counterbalanced, largely by the greater transparency to light and
heat of its thin and cloudless atmosphere, and partially also by a
greater conservative or 'blanketing' power of its atmosphere due to the
presence in it of a large proportion of carbonic acid gas and aqueous
vapour. The first of these statements may be admitted as a fact which he
is entitled to dwell upon, but the second--the presence of large
quantities of carbon-dioxide and aqueous vapour is a pure hypothesis
unsupported by any item of scientific evidence, while in the case of
aqueous vapour it is directly opposed to admitted results founded upon
the molecular theory of gaseous elasticity. But, although Mr. Lowell
refers to the conservative or 'blanketing' effect of the earth's
atmosphere, he does not consider or allow for its very great cumulative
effect, as is strikingly shown by the comparison with the actual
temperature conditions of the moon. This cumulative effect is due to the
_continuous_ reflection and radiation of heat from the clouds as well as
from the vapour-laden strata of air in our lower atmosphere, which
latter, though very transparent to the luminous and accompanying heat
rays of the sun, are opaque to the dark heat-rays whether radiated or
reflected from the earth's surface. We are therefore in a position
strictly comparable with that of the interior of some huge glass house,
which not only becomes intensely heated by the direct rays of the sun,
but also to a less degree by reflected rays from the sky and those
radiated from the clouds, so that even on a cloudy or misty day its
temperature rises many degrees above that of the outer air. Such a
building, if of large size, of suitable form, and well protected at
night by blinds or other covering, might be so arranged as to accumulate
heat in its soil and walls so as to maintain a tolerably uniform
temperature though exposed to a considerable range of external heat and
cold. It is to such a power of accumulation of heat in our soil and
lower atmosphere that we must impute the overwhelming contrast between
our climate and that of the moon. With us, the solar heat that
penetrates our vapour-laden and cloudy atmosphere is shut in by that
same atmosphere, accumulates there for weeks and months together, and
can only slowly escape. It is this great cumulative power which Mr.
Lowell has not taken account of, while he certainly has not estimated
the enormous loss of heat by free radiation, which