"Determined to get to the bottom of the mystery, Parminter, the following night, sprinkled the stairs all over with flour and sand. The same thing happened. First of all the scraping immediately overhead, then the creaking and rattling on the stairs, then the pause, and then the slow and stealthy descent, accompanied by the same combination of noises, into the hall. When all was still again, they examined the flour and sand. There were no imprints on it of any kind, and apparently it had not been touched, for it bore no sign whatever of anything having passed over it. "Still Parminter would not acknowledge the possibility of the superphysical. 'The noises we've heard,' he remarked, 'are simply the result of some curious acoustic property, not uncommon, perhaps, if we only knew it, in houses of this description. And what I saw on the stairs is, of course, merely the effect of some trick of the light which anyone who understands natural science could easily explain.' "'Well, all I can say is that I should like to have the whole thing explained, and to know what these natural causes that you're so fond of talking about really are,' rejoined Mrs. Parminter. "'So should I,' Parminter replied. 'But I can't explain it, because I'm not a scientist.' "'Well, get one,' was the reply. 'Get Professor Keipler.' "Professor Keipler was the only scientist the Parminters knew. He was a German, and at that time happened to be living in Penge. At Parminter's request he came over to Sydenham and accepted an invitation to stay the night. Parminter showed him the loft, and the Professor made a very careful examination of it, pulling up one or two boards and peering into all the cracks and crevices. He tested the walls and stairs too, and admitted that he could discern nothing there that could account for some, at least, of the noises the Parminters described. When bedtime came, instead of retiring to rest, Parminter lowered all the lights, and they all three sat on the landing and waited. "Precisely at the same time as on the previous night they heard the scraping sound in the loft, then the gentle opening of a door, then a rattling of metal; and then--Parminter caught the Professor by the arm--a long, luminous something came into view. Instead, however, of descending the stairs, it mounted the wall and suddenly shot down towards them like a streak of lightning.