Adding to this, that the force of gravity on Mars is nearer that of the moon than to that of the earth, and we may r reasonably conclude that its surface is formed of volcanic matter in a light and porous condition, and therefore highly favourable for the rapid loss of surface heat by radiation.

The surface-conditions of Mars are therefore, presumably, much more like those of the moon than like those of the earth.
The next condition favourable to the storing up of heat--a covering of vegetation--is almost certainly absent from Mars except, possibly, over limited areas and for short periods.

In this feature also the surface of Mars approximates much nearer to lunar than to earth-conditions.

The third condition--a dense, vapour-laden atmosphere--is also wanting in Mars.

For although it possesses an atmosphere it is estimated by Mr.
Lowell (in his latest article) to have a pressure equivalent to only 2-1/2 inches of mercury with us, giving it a density of only one-twelfth part that of ours; while aqueous vapour, the chief accumulator of heat, cannot permanently exist in it, and, notwithstanding repeated spectroscopic observations for the purpose of detecting it, has never been proved to exist.
I submit that I have now shown from the statements--and largely as the result of the long-continued observations--of Mr.Lowell himself, that, so far as the physical conditions of Mars are known to differ from those of the earth, the differences are all _unfavourable_ to the conservation and _favourable_ to the dissipation of the scanty heat it receives from the sun--that they point unmistakeably towards the temperature conditions of the moon rather than to those of the earth, and that the cumulative effect of these adverse conditions, acting upon a heat-supply, reduced by solar distance to less than one-half of ours, _must_ result in a mean temperature (as well as in the extremes) nearer to that of our satellite than to that of our own earth.
_Further Criticism of Mr.Lowell's Article._ We are now in a position to test some further conclusions of Mr.
Lowell's _Phil.