soap."

"Seriously, what do you think of it?" I asked.

"I confess it's a mystery to me," he answered, pondering deeply; and then, as if struck by a sudden thought, he added: "I wonder if it's any good trying the spectroscope on it?"

So saying, he attached to the telescope a magnificent spectroscope, which he employed in his researches on the nebulæ, and renewed his observation.

"Well, that's the most remarkable thing in all my professional experience," he exclaimed, resigning his place at the instrument to me.

"What is?" I demanded, looking into the spectroscope, where I could distinguish several faint streaks of coloured light on a darker background.

"You know that we can tell the nature of a substance that is burning by splitting up the light which comes from it in the prism of a spectroscope. Well, these bright lines of different colours are the spectrum of a luminous gas."

"Indeed! Have you any idea as to the origin of the blaze?"

"It may be electrical—for instance, an aurora. It may be a volcanic eruption, or a lake of fire such as the crater of Kilauea. Really, I can't say. Let me see if I can identify the bright lines of the spectrum."

I yielded the spectroscope to him, and scarcely had he looked into it ere he cried out—

"By all that's wonderful, the spectrum has changed. Eureka! It's thallium now. I should know that splendid green line amongst a thousand."

"Thallium!" I exclaimed, astonished in my turn.

"Yes," responded Gazen, hurriedly. "Make a note of the observation, and also of the time. You will find a book for the purpose lying on the desk."

I did as directed, and awaited further orders. The silence was so great that I could plainly hear the ticking of my watch laid on the desk before me. At the end of several minutes the professor cried—

"It has changed again: make another note."

"What is it now?"

"Sodium. The yellow bands are unmistakable."

A deep stillness reigned as before.

"There she goes again," exclaimed the professor, much excited. "Now I can see a couple of blue lines. What can that be? I believe it's indium."

Another long pause ensued.

"Now they are gone," ejaculated Gazen once more. "A red and a yellow line have taken their place. That should be lithium. Hey, presto!—and all was dark."

"What's the matter?"

"It's all over." With these words he removed the spectroscope from the telescope, and gazed anxiously at the planet "The light is gone," he continued, after a minute. "Perhaps another cloud is passing over it. Well, we must wait. In the meantime let us consider the situation. It seems to me that we have every reason to be satisfied with our night's work. What do you think?"

There was a glow of triumph on his countenance as he came and stood before me.

"I believe it's a signal," said I, with an air of conviction.

"But how?"

"Why should it change so regularly? I've timed each spectrum, and found it to last about five minutes before another took its place."

The professor remained thoughtful and silent.

"Is it not by the light which comes from them that we have gained all our knowledge of the constitution of the heavenly bodies?" I continued. "A ray from the remotest star brings in its heart a secret message to him who can read it. Now, the Martians would naturally resort to the same medium of communication as the most obvious, simple, and practicable. By producing a powerful light they might hope to attract our attention, and by imbuing it with characteristic spectra, easily recognised and changed at intervals, they would distinguish the light from every other, and show us that it must have had an intelligent origin."

"What then?"

"We should know that the Martians had a civilisation at least as high as our own. To my mind, that would be a great discovery—the greatest since the world began."

"But of little use to either party."

"As for that, a good many of our discoveries, especially in astronomy, are not of much use. Suppose you find out the chemical composition of the nebulæ you are studying, will that lower the price of bread? No; but it will interest and enlighten us. If the Martians can tell us what Mars is made of, and we can return the compliment as regards the earth, that will be a service."

"But the correspondence must then cease, as the editors say."

"I'm not so sure of that."

"My dear fellow! How on earth are we to understand what the Martians say, and how on Mars are they to understand what we say? We have no common code."

"True; but the chemical bodies have certain well-defined properties, have they not?"

"Yes. Each has a peculiarity marking it from all the rest. For example, two or more may resemble each other in colour or hardness, but not in weight."

"Precisely. Now, by comparing their spectra can we not be led to distinguish a particular quality, and grasp the idea of it? In short, can the Martians not impress that idea on us by their spectro-telegraph?"

"I see what you mean," said Professor Gazen; "and, now I think of it, all the spectra we have seen belong to the group called 'metals of the alkalies and alkaline earths,' which, of course, have distinctive properties."

"At first, I should think the Martians would only try to attract our notice by striking spectra."

"Lithium is the lightest metal known to us."

"Well, we might get the idea of 'lightness' from that."

"Sodium," continued the professor, "sodium is a very soft metal, with so strong an affinity for oxygen that it burns in water. Manganese, which belongs to the 'iron group,' is hard enough to scratch glass; and, like iron, is decidedly magnetic. Copper is red—"

"The signals for colour we might get from the spectra direct."

"Mercury or quicksilver is fluid at ordinary temperatures, and that might lead us to the idea of movement—animation—life itself."

"Having got certain fundamental ideas," I went on, "by combining these we might arrive at other distinct conceptions. We might build up an ideographic or glyphic language of signs—the signs being spectra. The numerals might be telegraphed by simple occultations of the light. Then from spectra we might pass by an easy step to equivalent signals of long and short flashes in various combinations, also made by occulting the light. With such a code, our correspondence might go on at great length, and present no difficulty; but, of course, we must be able to reply."

"If the Martians are as clever as you are pleased to imagine, we ought to learn a good deal from them."

"I hope we may, and I'm sure the world will be all the better for a little superior enlightenment on some points."

"Well, we must follow the matter up, at all events," said the professor, taking another peep through the telescope. "For the present the Martian philosophers appear to have shut up shop; and, as my nebula has now risen, I should like to do a little work on it before daybreak. Look here, if it's a fine night, can you join me to-morrow? We shall then continue our observations; but, in the meanwhile, you had better say nothing about them."

On my way home I looked for the ruddy planet as I had done in the earlier part of the night, but with very different feelings in my heart. The ice of distance and isolation separating me from it seemed to have broken down since then, and instead of a cold and alien star, I saw a friendly and familiar world—a companion to our own in the eternal solitude of the universe.

CHAPTER II.

HOW CAN WE GET TO THE OTHER PLANETS?

The next evening promised well, and I kept my appointment, but unfortunately a slight haze gathered in the sky and prevented us from making further observations. While hoping in vain for it to clear away, Professor Gazen and I talked over the possibility of journeying to other worlds. The gist of our