He looked up at the sun, and saw that it was almost exactly where it had been, and that it had not perceptibly diminished in power.
The idea was not at all pleasant to him, and very naturally his thoughts turned back once more to his cosy home that had been on the edge of Wimbledon Common ten thousand years ago.

He remembered, with a curious sort of thrill, some notes which he had to complete that morning for his lecture--and in the same instant he was walking back across the turf towards his house through the warm May sunshine.
"Yes," he said to himself, as he drew a deep breath of the sweet spring air.

"I was right; that's it.

The fourth dimension is a form of duration in some way correlated with space.

I shall have to work that out in the light of the greater knowledge, which Her vanished Majesty has given me, and which I almost attained to in Egypt.