And again the doctor was a witness to a clash of eyes between the girl and the geologist.  Van Emmon said nothing further, however, but turned to examine an immense book-case on the other side of the room.

This case had shelves scarcely two inches apart, and about half as deep, and held perhaps half a million extremely small books.  Each comprised many hundreds of pages, made of a perfectly opaque, bluish-white material of such incredible thinness that ordinary India-paper resembled cardboard by comparison.

They were printed much the same as any other book, except that the characters were of microscopic size, and the lines extremely close together.  Also, in some of the books these lines were black and red, alternating.

Billie eagerly examined one of the diminutive volumes under a strong glass, and pronounced the black-printed characters not unlike ancient Gothic type.  She guessed that the language was synthetic, like Roman or Esperanto, and that the alphabet numbered sixty or seventy.

“The red lines,” she added, not so confidently, “are in a different language.  Looks wonderfully like Persian.”  By this time the others were doing the same as she, and marveling to note that, wherever the red and black lines were employed, invariably the black were in the same language; while the red characters were totally different in each book.

Suddenly Smith gave a start, so vigorously that the other turned in alarm.  He was holding one of the books as though it were white hot.  “Look!” he stuttered excitedly.  “Just look at it!”

And no wonder.  In the book he had chanced to pick up, the red lines were printed in English.

“Talk about your finds!” exclaimed Billie, in an awe-struck tone.  “Why, this library is a literal translation of the languages of—­” she fairly gasped as she recalled Myrin’s words—­“thousands of planets!”

After that she fell silent.  Plainly the discovery had profoundly affected and strengthened her notion of remaining on the planet.  Van Emmon, watching her narrowly, saw her give the room an appraising glance which meant, plain as day, “I’d like to keep this place in spick and span condition!” And another, not so easy to interpret:  “I’d like to show these people a thing or two about designing houses!” And the geologist’s heart sank for an instant.

He turned resolutely to the bookcase, and shortly found something which he showed to the doctor.  It was a book printed all in “Venusian.”  They carefully translated the title-page, using one of the interlinear English books as a guide; and saw that it was a complete text-book on astral development.

“With these instructions,” the doctor declared, “any one could do as the Venusians do—­visit other worlds in spirit!”

Just then Estra and Myrin returned.  They were moving at what was, for them, a rapid pace; and to all appearances they were rather excited.