on second thought. For the intrinsic improbability of such a state of things arising from purely natural causes becomes evident on a moment's consideration.

If lines be drawn haphazard over the surface of a globe, the chances are ever so many to one against more than two lines crossing each other at any point. Simple crossings of two lines will of course be common in proportion to the sum of an arithmetical progression; but that any three lines should contrive to cross at the same point would be a coincidence whose improbability only a mathematician can properly appreciate, so very great is it. If the lines were true lines, without breadth, the chances against such a coincidence would be infinite, that is, it would never happen; and, even had the lines some breadth, the chances would be great against a rendezvous. In other words, we might search in vain for a single instance of such encounter. On the surface of Mars, however, instead of searching in vain, we find the thing occurring passim; this a priori most improbable rendezvousing proving the rule, not the exception. Of the crossings that are best seen, all are meeting-places for more than two canals.

To any one who had not seen the canals, it might occur that something of the same improbability would be fulfilled by cracks radiating from centres of explosion or fissure. But such a supposition is at once negatived by the uniform breadth of the lines, a uniformity impossible in cracks, whose very mode of production necessitates their being bigger at one end than at the other. We see examples of what might result from such action in the cracks that radiate from Tycho, in the Moon, or, as we now know from Professor W. H. Pickering's observations, from the craterlets about it. These cracks bear no resemblance whatever to the lines on Mars. They look like cracks; the lines on Mars do not. Indeed, it is safe to say that the Martian lines would never so much as suggest cracks to any one. Lastly, the different radiations fit into one another absolutely, an utter impossibility were they radiating rifts from different centres.

In the same way we may, while we are about it, show that the lines cannot be several other things which they have more or less gratuitously been taken to be. They cannot, for example, be rivers; for rivers could not be so obligingly of the same size at source and mouth, nor would they run from preference on arcs of great circles. To do so, practically invariably, would imply a devotion to pure mathematics not common in rivers. They may, in some few instances, be rectified rivers, which is quite another matter. Glaciation cracks are equally out of the question,--first, for the causes above mentioned touching cracks in general; and second, because there is, unfortunately, no ice where they occur. Nor can the lines be furrows ploughed by meteorites,--another ingenious suggestion,--since, in order to plough, invariably, a furrow straight from one centre to another, without either missing the mark or overshooting it, the visitant meteorite would have to be specially trained to the business.

Such are the chief purely natural theories of the lines, excluding the idea of canals,--theories advanced by persons who have not seen them. No one who has seen the lines well could advance them, inasmuch as they are not only disproved by consideration of the character of the lines, but instantly confuted by the mere look of them.

Schiaparelli supposes the canals to be canals, but of geologic construction. He suggests, however, no explanation of how this is possible; so that the suggestion is not, properly speaking, a theory. That eminent astronomer further says of the idea that they are the work of intelligent beings: "Io mi guardero bene dal combattere questa supposizione, la quale nulla include d'impossibile." (I should carefully refrain from combating this supposition, which involves no impossibility.) In truth, no natural theory has yet been advanced which will explain these lines.

Their very aspect is such as to defy natural explanation, and to hint that in them we are regarding something other than the outcome of purely natural causes. Indeed, such is the first impression upon getting a good view of them. How instant this inference is becomes patent from the way in which drawings of the canals are received by incredulously disposed persons. The straightness of the lines is unhesitatingly attributed to the draughtsman. Now this is a very telling point. For it is a case of the double-edged sword. Accusation of design, if it prove not to be due to the draughtsman, devolves ipso facto upon the canals.