As for E. Williams Jackson—­the architect was also the sociologist of the four.  Moreover, he had quite a reputation as an amateur antiquarian.  Nevertheless, the most important thing about E. Williams Jackson was not learned until after the visit to Mercury, after the terrible end of that exploration, after the architect, falling in a faint, had been revived under the doctor’s care.

“Gentlemen,” said Kinney, coming from the secluded nook among the dynamos which had been the architect’s bunk; “gentlemen, I must inform you that Jackson is not what we thought.

“He—­I mean, she—­is a woman!”

Which put an entirely new face upon matters.  The three men, discussing it, marveled that the architect had been able to keep her sex a secret all the time they were exploring at Mercury.  They did not know that none of E. Williams Jackson’s fellow architects had ever guessed the truth.  Ambitious and ingenious, with a natural liking for house-planning, she had resolved that her sex should not stand in the way of success.

And when she finally came to herself, there in her bunk, and suspected that her secret was out—­instead of shame or embarrassment she felt only chagrin.  She walked, rather unsteadily, across the floor of the great cube-shaped car to the window where the three were standing; and as they quietly made a place for her, she took it entirely as a matter of course, and without a word.

The doctor had been speaking of the peculiar fitness of the four for what they were doing.  “And if I’m not mistaken,” he went on, “we’re going to need all the brains we can pool, when we get to Venus.

“I never would have claimed, when we started out, that Mercury had ever been inhabited.  But now that we’ve seen what we’ve seen, I feel dead sure that Venus once was peopled.”

The four looked out the triple-glazed vacuum-insulated window at the steadily growing globe of “Earth’s twin sister.”  Half in sunlight and half in shadow, this planet, for ages the synonym for beauty, was now but a million miles away.  She looked as large as the moon; but instead of a silvery gleam, she showed a creamy radiance fully three times as bright.

“Let’s see,” reflected the geologist aloud.  “As I recall it, the brightness of a planet depends upon the amount of its air.  That would indicate, then, that Venus has about as much as the earth, wouldn’t it?” remembering how the home planet had looked when they left it.

The doctor nodded.  “There are other factors; but undoubtedly we are approaching a world which is a great deal like our own.  Venus is nearly as large as the earth, has about nine-tenths the surface, and a gravity almost as strong.  The main difference is that she’s only two-thirds as far from the sun as we are.”

“How long is her day?” Smith wanted to know.

“Can’t say.  Some observers claim to have seen her clearly enough to announce a day of the same length as ours.  Others calculate that she’s like Mercury; always the same face toward the sun.  If so, her day is also her year—­two hundred and twenty-five of our days.”