him; he must be a rare clever fellow!”
“Yes,” said John, “and I would like to see the drill he used; for such a long and extremely slender tool, to be effective, must be as clever a piece of work as the steel tube.”
“I may tell you,” I proceeded, “that success was at last attained; and as a result of the comparison of our moon’s light with that of Deimos, it was shown that if the general surface brightness of the latter were equal to that of our moon, then Deimos must be only 18 miles in diameter, or about a 15,000th part of the area of our moon’s disc.
“To state the matter in another way—supposing our moon were only 18 miles in diameter, and was removed to the same distance as Deimos is from us, then it would appear only the very faint point of light that Deimos appears when viewed through the telescope.
“By the same means Phobos, the satellite nearest to Mars, was estimated to be about 22-1/2 miles in diameter. These dimensions, however, depend on the brightness of these satellites being exactly the same as the general brightness of our moon; and later experiments have fixed the sizes as 36 miles for Phobos, and 10 miles as the diameter of Deimos.
“I will not detain you much longer on this subject, as we shall be able to discuss it further when we arrive upon Mars; but I may now mention that, in one respect, the little satellite named Phobos is unique. It is the only satellite we know of which revolves round its primary planet in less time than it takes the planet itself to make one revolution on its axis.[6]
“Mars revolves on its axis in 24 hours, 37 minutes, and 22 seconds, thus the ‘day’ on Mars is nearly 38 minutes longer than our ‘day.’ Phobos revolves round the planet in the very short period of 7 hours, 39 minutes, and 14 seconds, and therefore makes more than three complete revolutions round the planet in the course of a single Martian day. The peculiar phenomena to which this very rapid motion gives rise, and the numerous eclipses which occur, will be matters of great interest to us all when we reach Mars. Our moon, as you know, takes a month to make one revolution round the earth.”
“Professor,” said John, “when we get to Mars, it will be rather a curious experience for us to see two moons shining in the sky at the same time!”
“My word!” exclaimed M’Allister, “two moons shining at once! If I go out and see such a sight as that, I shall think the whisky has been a wee bit too strong for me!”
“Well,” replied John, “if your usual drink has the effect of making you see double, take good advice, and leave the whisky severely alone when you are on Mars, or else you will be seeing four moons all at once, and receive such a shock that you will never get over it!”
M’Allister laughed pleasantly as John said this. He is a real good fellow, and takes all John’s chaff with the utmost good-humour; but, in justice to him, I must say that, although he sticks to his national drink like a true Scot, I have never once seen him any the worse for it. He knows his limitations, and always keeps within them.
CHAPTER X
THE DISCOVERY OF LINES UPON MARS—THE GREAT MARTIAN CONTROVERSY
After the little interlude with M’Allister, I resumed my remarks by saying that “The year 1877, so memorable for the near approach of Mars and the discovery of its two tiny satellites, was also the year in which a still more important discovery was made—a discovery, in fact, which has much enlarged our knowledge of the planet, and has also resulted in an entire revision of our conceptions respecting it.
“An Italian astronomer, Signor Schiaparelli, took advantage of the favourable position of Mars to observe it very carefully, and some time afterwards announced that he had seen upon its surface a number of very fine lines which had not previously been noticed, and these he had carefully charted upon his drawings and maps.
“This announcement started one of the most acrimonious discussions that the astronomical world has ever known; and although it is now over thirty years since it commenced, astronomers are still divided into two parties —one accepting the lines as demonstrated facts, the other either denying their existence, or endeavouring to explain them away by various more or less ingenious or fanciful theories.
[Illustration: From a Globe made by M. Wicks Plate VIII
MARS. MAP I
In all these maps the south is at the top. The dark shaded portions are vegetation, mostly on old sea-beds. The fine lines are the canals, and the round dots the oases. The light areas are deserts. Longitude “0” is seen on the Equator between the two forks of the “Sabaeus Sinus.”]
“When Signor Schiaparelli’s statements and drawings were first discussed, it was declared by some to be quite impossible that these fine lines could really have been seen by him: either his eyes must have been overstrained, or he claimed to see more than he actually did see. So warm did the discussion become that he soon withdrew from it altogether, but devoted himself to his work. As time went on, he not only verified his previous discoveries, but found numerous fresh lines, all of which appeared to run straight and true over many hundreds of miles on the planet.
“Milan then had a good clear atmosphere which was favourable for the observation of delicate planetary markings, and other observers who were well situated were able to see and draw many of the lines which Schiaparelli had discovered.
“It was, however, contended that such lines could not have any real existence, as it was asserted that they were too straight. It is quite true that straight lines on a rotating globe would appear curved when seen from some points of view, but if the objectors had carefully studied complete sets of drawings, they would have seen that the lines did assume a curved form in certain aspects of the planet.
“Then the very same people who denied the actuality of the lines because they were too straight, eagerly took up a suggestion that they were not actually narrow lines, but the edges of diffused shadings on the planet, apparently quite oblivious of the fact that the same objections must apply to them. Moreover, if there was difficulty in accepting the actuality of narrow lines, there must be immensely greater difficulty in believing that shadings could, in such a very large number of cases, all end in straight lines many hundreds or thousands of miles long, and always appear uniformly true, no matter upon what portion of the disc they might be seen, and whatever might be the angle of illumination.
“Besides, only a small proportion of the lines are connected with shadings. The shadings are more likely to be the result of the canals than the cause of the formation of illusory lines in so many cases.
“I have listened to many of these discussions, and have often been much amused at the tangle of inconsistencies in which some have involved themselves, by taking up fresh theories without regard to their previous contentions.
“As time went on each opposition of Mars brought the discovery of fresh lines, and numerous observers confirmed the reality of Schiaparelli’s work.
“Professor Lowell, the well-known American astronomer, took up the study of Mars in a most thorough and systematic manner, and has since practically made it his life’s work. An observatory was built at Flagstaff, Arizona, far away from towns and smoke, at an altitude of over 6000 feet above the sea-level, the site being specially selected on account of the clearness and purity of its atmosphere; while the observatory, being high up above the denser and more disturbed strata of air, afforded the most favourable situation possible for the proper observation of delicate planetary detail.
“There he continued the work which Schiaparelli had commenced, and, together with the colleagues with whom he has been associated, has, by long-continued and most systematic work, added greatly to our knowledge of Mars. Year after year has seen the addition of more lines on our maps of the planet, whilst many interesting discoveries have been made—one being that some of the fine lines were double, the second line always being equidistant from the first one throughout its whole length, no matter whether the lines were straight or curved.
“This caused a further outcry of objection. The observers were told that they had been overstraining their eyesight so that they ‘saw double,’ and also that they had been using telescopes not properly focussed. Such objections seem almost beyond argument, for no practical observer could use an improperly focussed instrument without at once discovering the defect.
