1900.1, LOWELL—MARS ON GLACIAL EPOCIIS. 641 
MARS ON GLACIAL EPOCHS. 
BY PERCiVAL LOWELL. 
(Read November 16, 1900.) 
1. Croll’s ingenious theory that eccentricity of orbit combined 
with axial tilt produced our glacial periods challenges comparison 
outside the earth. And an example lies ready to its hand, in the 
planet Mars. For Mars not only presents appearances singularly 
suggestive of our polar snows, but stands so conditioned in eccen- 
tricity and tilt as to promise a criterion of a crucial character. 
In consequence such appeal was very soon made and with the 
result of a seemingly complete denial. Although admirably cir- 
cumstanced to exemplify the theory Mars did nothing of the sort. 
No marked preponderance of snow distinguished the hemisphere 
which glaciation should have covered. The ill-conditioned one 
showed as conclusive a snow-sheet as its fellow. Eccentricity 
apparently was powerless to effect vitally deposition about the pole. 
This was more than a quarter of a century ago, and the last quar- 
ter of a century has revolutionized our ideas of the physical condi- 
tion of Mars. Especially in the matter of water, we now have 
knowledge which has particular bearing upon the subject. We no 
longer believe Mars to be acounterpart of the earth. Among 
much that is analogous we see much that is the reverse ; and with 
the flight of the similar the cogency of the argument departs. In 
the light of this change it becomes advisable to reopen the case ; 
and I therefore make bold to introduce it to the notice of the 
Society. 
2. Round about those parts of Mars which the motion of the 
markings point to as the planet’s poles may be seen two roughly 
circular white patches, sharply contrasted with the other features of 
the disk.. Each is fairly regular in shape, but changes in size ac- 
cording to what more particular inquiry shows to be the changing 
seasons of the planet’s year. When the one patch is large the 
other is small ; and as the one waxes the other wanes, the mass of 
white shifting from pole to pole with a certain chronometic cadence. 
Both appearances and behavior commended them to Sir William 
Herschel for polar snows, and such they have generally been con- 
sidered since. Indeed the more minute our study of them, the 
more they seem to justify the imputation. 
