ists will account for the peculiar
whiteness at the edge of the limb, and an occasional veiling of the
landscape."

While he spoke, my attention was suddenly arrested by a vivid point of
light which appeared on the dark side of the terminator, and south of
the equator.

"Hallo!" I exclaimed, involuntarily. "There's a light!"

"Really!" responded Gazen, in a tone of surprise, not unmingled with
doubt. "Are you sure?"

"Quite. There is a distinct light on one of the continents."

"Let me see it, will you?" he rejoined, hastily; and I yielded up my
place to him.

"Why, so there is," he declared, after a pause. "I suspect it has been
hidden under a cloud till now."

We turned and looked at each other in silence.

"It can't be the light Javelle saw," ejaculated Gazen at length. "That
was on Hellas Land."

"Should the Martians be signalling they would probably use a system of
lights. I daresay they possess an electric telegraph to work it."

The professor put his eye to the glass again, and I awaited the result
of his observation with eager interest.

"It's as steady as possible," said he.

"The steadiness puzzles me," I replied. "If it would only flash I should
call it a signal."

"Not necessarily to us," said Gazen, with mock gravity. "You see, it
might be a lighthouse flashing on the Kaiser Sea, or a night message in
the autumn manoeuvres of the Martians, who are, no doubt, very warlike;
or even the advertisement of a new 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 nebulae, 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 instanc