rows 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 guarderò 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
