1900.] LOWELL—MARS ON GLACIAL EPOCHS. 651 
Days after Days before 
Width of Cap. _ winter solstice. summer solstice. 
‘Jan. 11-Jan. 25 50° Jan. 48 
i= 28-47 55 
31-Feb. 10 60 Feb, 78 
Rebs G6 17. 72 6“ 90 
Tome 2 Te 70 ‘ 100 260 
(Mar. 22-Mar. 30 77 Mar. 174) 
Pga9 31 73 177 183 
26-Apr. 4 72 fs 182 178 
29- 7 OQ mae ADIs 188 172 
Apia. I= ir 63 “ 197 163 
I3z— “ 20 58 Ks 218 142 
16- * 26 49 «“ 230 130 
24-May 2 51 oe 245 114 
May 26-June 4 22 43 
28-— << 6 18 39 
It will be seen from this that we have but two determinations at 
all to the point—those of 1781 and 1897—and neither of these as 
definite as is desirable. 
That the maxima apparently occur about one hundred days after 
the winter solstices of their respective hemispheres we can gather 
from the observed times of the minima, of which we know very 
much more. But we can only surmise this, subject to future 
correction. 
Although the direct data are thus inconclusive on the subject of 
relative size, there are, however, what we may call indirect data in 
the case. If we compare the two caps at corresponding periods 
before the time of solstice we shall get a fair idea of their state mid- 
way in their career. And for this comparison we do possess very 
respectable data, since at this stage both caps have been fairly often 
and fairly well observed. ‘Tabulating all the records from ninety- 
two days before to thirty days before their respective summer sol- 
stices for the two caps, we have the following list : 
| PROC. AMER. PHILOS. soc. xxx1x. 164. QQ. PRINTED JAN. 19, 1901. 
. 
