of sardines, a
can-opener, and half a loaf of bread.

"I had to select my supplies rather at random," she said, "and you'll
have to make the best of them."

She started to open the sardines. "You'd better give it to me," Dan
advised. "You might cut your hand."

"You think so?" she asked, deftly lifting the lid, fishing out a fish
for the kitten, and presenting the can to Dan. Then with capable
hands she broke off a large chunk of bread, which she handed him.

"Go ahead and finish this up," she said. "I've already had breakfast."
She punched two holes in the end of the milk can, and poured some of
the thick yellow fluid into the palm of her left hand, from which she
let the kitten lap it.

"And now for the mystery of the island," Dan demanded, forgetting
bread and sardines in his eagerness.

* * * * *

The girl turned her face to him. "I'm Helen Hunter, as you seem to
know," she began. "I came here with my father five years ago to
observe an eclipse of the sun. When it was all over, and the ship
called to take us off, he decided to send the results of our
observations by one of the other men. He wanted to stay here to carry
on another experiment--the one that led to that machine on the hill.
Part of the other men were willing to stay. The yacht left us here,
and has been back from San Francisco every six months since, with mail
and supplies."

"And what was the experiment?" Dan demanded eagerly.

"Have you ever looked at Mars through a good telescope?" she
countered. "Then you must have seen the canals--straight dark lines
running from the white polar caps to the equatorial zone. All
scientists did not agree as to what they were, but nobody could
suggest a natural origin for them.

"My father was one of those who thought that the canals were fertile,
cultivated strips, irrigated with water brought down from the melting
ice-caps. Irrigation systems meant intelligent life upon the planet,
and his experiment was an attempt to communicate with that
intelligence."

"And he succeeded?" Dan was astounded.

"Yes. The means was simple enough: other men had suggested it years
before, in fact. Any fairly bright light on Mars--such as the beam of
a searchlight directed toward earth--would be visible in a good
telescope, when the planet is favorably situated: it follows that such
a light on earth should be visible to an observer with a similar
instrument on Mars.

"It was possible, o