THE 
GEOLOGICAL MAGAZINE. 
NEW SERIES. DECADE II. VOL. IV. 
No. III.— MARCH, 1877. 
>< 
OIR.IGOCIDsr-.AXj AHTICLES. 
I. EviDENCE AfFORDED BY THE PLANET Mars ON THE SüBJECT 
of Glaciab Pebiods. 
By Edward Carpenter, M.A., late Fellow of Trinity Hall, Cambridge. 
H AYING read with much interest Mr. Murphy’s papers in the 
Journal of the Geological Society for 1869 (p. 350) and for 
1876 (p. 400), in which he maintains that at the time of inaximum 
excentricity of the Earth’s orbit that hemisphere would be glaciated 
which had its winter in aphelion, as against Mr. Croll, whose tlieory 
is that the glaciated hemisphere would be that which had its summer 
in aphelion : it has occurred to me that 1 have never seen, in this 
discussion, any reference to the case of the planet Mars. 
It may be worth while, therefore, in case no one has done so 
before, to point out how remarkable a parallel may be drawn 
between the state of affairs on that planet and on the earth, and how 
remarkable a confirmation the relative dimensions of the snow-caps 
on that planet appear to give of Mr. Murphy’s view of the matter. 
The excentricity of the orbit of the planet Mars is, as is well 
known, considerably greater than that of the earth’s orbit. It is 
given by Sir John Herschel, in his Outlines of Astronomy. as 
(J-0931125. Leverrier’s estimate of the maximum excentricity of the 
earth’s orbit, as quoted by Mr. Croll, is 0-07075. The excentricity 
of Mars’ orbit is therefore somewhat greater than the maximum 
excentricity of that of the earth. Again, the inclination of the axis 
of Mars to the perpendicular to the plane of its orbit is 28° 51', 
which in a similar way is somewhat greater than the inclination of 
the earth’s axis to the plane of the ecliptic, which is 23° 27' 24". So 
that in both respects Mars offers a slight exaggeration of the 
conditions supposed to prevail in the case of the earth at the time 
under consideration. But these coincidences would be of no Service 
to us, were they not supplemented by a third, most fortuuate, 
coincidence. The axis of Mars, namely, is inclined at the present 
time towards one extremity of the axis of its orbit, and indeed 
towards the perihelion point ; so that as on the earth at the present 
time the winter solstice of the Northern hemisphere coincides with 
perihelion, its summer solstice with aphelion, and the winter solstice 
of the Southern hemisphere coincides with aphelion, the summer 
solstice with perihelion. To show how nearly this is the case it 
will be sufficient to quote the lengths of the seasons. They are 
given as follows (from elements of the planet obtained by Maedler 
DECADE II. — VOL. IV. — NO. UI 7 
