650 LOWELL—MARS ON GLACIAL EPOCHS. [Nov. 16, 
From this we see that the maxima and minima on the earth are 
as five to one; while on Mars they are as 130 to one. The ratio 
of decrease due to summer melting is then twenty-six times as great 
in the latter case as in the former. 
To the belief that Mars lacks warmth this comparison is calcu- 
lated to give a shock of surprise. But however that be, we come 
next to an even more unexpected result. 
13. This next feature is the difference in behavior of the two 
caps. At its greatest the southern cap surpasses the northern one ; 
at its least it falls below it, passing it the other way. 
It is both bigger in winter and smaller in summer than its north- 
ern counterpart. It thus outdoes its fellow in action generally— 
in accumulation first, in dissipation afterward. Beer and Madler 
stated this long ago, though curiously enough upon quite erroneous 
data. Surprising as the circumstance is—for it becomes more sur- 
prising on consideration—I think it can be shown to be the fact. 
In the case of the maxima direct data on the point are lacking. 
The maxima are not easy to determine, owing to the tilt of the axis 
and the fact that the solstices occur nearly at the apsides, and they 
never have been determined. We have, with two exceptions, only 
determinations made a long way one side or the other of the date 
of the maximum. One of these exceptions was that of Sir William 
Herschel, made six months before its summer solstice, and therefore 
about 145 days after its winter one. In 1781 he estimated the 
diameter of the southern cap at 60°. | 
In 1798 Schroeter made it 50° four months before the summer 
solstice. While Madler in 1837, at the time of the winter solstice, 
estimated it at 70°. It is quite possible that he mistook some of 
the southern islands for the cap, a mistake made by more than one 
observer. No further approach to a maximum is recorded till 
Schiaparelli observed that of 1882, 150 days before the summer 
solstice, at 45°. All of these were too far away from the true time 
of the maximum to give even approximations of it. 
The second exception was the determination made at Flagstaff in 
1846-97 on the north pole, of which a transcript follows. The 
extent of the cap has been got by taking its width from the figure 
(Annals Lowell Observatory, Vol. ii, page 232) between two given 
dates ; and the number of days before the solstice has been put as 
the mean of these two dates. 
