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. Mag._ article by comparison with actual phenomena. We have seen, in the outline I have given of this article, that he endeavours to show how the small amount of solar heat received by Mars is 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