“You saw his ghost, I guess, Miss Forsdyke--and that’s all there is to it.” Captain Sergeantson lit himself another cigar by way of showing how cold-blooded he could be in the possible presence of a spectre. Jimmy shuddered. “It’s uncanny,” he said. “I don’t like it.” “But _why_?” puzzled Hetty, wrinkling her brows. She turned to her father. “Poppa----!” Forsdyke shook his head smilingly. “I’m out of this deal. Ask the Professor. He’s the authority on spooks. What does it all mean, Lomax? Can you give an explanation that doesn’t outrage commonsense?” The Professor smiled. The eyes in that clean-cut face twinkled. “Commonsense?” He shrugged his shoulders. “We want to start by defining that--by defining all our senses--and we should never finish.” He looked with his challenging smile round the group. “I see you are inviting me to throw away my last little shred of reputation as a sane,” he said, humorously. “Well, I will not venture on any explanation of my own. The evidence, with all respect to Hetty here, is insufficient. We only know that she had a dream and a hallucination twice repeated. We know that the hallucination corresponds to a photograph in Captain Sergeantson’s pocket. We do not know what basis there is--if any--for her dream. But I will give you two alternative explanations that might be suggested by other people.--Will that satisfy you?” “Go ahead, Professor,” said Forsdyke. “Don’t ask me to believe in ghosts, that’s all!” “I don’t ask you to believe in anything,” replied the Professor. “I don’t ask you to believe in the reality of your presence and ours in this room. If you have ever read old Bishop Berkeley you will know that you would find it exceedingly difficult to evade the thesis that it may all be an illusion. Your consciousness--whatever that is--builds up a picture from impressions on your senses. You can’t test the reality of the origin of those impressions--you can only collate the subjective results. Everything--Time and Space--may be an illusion for all you or I know!” “I heard that in my dream!” Hetty broke in. “Someone said it: ‘Time and Space are an illusion!’ I remember it so clearly now!” Her eyes glistened with excitement. “All right, Hetty,” said her father. “Let the Professor have his say. It’s his turn. And don’t take us out of our depth, Lomax. You know as well as I do what I mean by commonsense.” The Professor laughed.