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Let me conclude Lowell's a priori reasoning with the strongest of his arguments (II., 39): "For proof of the continuity of the processes of both structure and change in the inorganic and organic alike, nothing at once more conclusive and more interesting can be recommended than the books of the great Haeckel." What an unfortunate reliance upon a man who has been forced to acknowledge that he has committed downright forgeries. Poor Lowell! When it comes to philosophic reasoning he is as much out of his element as his adventurous fish. As an able and persevering observer of facts he is unsurpassed. If he would only confine himself to his main and not essay the shore. It is evident that he is a rank materialist. In the two books under review there is not the least direct or indirect reference to a Creator. The word "providentially" occurs once (II., 211), and must have been an oversight; at all events it has no Christian meaning. Nature with a capital N is his god.

In his a posteriori arguments Lowell is more at home, and it is difficult and at times impossible to refute his contentions on account of his vast store of actually observed facts. Nor does the writer of these lines arrogate to himself such superior wisdom. His object is rather to present the question fairly and let the reader judge for himself.

Lowell says (II., 187) there are two most essential prerequisites to habitability, water and warmth. There is water in the polar snows, and there is also heat enough for life. Neither of these two is granted by astronomers. The presence of water has not yet been proved. That the requisite amount of heat is there can be claimed only by mathematical inference; it is certainly no fact of observation. Vegetable life can reveal itself directly (II., 188) by the coloring it imparts. Such color effects actually exist on Mars (II., 106). This astronomers are willing to concede, although most of them would grant only the lower and creeping forms of vegetation, as W. Pickering claims for parts of the moon. But animal life can reveal itself only indirectly (II., 188), not by its body, but by its mind, by the imprint it has made on the face of Mars. "Already has man begun to leave his mark on this his globe in deforestation, in canalization, in communication. But the time is coming when the earth will bear his imprint and his alone. What he chooses will survive; what he pleases will lapse, and the landscape itself become the carved object of his handiwork." (II., 109.) That this is true to the extent that the results may be seen from other planets is open to objection. Let us, however, grant it. Now, Mars bears such an imprint in his canal and oasis system. "That the canals and oases are of artificial origin," says Lowel (I., 366), "is suggested by their very look." And (I., 376) "that Mars is inhabited by beings of That Mars should age faster than the earth because it is smaller and must therefore have had a lesser sum total of the original supply of heat which all planets are losing rapidly, is another gratuitous assumption, since, as was said before, the mean temperatures of the four terrestrial planets are generally supposed to be constant, the sun supplying them with heat just as fast as they are losing it by radiation into space.

The Scientific American Supplement, No. 1764, reprints an article from the New York Sun, in which the question of the water supply of Mars is well discussed. It says: "It is argued that if the Martian atmosphere was so rich in aqueous vapor as to form these vast polar areas of ice, it would be so rich that, under any comprehensible theory of connection and atmospheric circulation, it would be impossible for it to be so arid in its equatorial and midway regions as to call for any system of irrigation at all.

"Furthermore, in opposition to the canal theory, it is held that if it really be ice at the polar caps, and knowing as we do the number of thermal units effective when the sun returns to shine upon each cap after its winter night, we cannot account for the rapidity with which the cap disappears in the sunlight. It vanishes with such speed that some observers have spoken of it as almost an evaporation, some such process as in the physics of the terrestrial atmosphere is observable in the warm Chinook winds of our northern Rocky Mountains, where whole fields of snow vanish as if dried up, the same phenomenon on the European Continent being equally familiar as the Foen of the Alps.

"So rapid is the disappearance of the bright spots in the circumpolar region when the sun dawns upon it, that it is too rapid even to admit of the inference that it is only snow. It is said that nothing but hoar frost will at all answer the conditions observed. If the Martian atmosphere has so little vapor of water that its maximum polar deposits amount to no more than frost, it is clear that the evaporation constant must be so high that no canal could possibly carry the collection of drops from a region of melting rime as far as the equator of a planet as great as our own, or beyond the equator into the cold atmosphere, as the theoretical conditions demand.

"This dilemma may thus be stated. If the water vapor in the Martian atmosphere is sufficient in amount to yield an ice cap at the polar bright spots, the tension over the rest of the planet must be such that canals will not be needed because of a sufficient precipitation; if the water vapor content is so slight that the polar caps are nothing but frost, no amount of engineering skill could cope with the tension which would evaporate whatever water may have started in the canals."

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