"All the common directions known to man," corrected Dr. Aiken slowly. "There is one other about which we know absolutely nothing. A direction of flight which is, at best, but a mathematical concept—"
This time Sheila Aiken stared at her father. "Daddy, it's unbelievable. You can't mean—?"
"I venture no opinion," said the old man mildly. "I am simply trying to apply to a most unusual situation the rules of logic."
Ramey gave up. He looked at the girl helplessly.
"What does he mean, Sheila?"
There was equal helplessness, and for the first time, an expression of uncertainty, in the girl's eyes as she answered. "He means—we may be moving across Time, Ramey!"
"Time!" For a moment Ramey was jarred completely out of his self-possession. Then his sense of humor came to his rescue. "Oh, come now! We are letting ourselves go hogwild! It's been a hell of a day, I know. And we've had some unnerving experiences, but—Time!"
Syd O'Brien did not share his scorn. The more sober twin nodded moodily. "Nevertheless, it's a possibility, Winters. Time is a dimension just as truly as height, breadth, depth. Some have called it the Fourth Dimension and evolved the concept of a Space-Time continuum wherein all things past and present exist side by side. Even the man-in-the-street acknowledges the dimension of Time in his everyday life. When he says he will meet a friend at Broad and Main Streets, his directions are inadequate unless he specifies the floor, for if he is on the tenth floor and his friend waits at ground level they will not meet. The third dimension, height, must be taken into consideration.
"Similarly, if he tells his friend he will meet him on the tenth floor of a building at Broad and Main, and he is there at ten o'clock but his friend does not arrive until two, they will still not meet—for they did not take into consideration the Fourth extension, Time."
"I understand that," acknowledged Ramey impatiently. "But to speak of crossing Time or 'traveling through' Time—that's absurd. Sheer nonsense for imaginative fictioneers to toy with."