When Dr. Priestley settled down to writing a book, he concentrated his whole attention upon it, to the exclusion of everything else. He allowed nothing whatever to distract his mind, even for a few minutes. He lived entirely in his subject, refusing even to read the newspapers, except certain scientific periodicals which might happen to contain something relevant to the work he had in hand. As he expected his secretary to follow his example, it was hardly to be wondered at that both of them looked jaded and worn out.

“I took the manuscript to the Post Office myself, sir,” said Harold Merefield listlessly. “Here is the registration receipt.”

“Excellent, my boy, excellent,” replied the Professor, looking up. “So the work is finished at last, eh? I have been destroying such notes as we shall not require again. The rest you can file at your leisure. Dear me, you look as if you needed a change of occupation.”