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 nebulae 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 o