98 
Edward Carpenter — The Planet Mars. 
and Sir William Herschel) by Mr. Breen, of the Cambridge Obser- 
vatory. For the Northern hemisphere : — 
Spring (vernal equinox to summer solstice)... 191 J Mars’ Days. 
Summer 181 „ „ 
Harvest 149J „ ,, 
Winter 147 „ „ 
Thns we have on Mars at the present time all the conditions 
prevailing which the case linder consideration requires — only ex- 
aggerated : the axial inclination is slightly greater, the exceutricity 
is greater, and the year is longer, 687 of our days instead of 365. 
Yet the exaggeration, at any rate in the cases of the axial inclina- 
tion and excentricity, is by no means so great as to destroy the 
comparison : on the contrary, it might be expected just to emphasize 
it. One more point before proceeding to actual observations of the 
polar snows of Mars ; the distribution of land and sea on that planet 
is far more equable than on the earth, indeed there is a remarkable 
symmetry or likeness between the two hemispheres ; at neither pole 
is there, apparently, an ocean of great extent, and, as is well known, 
land predominates largely over sea throughout, the two being in an 
estimated proportion of three or four to one. Thus, as far as we 
can at all judge, geographical causes of difference between the poles 
seem to be next to eliminated on Mars, and we are left to observe 
the results of the purely astronomical influences. 
And they are remarkable. I am not, unfortuuately, able at the 
present moment to lay my liand on the latest investigations into this 
subject ; but 1 hope that the present paper may be the means of 
drawing more information from others. However, the main facts 
are clear enough. There is no great disproportion between the 
snow-caps of Mars ; on the whole perbaps tliey are not far from 
equal. But there is a marked ditference between their fluctuations : 
the Northern cap in fact changes slowly and little, the Southern 
fluctuates rapidly and rauch. The following facts will give an idea 
of their ränge and Variation. In the year 1830 a favourable oppor- 
tunity occurred for viewing the Southern cap ; it was during the 
summer-time of that Pole, and the following measurements were 
taken, the times of year corresponding to our summer months being 
given (Breen’s Planetary Worlds, p. 177) : — 
June 16 Diameter of spot 12° 46' 
23 „ „ 11° 30' 
26 „ „ 7° 10' 
July 7 
9 
19 
Diameter of spot 
)> >> 
>> >» 
6 ° 20 ' 
5° 46' 
8 ° 2 ' 
Thus at a time of year corresponding to our J uly 9 the snow-cap 
feil to a minimum, and was only 5° 46' broad. It will be seen, too, 
that it feil off rapidly, having been more than twice as broad a 
montli before. This would lead us to expect a large extent in 
winter-time : and we find that at the Opposition of 1837 a good part 
of the Southern snow-cap was seen, althougli the South Pole was 
then turned away from the earth (and of course from the sun too) ; 
in fact it was estimated that it extended to a distance of 35° from 
the Pole, though this seems to have been an exceptional occasion. 
In the year 1837 similar measurements were taken of the mini- 
