Moreover, Phobos may be seen to rise as a new moon, pa.s.s through its phases to the full, wane, and again become new, all in the course of a single Martian night; or it may be seen twice full and once new during the same time.

Even this does not exhaust the list of phenomena, for, being so close to Mars, Phobos is very frequently eclipsed by the shadow of the planet.

On the other hand, the sun may be eclipsed by Phobos something like fourteen hundred times in the course of a Martian year; and, as already mentioned, the other satellite is often occulted by Phobos--sometimes when both may be only at the half full phase, and these occultations look very peculiar.

Deimos, being only 10 miles in diameter and about 12,500 miles from the surface of the planet, does not give rise to so many phenomena as the nearer satellite: still they are very numerous.

It revolves round the planet in 30-1/4 hours, but appears to take 131-1/2 hours to do so, being above the horizon about 60 hours, and below it nearly 72 hours. These are the times as seen from the equator; but, as in the case of Phobos, the farther the place is from the equator the shorter is the period that Deimos is seen above the horizon, until, when lat.i.tude 82 is reached in either hemisphere, it ceases to become visible at all.

Our moon, being so very much more distant from our earth, could be seen from both the poles.

Deimos also pa.s.ses nearly twice through all its phases whilst it is above the horizon, viz. during about 60 hours, and may be seen twice full and twice new in that time.

Eclipses of Deimos by the planet and occultations of it by the other satellite are very frequent. Being so small, it can never cause an eclipse of the sun, but it transits the sun as a dark spot about one hundred and twenty times during the Martian year.

This is really a very inadequate list of the phenomena connected with the satellites, but it will be seen that the number is enormous compared with the few eclipses of the sun or moon seen on the earth during the course of one year. Certainly Mars is an astronomer's world!

Merna heard my statements respecting these movements and phenomena as I explained them to my two friends; and when I had finished, he remarked, "You seem to be fairly well posted in these matters, sir?"

"Yes," I said; "thanks to our astronomers, both professional and amateur, all these things have been very carefully calculated; and, with the exception of a few doubtful points, we probably know nearly as much about them as the Martians themselves do."

M'Allister then turned to me and said, "Professor, you told us that the two satellites of Mars revolved round the planet in a certain time, but in each case you afterwards said they appeared to take a much longer time to do so. I'm rather puzzled to understand how that can be."

"It's really a simple matter, M'Allister," I answered, "and I think I can make it clear to you. While the satellite is making one revolution round the planet the latter is turning on its axis in the same direction as the satellite is moving, following it up in fact; and you will I think understand that in these circ.u.mstances the people on that part of the planet where the moon is visible must necessarily keep it in view for a longer period than would be the case if the planet were not revolving in the same direction.

"You have been used to being on board a ship; so suppose your vessel was steaming twelve miles an hour and there was another vessel at anchor just twelve miles ahead of you, you would reach it in just one hour, would you not?"

"Yes, certainly I should," replied M'Allister.

"Now," I continued, "suppose that the other vessel, instead of being at rest, was moving away from you at the rate of six miles an hour; after you had steamed one hour it would still be six miles ahead of you, and it would take you exactly another hour to catch it up. So you would be just double the time reaching it when moving as compared with the time required to do so when it was at anchor. This is very similar to the cases of the satellites of Mars, and much the same thing happens in regard to Mars and the earth. If they are opposite to each other at a certain point, Mars will have taken much more than one revolution round its...o...b..t before they will be opposite to each other again, because they are both moving in the same direction. Do you see it now?" I asked.

"Yes, Professor," he replied. "I know now, because you have cleared it all up. It's simple enough when one understands it."

Merna then asked me if I would like to see some of their astronomical instruments, and, on my replying that I should very much like to do so, he took us to an observatory where Corontus was at work.

I was at once struck by the small size of the telescopes; and, on inquiring about them, Corontus told me that very large instruments had long become obsolete, for these small ones could be used for all the purposes for which a large one had been required, and gave better results.

I examined one of them and found, to my surprise, that it embodied the very ideas that I had long been trying to carry into effect. With this view I had made many experiments, as it seemed to me that it ought to be possible to construct an instrument of moderate and convenient dimensions which would show as much as our monsters will show, and yet be capable of being used with low powers when occasion required. I had endeavoured to attain this result by the aid of electricity, but failed to do so. Evidently I had missed something, but here was the thing itself in successful working, as I found upon testing it.

On looking at some drawings of Saturn, which were hanging up in the observatory, I noticed that this planet was depicted with two faint outer rings which do not appear on our drawings of the planet. One of these rings has, however, been discovered by M. Jarry-Desloges, but the outermost ring is still unknown to our observers. This ring is a very broad one, its particles being widely scattered, hence its extreme faintness.

The Martians have also discovered two planets far beyond the orbit of Neptune, and their knowledge of the other planets and also of the sun and the stars is far ahead of ours.

