Of the existence of animal life upon a far planet any evidence must, of necessity, assume a different guise from what its flora would present. Plant life should be, as on Mars we perceive it is, recognizable as part and parcel of the main features of the planet’s face. In no such forthright manner could we expect an animal revelation. The sort of testimony which would render the one patent would leave the other obstinately hid.

So long as animate life was in the lowest sense animal, it would not be seen at all, though it were as widespread as the vegetal life all about it. Reason for this lies in their receptive character. Plants are fixtures; where they start they stay; while from the nature of their food, derived directly from the soil and from the air, and conditioned chiefly by warmth and moisture, like forms inhabit large areas and by their massed effect make far impression. With animals it is otherwise. They feed by forage, from beetle to buffalo, roaming the land for sustenance. Thus, both for paucity of number and from not abiding in one stay they must escape notice at a distance such that as individuals they fail to show; to say nothing of the fact that the flora usually overtop the fauna, and so help to hide the latter while appearing itself distinct. Any far view of our earth gives instance of this. Seen from some panoramic height, forest and moorland lie patently outspread to view, yet imagination is taxed to believe them tenanted at all. Unless man have marred the landscape not a sign appears of any living thing. One must be near indeed to note even such unusual sights as a herd of buffalo in the plains or those immense flights of pigeons, that in former years occurred like clouds darkening the air. From the standpoint of another planet, through any such direct showing animal existence would still remain unknown.

Not until the creatures had reached a certain phase in evolution would their presence become perceptible; and not then directly, but by the results such presence brought to pass. Occupancy would be first evidenced by its imprint on the land; discernible thus initially not so much by the bodily as by the mind’s eye. For not till the animal had learnt to dominate nature and fashion it to his needs and ends would his existence betray itself. By the transformation he wrought in the landscape would he be known. It is thus we should make our own far acquaintance; and by the disarrangement of nature first have inkling of man.

That it is thus we should betray ourselves, a consideration of man’s history will show. While he still remained of savage simplicity, a mere child of nature, he might come and go unmarked by an outsider, but so soon as he started in to possess the earth his handicraft would reveal him. From the moment he bethought him to till the ground, he entered upon a course of world-subjugation of which we cannot foresee the end; but he has already advanced far enough to give us an idea of the process. It began with agriculture. Deforestation with its subsequent quartering of crops signalized his acquisition of real estate. His impress at first was sporadic and irregular, and in so far followed that of nature itself; but as it advanced it took on a methodism of plan. Husbandry begot thrift, and augmented wants demanded an increasing return for toil; and to this desirable end systematization became a necessity. At the same time gregariousness grew and still further emphasized the need for economy of space and time. In part unconsciously, man learnt the laws that govern the expenditure of force and more and more consciously applied them. Geometry, unloosed of Euclid, became a part of everyday life as insidiously as M. Jourdain found that he had been talking prose. Regularity rules to-day, to the lament of art. The railroad is straighter than the turnpike, as that is straighter than the trail. Communication is now too urgent in its demands to know anything but law and take other than the shortest path to its destination. Tillage has undergone a like rectification. To one used to the patchwork quilting of the crops in older lands the methodical rectangles of the farms of the Great West are painfully exact. Yet it is more than probable that these material manifestations would be the first signs of intelligence to one considering the earth from far. Our towns would in all likelihood constitute the next; and, lastly, the great arteries of travel that minister to their wants. Their scale, too, would render them the first objects to be observed. Farming as now practiced in Kansas or Dakota gives it a certain cosmical concern; fields for miles turning in hue with the rhythm of the drilled should impress an eye, if armed with our appliances, many millions of miles away.

Even now we should know ourselves cosmically by our geometrical designs. To interplanetary understanding it is this quality that would speak. Still more so will it tell as time goes on. As yet we are but at the beginning of our subjugation of the globe. We have hardly explored it all, still less occupied it. When we do so, and space shall have become enhancedly precious, directness of purpose with economy of result will have partitioned so regularly the surface of the earth as to impart to it an artificiality of appearance, and it becomes one vast coÖrdinated expanse subservient entirely to the wants of its possessors. Centres of population and lines of communication, with tillage carried on in the most economic way; to this it must come in the end.

Nor is this outcome in any sense a circumstance accidental to the earth; it is an inevitable phase in the evolution of organisms. As the organism develops brain it is able to circumvent the adversities of condition; and by overcoming more pronounced inhospitality of environment not only to survive but spread. Evidence of this thought will be stamped more and more visibly upon the face of its habitat. On earth, for all our pride of intellect, we have not yet progressed very far from the lowly animal state that leaves no records of itself. It is only in the last two centuries that our self-registration upon our surroundings has been marked. With another planet the like course must in all probability be pursued, and the older the life relatively to its habitat the more its signs of occupation should show. Intelligence on other worlds could then only make its presence known by such material revelation, and the sign-manuals of itself would appear more artificial in look as that life was high in rank. Given the certainty of plant-life, such markings are what one would look to find. Criticism which refuses to credit detail of the sort because too bizarre to be true writes itself down as unacquainted with the character of the problem. For it is precisely such detail which should show if any evidence at all were forthcoming.

If, now, we turn our inquiry to Mars, we shall be fairly startled at what its disk discloses. For we find ourselves confronted in the canals and oases by precisely the appearances a priori reasoning proves should show were the planet inhabited. Our abstract prognostications have taken concrete form. Here in these rectilineal lines and roundish spots we have spread out our centres of effort and our lines of communication. For the oases are clearly ganglia to which the canals play the part of nerves. The strange geometricism which proves inexplicable on any other hypothesis now shows itself of the essence of the solution. The appearance of artificiality cast up at the phenomena in disproof vindicates itself as the vital point in the whole matter. Like the cachet of an architect, it is the thing about the building that established the authorship.

Though the Earth and Mars agree in being planets, they differ constitutionally in several important respects. Even to us the curious network that enshrouds the Martian disk suggests handicraft; it implies it much more when considered from a Martian standpoint.