50 
POPULAR SCIENCE REVIEW. 
the spectrum. But the faintness of this part of the spectrum 
(lid not permit him to determine whether these lines are the 
same as those which occur in the same part of the solar spectrum, 
or whether any of them are new lines due to absorption under- 
gone by the light at reflection from the planet. 
He also detected (as in former observations) several strong 
lines in the red part of the spectrum, and it is to these that the 
chief interest of bis paper attaches. He saw Phaunhofer’s c 
very distinctly, and another line about one-fourth of the way 
from c tow’ards b. As the latter line has no counterpart in 
the solar spectrum it was clearly due to an absorptive effect 
produced by the planet’s atmosphere. On February 14, Mr. 
Huggins was able to detect faint lines on both sides of Fraun- 
hofer’s D. These lines occupied positions in the spectrum ap- 
parently coincident with groups of lines which make their 
appearance in the solar spectrum when the sun is low down, so 
that its light has to traverse the denser strata of the atmosphere. 
It remained however to show that these lines were produced by 
the atmosphere of Mars and not by that of our own earth. 
This Mr. H uggins efiected in the following manner: — The 
moon w’as, at the hour of observation, somewhat loww down than 
Mars, so that if the lines were due to the absorptive effects of 
our atmosphere, they should have been more distinctly marked 
in the spectrum of the lunar light than in that of the light from 
Mars. But when the spectroscope was directed to the moon 
these lines were not visible, thus conclusively proving that the 
lines were caused by the absorptive action of the Martial atmo- 
sphere. ^Ir. Huggins noticed in confirmation of this that the 
lines seemed more distinct in the light from the margin of the 
disc, but he was not quite certain on this point. 
This observation proves the presence of aqueous vapour 
in the atmosphere of Mars, since the lines in question have 
been showm to be caused, in the case of our atmosphere, by the 
vapour of water. 
From the spectroscopic analysis of the darker portions of the 
disc of ^lars, Mr. Huggins Wiis led to the conclusion that these 
pirts are neutral or nearly so in colour. 
Jle considers also that the ruddy colour of Mars is not due to 
the eftecta of the planet’s atmosphere. Indeed, this seems 
almost obvious when we consider that the polar spots look 
perfectly white, or at least show not the slightest tinge of 
red, tliough, being situated upon the edge of the disc, they 
should exhibit the effects of the atmosphere’s absorptive powers 
on the rays from the blue end of the spectrum, more strongly 
than the central parts of the disc, where the light has passed 
throtigh a much smaller range of atmosphere. Clearly w’e may 
look upon the red colour of parts of Mars as due to the nature 
of the planet’s soil. 
