﻿98 Edivard Carpenter — The Planet Mars. 



and Sir William Herscliel) by Mr. Breen, of the Cambridge Obser- 

 vatory. For the Northern hemisphere : — 



Spring (vernal equinox to summer solstice)... 191^ Mars' Days. 



Summer 181 „ „ 



Harvest 149^ „ ,, 



Winter 147 „ „ 



Thus we have on Mars at the present time all the conditions 

 prevailing which the case under consideration requires — only ex- 

 aggerated : the axial inclination is slightly greater, the excentricity 

 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 thi'oughout, 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, unfortunately, able at the 

 present moment to lay my hand on the latest investigations into this 

 subject ; but I 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 perhaps they are not far from 

 equal. But there is a marked difference between their fluctuations : 

 the Northern cap in fact changes slowly and little, the Southern 

 fluctuates rapidly and much. The following facts will give an idea 

 of their range and variation. In the year 1830 a favourable oppor- 

 tunity occurred for viewing the Southei'n 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' 



July 7 



Diameter of spot 6° 20' 



23 



11° 30' 



9 



„ 5° 46' 



26 



7° 10' 



19 



„ 8= 2' 



Thus at a time of year corresponding to our July 9 the snow-cap 

 fell to a minimum, and was only 5° 46' broad. It will be seen, too, 

 that it fell off rapidly, having been more than twice as broad a 

 month 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, although 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- 



