262 J. Croll—Geological Climatology. 
absorption will probably entirely disappear before the surface 
of the ground is reached. The fog will begin, of course, to 
radiate off the heat thus absorbed, but as it is the upper half 
of the mass which has received the principal part of the heat, 
the most of this heat will be radiated upward into stellar 
space, and like the reflected heat entirely lost in so far as 
heating the earth is concerned. A portion will also be radi- 
ated downward, some of which may reach the ground, but the 
greater portion will be re-absorbed in its passage through the 
; e have no means of estimating the amount of heat 
which would thus be thrown off into space by reflection and 
radiation ; but it is certainly great. I think we may safely con- 
clude that in places like South Georgia and Sandwich Land 
where fogs prevail to such an extent during summer, one half 
at least of the heat. from the sun never reaches the ground. 
A deprivation of sun heat of a much less extent than this 
would certainly lower the summer temperature of these places 
far below the freezing point, were it not for a compensating 
eause to which I shall now refer, viz: the heat “trapped” by 
the fog. The fog, although it prevents a large portion of the 
sun’s heat from ever reaching a place, at the same time pre- 
vents to a great extent that place from losing the little heat 
which it does receive. In other words, it acts as a screen pre- 
venting the loss of heat by radiation into space. But the heat 
thus “trapped” never fully compensates for that not received, 
and a lowering of temperature is always the result. 
Had all these considerations been taken into account by 
Professor Newcomb, Mr. Hill. Mr. Searles Wood and others, 
they would have seen that I had by no means over-estimated 
the powerful influence of fogs in lowering the summer temper- 
ature. 
