THe American Museum Journal 
VoLuME XV 
MAY, 1915 
NuMBER 5 
OXYGEN AND WATER ON MARS 
By Percival Lowell 
Director of the Lowell Observatory, Flagstaff, Arizona 
EXT to the photographs of the 
canals of Mars, perhaps the most 
vitally interesting photograph 
in the recent work of the Lowell Observa- 
tory is a spectrogram of Mars by Dr. Y. 
M. Slipher, disclosing to the average ob- 
server merely a darkening of one of the 
spectral lines (a) to the red end of this 
spectrum over the same line in the col- 
lateral spectrum of the moon. But to 
scientific insight this bit of glass is other- 
wise transparent. For the slight differ- 
ence in tone between these identically 
positioned lines in the two photographs 
means all the difference between life 
and death. It reveals the fact that 
water-vapor is present in the atmos- 
phere of Mars. The moon, an almost 
absolutely airless body, delivers us the 
sun’s rays unaffectedly and the absorp- 
tion line in question in its spectrum 
is caused by water-vapor in our own air. 
Indeed the spectrum of the moon is 
simply the spectrum of the sun plus 
that of the earth, the moon acting only 
the self-effacmg part of a mirror. But 
in the Martian spectrum the sun’s rays 
have passed in addition through that 
planet’s air and in so doing reveal of 
what it stands composed. The empha- 
sis it lays upon this line indicates that 
water, without which all life, vegetal or 
animal, is impossible, exists upon our 
neighbor, even as it does here. 
Nor is this all that this spectrogram dis- 
closes. In the able hands of Professor F. 
W. Very, measurements of the intensity 
of another line (B) have revealed the 
presence of oxygen too, in that other 
world. Here then we have demonstra- 
tion that both of the chief substances 
necessary to life are present on Mars. 
This evidence was obtained several 
years ago at a most propitious time, be- 
cause at the time and place when the 
earth’s air happened to be particularly 
dry, thus permitting of accentuated 
contrast. In addition to this however, 
spectrograms taken by Dr. Slipher more 
recently, have added to it in an unlooked- 
for way. Our air, on this latter occasion, 
was unavoidably more moisture-laden 
and little was hoped for from the spec- 
trograms beyond a faint corroboration 
of previous results. When behold, not 
only did measurement of intensities dis- 
close both water-vapor and oxygen on 
Mars as before, but these intensities were 
such as fitted the changed terrestrial 
conditions, thus adding to qualitative 
proof, quantitative proof as well. And 
both fitted in with the Martian meteor- 
ology which visual study of that planet 
has shown us must exist. 
Even this is not the limit of the infor- 
mation conveyed by these communi- 
eative lines. In Dr. Slipher’s latest 
results, four plates were taken so varied 
that in two the air above the equatorial 
regions of Mars was examined, in two 
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