"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.