Another of Mr. Romanes’ experiments on the same dog shows that the sentiment of the mysterious was, in this animal, quite powerful enough to serve as an explanation of his conduct. Having taken the terrier into a carpeted room, Mr. Romanes rolled some soap-bubbles which an unsteady draft of air blew about the carpet. The dog took a great interest in the matter, and seemed unable to decide whether the bubbles were alive or not. At first he was very prudent, and followed the bubbles at a distance, but as he was encouraged to examine them more closely, he approached them with his ears up and his tail down, in evident apprehension; the instant the bubble moved he drew back. After a time, however, during which there was at least one bubble on the floor, he took courage, and, the scientific spirit gaining the upper hand over the sentiment of mystery, he became brave enough to draw slowly near one of them and to put his paw upon it, not without anxiety. Naturally the bubble burst, and his astonishment was vivid in the extreme. Mr. Romanes made other bubbles, but could not persuade the dog to approach them for a long time. After a while, however, he started again in pursuit of one, and endeavoured with much caution to put his paw upon it. The result was the same as before. After the second attempt it was impossible to induce him to make a third, and he ultimately ran out of the room and could not be coaxed back. The same experiment, tried by Professor Delbœuf on his dog Mouston, gave a still more striking result. At the blowing of the fourth bubble, his wrath knew no bounds, but he no longer sought to seize it, he contented himself with barking at it, in all the accents of rage, until it burst. Professor Delbœuf wished to continue the experiment, and attempted to do so, but, to his great regret, was obliged to break off because of the frenzy into which the dog had worked himself. The moment that Professor Delbœuf laid his hand upon the vessel containing the soap-suds, the dog was no longer under his control. His condition was evidently due, Professor Delbœuf says, to a contradiction between the fact and his experience, that everything which is coloured is tangible. He was in the presence of the unknown, with all its mysteries and menaces; the unknown, which is the source of fear and of superstition. [Sidenote: Fear of thunder in animals due to sense of mystery.]