inspect walls and ceiling. Not that anything worth while was to be seen;
the surfaces seemed perfectly plain and bare, except for the inevitable
dust. Even the uppermost corners, ten feet above their heads, showed
dust to the light of Smith's electric torch.

Van Emmon stopped and stared at the spot as though fascinated. The
others were ready to go; they turned and looked at him curiously. For a
moment or two he seemed struggling for breath.

"Good Heavens!" he gasped, almost in a whisper. His face was white; the
other two leaped toward him, fearful that he was suffocating. But he
pushed them away roughly.

"We're fools! Blind, blithering idiots--that's what we are!" He pointed
toward the ceiling with a hand that trembled plainly, and went on in a
voice which he tried to make fierce despite the awe which shook it.

"Look at that dust again! How'd it get there?" He paused while the
others, the thought finally getting to them, felt a queer chill striking
at the backs of their necks. "Men--there's only one way for the dust to
settle on a wall! It's got to have air to carry it! It couldn't possibly
get there without air!

"That dust settled long before life appeared on the Earth, even! It's
been there ever since the air disappeared from Mercury!"



IV