This latter idiosyncrasy would, in another, have seemed either priggish or facetiously intended. With Professor Eldridge it was merely a natural method of speech. Thus, arriving once at the stroke of the dinner hour, he replied to compliments on his punctuality by remarking: "I have always considered punctuality a virtue when one is invited to partake of gratuitous nourishment." Withal, his scientific attainments were not only undoubted, but so considerable as to have won for him against many odds the reputation of a great scientist. His specialty, if such it might be called, was scientific diagnosis. The exactness of scientific laws was so admirably duplicated by the exactitudes of his mind that he seemed able, by a bloodless and mechanical sympathy, to penetrate to the most obscure causes of the strangest events. It might be added that practically his only social ties were those with the Warfords, and that the only woman with whom he ever entered into conversation was Helen. At sight of him Percy Darrow's lounging gait became accentuated to exaggeration. "Hello, Prof!" he drawled. "On the job, I see. Good morning, Doctor," he greeted Knox. "What do you make of it?" "I make of it that the Atlas Building will shortly be without tenants," replied the doctor; "me, for one." Eldridge surveyed Darrow coldly through the glittering toric lenses of his glasses. "The cause of these extraordinary phenomena is self-evident," he stated. "You mean their nature, not their cause," replied Darrow. "In nature, they refer back to the interference with etheric and molecular vibrations. That," he added, "is a fact that every boy in the grammar-school physics class has figured out for himself. The cause is a different matter." "I stand corrected," said Eldridge. "Such lapses in accuracy of statement are not usual with me, but may be considered as concomitant with unusual circumstances." "Right-o!" agreed Darrow cheerfully. "Well, what about the causes?" "That I will determine when I am satisfied that all the elements of the problem are in my hands." "Right-o!" repeated Darrow. "Well, I'll bet you a new hat I'll land the cause before you do. Be a sport!" "I never indulge in wagers," replied Eldridge. "Well," said Darrow to Jack and Hallowell, "come on!" Without waiting to see if he was followed, the young man again plunged into the black and clinging darkness. "Get hold of my coat," his voice came to the others. "We're going to climb." Accordingly they climbed, in silence, up many flights of stairs, through the cloying darkness. At last Darrow halted, turned sharp to the left, fumbled for a door, and entered a room. "Simmons?" he said. "Here!" came a voice.