 
presence of iron in the solar atmosphere. Angstrém only ob- 
served three bright lines in this part of the spectrum of the 
electric spark ; Masson noticed only a few more; Van der Wil- 
ligen says that iron produces only a very few feeble lines in the 
spectrum of the electric spark. From the number of these lines 
which I have been able to observe with ease, and map with abso- 
lute certainty, some idea may be formed of the capabilities of the 
instrument which I am fortunate enough to possess. 
“ Tron is remarkable on account of the number of the lines 
which it causes in the solar spectrum; magnesium is interesting - 
because it produces the group of Fraunhofer’s lines which are 
most readily seen in the sun’s spectrum, namely, the group in 
the green, consisting of three very intense lines to which Fraun- 
hofer gave the name 6. Less striking, but still quite distinctly 
visible, are the dark solar lines coincident with the bright lines 
of chromium and nickel. The occurrence of these substances in 
the sun may therefore be regarded as certain. Many metals, 
however, appear to be absent; for although silver, copper, zinc, 
aluminium, cobalt, and antimony possess very characteristic 
spectra, still these do not coincide with any (or at least with any 
distinct) dark lines of the solar spectrum. I hope before long 
to be in a position to publish more extended information on this 
oint. 
Me The combination of Ruhmkorff’s induction coil with the spec- 
trum apparatus will doubtless also be of importance for the che- 
mistry of terrestrial matter. Very many metallic compounds do 
not give the spectrum peculiar to the metal when placed in a 
flame, because they are not sufficiently volatile, but they give it 
at once when placed on the electrodes of an electric spark. 
These lines are then indeed seen, together with those of the 
metal of the electrode, and those of the air through which the 
spark passes; and owing to the great number of bright lines 
which compose the spectrum of every electric spark, it would be 
almost impossible, without a special arrangement, to distinguish 
the lines caused by the metal of the electrodes from those pro- 
duced by the metallic salt added. The special arrangement 
which in this case removes all difficulty, consists in allowing the 
spark to pass at the same instant between two pairs of electrodes, 
in such a manner that the light of one spark passes through the 
