Suddenly Jackson straightened up and looked about with a new interest.
He went to one of the square doorways and very carefully removed the
dust from a small plate on the lintel. He need not have been so careful;
engraved in the solid metal was a single character, plainly in the same
language as the other ideographs.

The architect smiled triumphantly into the inquiring eyes of his
friends. "I won't have to eat my hat," said he. "This is a sure-enough
city, all right, and this is its library!"

Smith was still busy on the little machine when they returned to the
cube. He said that one part of it had disappeared, and was busily
engaged in filing a bit of steel to take its place. As soon as it was
ready, he thought, they could see what the apparatus meant.

The three had brought a large number of the reels. They were confident
that a microscopic search of the ribbons would disclose something to
bear out Jackson's theory that the great structure was really a
repository for books, or whatever corresponded with books on Mercury.

"But the main thing," said the doctor, enthusiastically, "is to get over
to the 'twilight band.' I'm beginning to have all sorts of wild hopes."

Jackson urged that they first visit the big "mansion" on the outskirts
of this place; he said he felt sure, somehow, that it would be worth
while. But Van Emmon backed up the doctor, and the architect had to be
content with an agreement to return in case their trip was futile.

Inside of a few minutes the cube was being drawn steadily over toward
the left or western edge of the planet's sunlit face. As it moved, all