I was also shown a comet which had recently become visible through their telescopes, and found from its position that it was undoubtedly Halley's comet, for which our astronomers were so eagerly watching. I wondered whether any of them had been fortunate enough to discover it early in August, as the Martian astronomers did. Its last appearance was in the year 1835.

John remarked that "He thought Halley's comet might be termed 'Britain's Comet,' for several of its appearances had coincided with the occurrence of very important events and turning-points in our national history, such as the Battle of Hastings, the Reformation, &c.," and he added, "as it will be a conspicuous object in our skies in 1910, I wonder whether any important event will occur in our country? In 1835, when it last appeared, we had a political crisis!"

"Well, John," I replied, "I do not attach much importance to comets as affecting mundane affairs; we have got rather beyond such beliefs as that. Besides, when we left England early in August things were going on all right in our political world, and there was no indication of any serious crisis."

"Still," said John, "it would be rather curious if we did have a crisis next year; and I should not be surprised!"

As we were walking home next day, M'Allister suddenly tripped over some little projection and fell p.r.o.ne to the ground. John ran to his a.s.sistance and raised him up, at the same time asking "If he were hurt?"

"No, not at all," said M'Allister; "I seemed to fall so lightly that I scarcely felt it when I touched the ground."

"Ah, M'Allister!" I exclaimed, "if you had fallen like that upon our earth, I think you would not have come off quite scatheless. You see, upon Mars the gravitation is much less than on the earth, being only three-eighths of what it is there, so one does not fall so swiftly, nor so heavily, as on the earth.

"You can prove that very easily. Just take up a stone and hold it out higher than your head, and let it fall; at the same time note, by the second hand of your watch, how long it takes for the stone to reach the ground."

He did so, and said that "As near as he could tell, the stone was just about one second of time in pa.s.sing from his hand to the ground."

"Just so," I replied. "On Mars a falling body only moves through a s.p.a.ce of about six feet in the first second of time. On the earth, however, the gravitation is so much greater that a falling body pa.s.ses through a s.p.a.ce of a little over sixteen feet during the first second.

"In addition to that, although you weighed twelve stones when on the earth, you only weigh about four and a half stones here upon Mars. Now you can understand why it was you seemed to fall so lightly."

"Yes, Professor," he replied, "and I'm glad I fell here, and not upon the earth!"

Then, picking up the stone again and throwing it high in the air, he watched its fall, and turning to me, remarked, "Professor, you were quite right; that stone seemed to be quite a long time coming down again, much longer than it would have been on our own world."

"Well, M'Allister," I replied, "now you know for certain that upon a small planet gravitation really is much less than upon a larger planet of the same kind.

"That's another little wrinkle for you, and you have found it all out through tripping over a stone!"

"Losh, mon," replied he, "I seem to have learnt something almost every day since I have been here; even a tumble down teaches me something!"

I then drew his attention to the birds flying near us, and pointed out that they had a much wider spread of wing than our birds have, and that this was owing to the fact that the air being so thin a wide spread of wing was absolutely necessary to support them in the air and enable them to fly. I further explained that, if the gravitation upon Mars were as great as upon the earth, the birds' wings must necessarily have been still larger, as the pull of the planet would have been so much the greater, and would thus have prevented the birds from flying at all in such thin air if their wings had been small.

"M'Allister," I then remarked, "you will, no doubt, have noticed the same thing with regard to those large and beautiful b.u.t.terflies we have seen. Why, the outspread wings of the largest must have measured ten or twelve inches across, and many of the smaller varieties were more than six inches across. I wonder what our naturalists would say if they could see some specimens of these large and splendidly coloured insects!"

"Well, Professor," he answered, "I never saw such large b.u.t.terflies anywhere else, not even when I was in the tropics on our own world. It had never occurred to me that gravitation, or even the density of the air, had anything to do with their size. Even now I do not understand how it is the small insects are able to fly, for they are heavy for their size, and do not possess very large wings, yet they can move very swiftly."

"Let me explain then," I answered. "Large birds can only move their wings with comparative slowness, and it is therefore necessary that their wings should be large to enable them to keep their balance and be able to fly. Their wings are somewhat in the nature of aeroplanes, and they shift them to different angles to take advantage of the varying currents of air.

"In the case of humming-birds and small insects, the wings are capable of intensely rapid vibrations, so rapid indeed that, when flying, the wings are almost, if not quite, invisible. This intensely rapid movement enables them to fly, and is somewhat a.n.a.logous to the rapid movements of the vertical spiral screws, which you have seen on some of the Martian air-ships that screw their way up into the air.

"Such rapid movements would not be suited to larger creatures, because their muscular powers would have to be so enormously great that their bodies would require to be larger and heavier in proportion. They would thus be very unwieldy."

CHAPTER XXIII

I HAVE A SERIOUS TALK WITH JOHN

For some days past it had been becoming more and more evident to me that John was quite infatuated with Siloni, and also that she was not unwilling to receive his attentions. I could, therefore, no longer remain a silent spectator, so took the first opportunity of our being alone to broach the subject to him.

I began by saying, "John, have you any idea of remaining upon this planet for the rest of your life?"