"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 orbit 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.