S. Newcomb—Some points in Climatology. 25 
temperatures and not quantities of heat with which we are 
ultimately concerned and the inconclusive character of the 
reasoning will be at once apparen 
I shall next pass to the question of the non-melting of snow 
during a short perihelion summer, in which, as I stated in my 
former review, calculating temperatures by Mr. Croll’s formula, 
should have a mean temperature ranging from 100° to 
150° Fahr. I had to acknowledge some embarrassment from 
Mr. Croll’s causes producing their effects through the two dia- 
metrically opposite modes of operation, to wit: 
Ist. By making the air exceedingly transparent and thus 
e. 
see no use in arguing this point for the simple reason that 
T do not know enough about the relations of temperature to 
the aqueous vapor in the atmosphere to admit of my saying 
anything of value on the subject. I would merely remark 
that I cannot see in Mr. Croll’s reasoning the slightest ground 
for admitting that the perihelion summer radiation would pro- 
‘ce any other effect than it does now. Be 
L am surprised that Mr. Croll should have been willing to 
 Pigeoge reasoning so obviously inconclusive as that in which 
1¢ endeavors to show that my objection to the reliableness of 
his dates for glacial epochs, on account of the insufficiency of 
the fundamental data for the secular variations of the plane- 
tary orbits, falls to the ground. My objection and his state- 
ment in reply I can leave to the judgment of the reader who 
chooses to refer to them. pe 
I conceive that some general remarks on the nature of the 
problem will be of more value than a further analysis of Mr. 
Croll’s reasoning. It is an observed fact that we now have a 
