27 
1 69°*37 for 10,000 years. To bring it to 60°, which is nearly 
the position of maximum effect, would require an interval of 
3,900 years, or a date from A.D. 1800 backward, of 846,100 
years. The corrected exentricity would then be about ’06476, 
instead of ’0664 or ’0747. The depression, by the corrected 
rule, at this the most favourable moment, since the logarithm of 
the radius vector at the aphelion would be ’02725, will repre- 
sent a diminished heat, compared with a circular orbit, of 
29°’58, or 2°’7 F., and this will be counteracted by a summer 
heat, exceeding the present by 24 0, 8 F., or an average of 89°. 
48. The other periods most favourable to the effect of 
depressing the northern winters will be, reckoning backward 
from A.D. 1800 as before. 
823,000 diminution from present winter heat 28 0, 4 result 10 - 6 
217,400 „ „ „ 28°’3 „ 107 
195,100 „ „ „ 29°’6 „ 9’4 
Now, when we remember that the approach to the maximum 
would last only one or two thousand years ; that the summer, 
in each case, would be hotter than at present by all the contrast 
between the present aphelion and the past perihelion distance ; 
that the heat annually received by the northern hemisphere 
at these periods is 3 or 4 per cent, above the mean amount ; 
and that the actual difference of the northern and southern 
winters, which by the same scale should be 13°’ 7, or nearly 
half the whole amount, is in reality hardly sensible, I think 
the presumptive evidence is irresistible in favour of the 
view of Sir J. Herschel, Arago, and others, which Mr. Croll 
reverses as erroneous ; that the differences of excentricity, 
within their actual limits, will by no means account for the 
occurrence of glacial periods. 
49. There is another hypothesis, wholly distinct from that 
of Mr. Croll, which seems to me to admit of being confirmed 
by very strong presumptions. It is that which refers the main 
stages of geological change to marked eras of chemical trans- 
mutation, in the latest stages of terrestrial condensation. But 
this cannot be unfolded at the close of a paper which has 
already reached rather an undue length. 
I think I have sufficiently shown that the chief definite 
grounds, of astronomical science, upon which the doctrine of 
man's extreme antiquity has been assumed to rest, are wholly 
fallacious and unsound. 
