H. Draper— Oxygen in the Sun. 275 
Mr. Christie: I should not have risen except that reference 
had been made to my remarks. I do not know that I should 
say very much, but I think I may remark with reference to 
this question of coincidence, that everything turns upon the 
exactness of the coincidence, and whether these are actually 
coincidences or not. am not quite prepared to admit that 
these coincidences are perfect; in fact, I should say there are 
even coincidences of dark lines with some of the oxygen lines. 
I admit that it is a matter of judgment, and I should be sorr 
to say positively that there are such coincidences with dar 
lines. But there is considerable uncertainty in the matter. As 
Dr. Draper has explained there is a great difficulty in establish- 
ing coincidences, and you have to adjust your apparatus until 
you match coincidences by the known lines of iron. It seems 
some of these do not coincide exactly with the dark lines in the 
sun. I only alluded to that as being one of the difficulties we 
have to contend with. With regard to Mr. Ranyard’s remarks 
as to the eye perceiving differences of brightness which the 
photographs do not show, I would merely wish to ask whether 
e has examined with his eye different parts of the spectrum, 
for there is a certain part in the neighborhood of the G lines 
which I have examined and find the photograph gives grr y 
spectrum of hydrogen and the air spark spectrum at ordinary 
pressures, The cuba spectrum of dedesgen showed four hy- 
drogen lines perfect throughout, but only one of these lines was 
represented in the spectrum of air at ordinary pressure, so that 
It is possible certain oxygen lines present in the sun may be 
absent in the spark spectrum. 
Dr. Draper : I have taken the oxygen spectrum under a great 
many different circumstances. n with tubes containing 
oxygen and compounds of oxygen, but the difficluty is that you 
are limited to rather small dispersion, because you cannot get 
