Professor Dove has shown, by taking at all seasons the mean of the
temperature of points diametrically opposite to each other, that the
mean temperature _of the whole earth’s surface_ in June considerably
exceeds that in December. This result, which is at variance with the
greater proximity of the sun in December, is, however, due to a totally
different and very powerful cause,--the greater amount of land in
that hemisphere which has its summer solstice in June (_i. e._ the
northern); and the fact is so explained by him. The effect of land
under sunshine is to throw heat into the general atmosphere, and to
distribute it by the carrying power of the latter over the whole earth.
Water is much less effective in this respect, the heat penetrating its
depths and being there absorbed; so that the surface never acquires
a very elevated temperature, even under the equator.--_Sir John
Herschel’s Outlines._