90 H. Draper—Discovery of Oxygen in the Sun. 
In support of the above assertions the accompanying photo- 
graph of the solar spectrum with a comparison spectrum of alr, 
and also with some of the lines of iron and aluminium, is intro- 
du he photograph itself is absolutely free from hand- 
work or retouching. It is difficult to bring out in a single 
photograph the best points of these various substances, and I 
ave therefore selected from the collection of original negatives 
that one which shows the oxygen coincidences most plainly. 
There are so many variables among the conditions which con- 
spire for the production of a spectrum, that many photographs 
must be taken to exhaust the best combinations. The pressure 
of the gas, the strength of the original current, the number of 
Leyden jars, the separation and nature of the terminals, the 
nm 
ao 
= 
et 
ro 
° 
"A 
Sef 
9°) 
=] 
o 
Pa) 
i=] 
ct 
oa 
ro) 
me 
Lee § 
° 
— 
“ih 
=} 
B 
5 
oy 
o 
o 
=i 
creased in number and distinctness. For the metals the electric 
are gives the best photographic results as Lockyer has so well 
shown, but as my object was only to prove by the iron lines 
that the spectra had not shifted laterally past one another, those 
that are here shown at 4825, 4807, 4971, 4063, 4045, suffice. 
In the original collodion negative many more can be seen. 
' Below the lower spectrum are the symbols for oxygen, nitrogen, 
iron and aluminium. 
No close observation is needed to demonstrate to even the 
