The uniformity of the course of Nature will appear as the ultimate major premise of all inductions.

John Stuart Mill.

The final question is, do the lines as depicted and described by various observers exist on the surface of Mars? Those who have made the greatest addition to our knowledge of the character of these lines, and have constructed maps based on Martian latitude and longitude are accredited on other grounds as being endowed with remarkable acuteness of vision coupled with persistence and painstaking care in observation. The most successful work has been accomplished with instruments of fine definition in regions of steady atmosphere and high altitude, or at intervals of clarity and steadiness in regions otherwise unfavorable. Finally, and most convincing of all, Mr. Lowell's assistant, Mr. Lampland, after many attempts has succeeded in photographing the more conspicuous linear markings. The lines do exist essentially as figured by Schiaparelli and Lowell. It now rests with the objectors to suggest any better interpretation of the markings of Mars than that they are the results of intelligent effort.

The mediÆval attitude of some astronomers regarding this question recalls the story of Scheiner, a Jesuit brother, who, independently of Galileo and Fabricius, discovered spots on the Sun. Eager with enthusiasm he informed his Superior of his remarkable discovery and begged to be allowed to publish it to the world. The Superior replied, "Go, my son; tranquilize yourself and rest assured that what you take for spots on the Sun are the faults of your glasses or of your eyes." This happened three hundred years ago, and yet to-day a few astronomers of this class still survive.

If one will calmly reason about the matter, let him consider a parallel case of interpretation. He digs out from the ground a fragment of stone; its somewhat symmetrical shape suggests to him the idea that it may be a rude stone implement. If he wishes to know what kind of rock it is and its geological age, he refers it to a geologist; if he wishes to know its composition, he asks a mineralogist, who, if necessary, will analyze it for him. If, however, he is curious to know whether its peculiar, fractured surface is due to frost or other natural agency, or whether it is the work of some rude savage, he inquires of an archÆologist, who alone will be able to tell him whether it is a worked stone or natural fragment. He will probably tell him whether it was shaped by paleolithic man, and whether it is a rough stone implement or a core, reject or chip. So with the study of Mars, as we have already pointed out, there are certain matters of information about the planet which the astronomer alone can impart, while the superficial markings are just as certainly to be interpreted by another class of students who may or not be familiar with astronomical methods.

It was quite natural that astronomers, the most conservative of all classes of observers, should have doubted the first announcement of Schiaparelli of the startling discovery of the canali marking the face of the planet, the more so as year after year went by and yet with the utmost efforts of astronomers nothing of the nature of Schiaparelli's lines could be seen.

What added greatly to the doubt about the lines, and at the same time strengthened the idea that the lines were illusory, was the subsequent announcement by Schiaparelli?—?undeterred by the universal skepticism?—?that at times the lines appeared double. What more convincing evidence could be offered than that the phenomenon was purely subjective?

A few astronomers expressed their doubts in a courteous though hesitating manner. Professor Young, in his valuable text-book, "Elements of Astronomy" (1890), in correctly reporting Schiaparelli's discovery says: "He is so careful and experienced an observer that his results cannot be lightly rejected; and yet it is not easy to banish a vague suspicion of some error or illusion, partly because his observations have thus far received so little confirmation from others, and partly because his 'canals' are so difficult to explain. They can hardly be rivers, because they are quite straight; nor can they be artificial water-ways since the narrowest of them are forty or fifty miles wide. To add to the mystery, he finds that at certain times many of them become doubled,?—?the two which replace the former single one running parallel to each other for hundreds, and sometimes thousands, of miles, with a space of 200 or 300 miles between them. He thinks that this gemination of the canals follows the course of the planet's seasons." The overpowering belief that this world alone sustained creatures of intelligence formed an obstructive barrier to any and all attempts made to uphold?—?at least by analogy?—?the idea of intelligence in other worlds. One cannot but regret that some philosopher had not, years before Schiaparelli's time, expressed the conviction that Mars might perhaps be more favorable to the existence of intelligent life than our own world, and with this conviction proceed to formulate the conditions which must of necessity exist: namely, that the planet being a much older world than ours, its waters had mostly vanished by chemical combination with the rocks and otherwise. Following this assumption, the philosopher might have insisted that in the last extremity the melting snow caps would be utilized by the supposed intelligences to furnish water for potable and irrigating purposes. The philosopher might have superadded to this idea the prediction that, when telescopes were strong enough and eyes were keen enough, evidence of the truth of this supposition would be found in canals of some sort and that such lines should be carefully sought for. Fancy the exultation of Schiaparelli when at last he found the lines precisely as indicated. Such an announcement from so distinguished an astronomer would have been hailed with acclaim. Alas! for the conservatism of astronomers, such powers of prevision are sadly wanting. Le Verrier's prediction of an outer planet was a matter of dead certainty. The perturbations of Uranus could not be accounted for except by the assumption of an outside body, and had it not been for the characteristic reserve of English astronomers, Adams might have had the full credit. So rare are predictions of this nature in the history of astronomy that this instance will probably be quoted to the end of time. The masses, still ignorant of the certainty of mathematical astronomy, regard the prediction of an eclipse as in the nature of a prophecy. The liberal attitude of naturalists stands in marked contrast, and the history of their work is filled with examples of prediction and repeated confirmations. Until the middle of the last century?—?grounded in the belief of special creation?—?how wonderfully rapid was the conversion of naturalists to the theory of evolution after Darwin had offered his rational views on the subject. The existence of forms was predicted, based on the idea of evolution, and these have been found again and again. Our museums display in their cases remains of fossil animals which complete many series undreamed of in pre-Darwinian days. This wonderful work has been accomplished without resort to algebraic formulÆ, and yet when mathematics can be applied, as it is in the law of variation, quantitative studies in heredity, and statistical methods generally, it is promptly seized upon by the biologist.

To one unconvinced of the existence of some signs of intelligent activity in Mars the suggestions that have been made to account for certain appearances in the planet will seem absurd. If, on the other hand, he finds himself in agreement with those who believe the markings are the result of intelligent effort, then he is justified in using the various artificial markings of the surface of the Earth as standards of comparison in explaining the many curious markings of Mars. Indeed, he is compelled to do so, just as would be demanded of him if he should stand on some high mountain peak in some hitherto unexplored region of Africa and should minutely scan the hazy stretch of plains below. Large white spots in equatorial regions which could not possibly be snow-covered hills, might be masses of white flowers or cloth-covered areas for the better cultivation of certain plants. Lines that dimly stretched across the surface might be rivers, caÑons, rifts, or bands of irrigation, according to their character.

As we compare the circular markings on the Moon with our terrestrial craters and fissures, and cracks on its surface with similar fissures on the Earth, so we are forced to compare the markings on the surface of Mars with what seems analogous to them on the surface of our own Earth.

Once proved that the markings of Mars are due to erosion, cracks, encircling meteors big enough to raise ridges by their attractive force, then all that has been written in demonstration of their artificial character goes for naught. The intelligent reader unprejudiced in the matter will, however, judge for himself the merits of our contention and will determine the reasonableness of the comparisons that have been made by Lowell in solving the mystery of Mars.