Presently he felt that he understood the Sanusian situation.  He fell silent; and Rolla, after waiting as long as her patience would allow, finally put the question temporarily uppermost in her mind: 

“It is true that I have crossed the edge of the world.  And yet, I understand it not at all.  Can ye explain the nature of this strange world we live upon, Somat?” There was infinite respect in the way Rolla used his name; had she known a word to indicate human infallibility, such as “your majesty,” she would have used it.  “There is a saying among our people that the world be round.  How can this be so?”

“Yet it is true,” answered Somat, “although ye must know that it be not round like a fruit or a pebble.  No more is it flat, like this,” indicating the lid of the stove, near which they sat.  “Instead, ’tis shaped thus”—­and he took from his finger a plain gold band, like an ordinary wedding ring—­“the world is shaped like that!”

Rolla examined the ring with vast curiosity.  She had never seen the like before, and was quite as much interested in the metal as in the thing it illustrated.  Fortunately the band was so worn that both edges were nearly sharp, thus corresponding with the knifelike ridge over which she had crawled.

“Now,” Somat went on, “ye and your people live on the inner face of the world,” indicating the surface next his skin, “while I and my kind live on the outer face.  Were it not for the difficulties of making the trip, we should have found you out ere this.”

Rolla sat for a long time with the ring in her hand, pondering the great fact she had just learned.  And meanwhile, back on the earth, four excited citizens were discussing this latest discovery.

“An annular world!” exclaimed the doctor, his eyes sparkling delightedly.  “It confirms the nebular hypothesis!”

“How so?” Smith wanted to know.

“Because it proves that the process of condensation and concentration, which produces planets out of the original gases, can take place at uneven speeds!  Instead of concentrating to the globular form, Sanus cooled too quickly; she concentrated while she was still a ring!”

Smith was struck with another phase of the matter.  “Must have a queer sort of gravitation,” he pointed out.  “Seems to be the same, inside the ring or outside.  Surely, doc it can’t be as powerful as it is here on the earth?”

“No; not likely.”

“Then, why hasn’t it made a difference in the inhabitants?  Seems to me the humans would have different structure.”

“Not necessarily.  Look at it the other way around; consider what an enormous variety of animal forms we have here, all developed under the same conditions.  The humming-bird and the python, for instance.  Gravitation needn’t have anything to do with it.”

Billie was thinking mainly of the question of day and night.  “The ring must be inclined at an angle with the sun’s rays,” she observed.  “That being the case, Sanus has two periods each year when there is continuous darkness on the inner face; might last a week or two.  Do you suppose the people all hibernate during those seasons?”