These things must all be reckoned with before anything certain can be known of the surface of Mars. The difficulty of pronouncing upon the minute details is impressively indicated by Professor Moulton, who says that, even under the finest conditions and with the best telescopes, it is like viewing “a perfectly accurate relief map of the whole United States made on such a scale that it would be only three inches in diameter and held at a distance of three feet from the eye.” Under such a near limit of vision, we can well see that differences of opinion might arise. The mere fact that some astronomers have not seen the lines on Mars does not mean that they deny their existence. Some eyes have greater defining power than others, as well as some telescopes, as every one knows. But while all the lines and patches of color that are claimed to have been seen on Mars doubtless have been seen by some persons, yet it is not necessary to accept the interpretation of them given by lively-minded observers when it is not convincing. There may be vegetation on Mars, and even intelligent beings. We do not know; and thus far there is not much to support, even by inference, the view that there are. If we want the truth, we are brought no nearer to it by giving full credence to a speculative theory simply because it is interesting and pleasant; and thus far all theories advanced as to the nature of the surface markings on Mars are speculations, though there is no doubt that the marks are there. It is pleasing, however, to contemplate the idea of there being on Mars, or on any other planet, an active intelligence of any sort resembling what we have here on earth, and it is not strange that such a wide-spread popular interest should attach to Mars, in view of what has been suggested by the markings on its surface. THE SATELLITES OF MARS