OXYGEN AND WATER ON MARS 
others the polar atmosphere. The polar 
snow-cap was then in process of melting 
and the plates showed that the band 
in the Martian spectrum, denoting 
water-vapor, had been intensified sev- 
enty per cent in the planet’s polar regions 
and but sixteen per cent in the equa- 
torial over what the band showed in 
our own. Furthermore, Professor Very 
remarks about one of the polar plates 
“there is a brighter streak of continu- 
ous spectrum, corresponding to a region 
of melting snow or of clouds, which gives 
a larger intensification of a (the water- 
vapor band) than the associated dark 
streak, when these are measured sepa- 
rately. The diversity of intensification 
appertains to a_ exclusively —a_ has 
changed by nearly fifty per cent and this 
change is certainly Martian.”’ He con- 
cludes by saying with regard to oxygen 
that with the higher altitude of Mars in 
209 
the later results, the oxygen interposed 
by the earth’s atmosphere being less by 
one-half an atmosphere, he found the 
fifteen per cent due to Mars in his earlier 
measures increased to twenty-four per 
cent in his later ones, “proving again 
that this apparent intensification is also 
real, and is truly Martian, and indicat- 
ing that the actual amount of oxygen 
in the Martian atmosphere is about half 
as great as upon the earth.” ~ 
Surprising as have been the disclosures 
due to spectroscopy, perhaps none is 
greater than that that instrument should 
inform us of the possibility of life upon 
another world, a_ possibility, which, 
combined with facts that visual observa- 
tion has revealed (size, mass, tempera- 
ture and lastly details of the canal-oasis 
system), amounts, viewed in the light of 
the doctrine of probabilities, to practical 
certainty of its existence there. 
Mars 
Moon 
che, Ree? 
Moon 
is 4 D Ca BY een 
Photo by Dr. V. M. Slipher 
Spectra of Mars and the moon. The band marked a, well on the right of the spectra, is the 
band of water-vapor. In the case of the moon the light has traveled only through our own atmosphere, 
and in that of Mars through the Martian and our own. The difference in darkness shows that water- 
vapor exists in the atmosphere of Mars. This spectrogram shows also that oxygen exists on Mars, by 
comparing the line B, oxygen, with C, hydrogen, in the sun for relative intensities. Its presence was 
found by very careful measurements by Professor Very with his devised comparator, at the time he 
evaluated the amount of water-vapor in the Martian air 
