in Geological Climatology. 245 
quantity of heat lost by expansion must therefore be trifling 
compared with that lost by radiation ; and although the heat 
lost bv expansion is fully restored by compression, yet the air 
would reach the earth deprived almost entirely of the heat 
with which it left the equator. All that it could possibly 
give back would simply be the heat of compression ; and this 
would hardly be sufficient to raise air at —50° F. to the freez- 
ing-point. How then can the polar regions be greatly the 
better of air from the equatorial regions? Professor New- 
comb says: — "If the upper current be as great as is commonly 
supposed, it must be as powerful as ocean-currents in tending 
to equalize the temperature of the globe." flow can this be ? 
Why the Mean Temperature of the Ocean should he greater 
than that of the Land. — "Another proposition/' he says, 
'■ which the author attempts to prove, reasoning which seems 
equally inconclusive, is that the mean temperature of the 
ocean is greater than that of the land over the entire globe." 
I certainly never attempted to prove that the mean tempe- 
rature of the ocean is greater than that of the land over the 
entire globe. The very chapter to which he here refers, and 
which he is about to criticise, was written to explain why the 
mean temperature of the southern or water hemisphere is less 
than that of the northern or land hemisphere. What I at- 
tempted to prove was, not that the mean temperature of the 
ocean is greater than that of the land, but that, were it not for 
certain causes, the mean temperature of the ocean ought to be 
greater than that of the land in equatorial regions as well as 
in temperate and arctic regions. In other words, the object 
of the chapter is to prove that the mean temperature of the 
southern or water hemisphere is less than that of the northern 
or land hemisphere, not, as is generally supposed, because the 
former is mainly water and the latter land, but because of the 
enormous amount of heat transferred from the former to the 
latter hemisphere by means of ocean-currents ; and that were 
it not for this transference the temperature of the water would 
exceed that of the land hemisphere. And it is in order to 
prove this that the "four a priori reasons " which Professor 
Newcomb criticises were adduced. The first of these is as 
follows : — 
First. — ' The ground stores up heat only by the slow process 
of conduction, whereas water, by the mobility of its particles 
and its transparency for heat-rays, especially those from the 
sun, becomes heated to a considerable depth rapidly. The 
quantity of heat stored up in the ground is thus comparatively 
small, while the quantity stored up in the ocean is great.'* 
* ' Climate and Time/ p. 90. 
