"I dashed down-stairs, and although I could neither see nor hear it, I felt that the dog was following me. Rushing into the open air, I saw one of my men. 'Where is Ajax?' I cried. 'A very strange thing has happened, sir,' he said, 'and I should have come to tell you of it, had I not been unwilling to disturb your studies. About two hours ago Ajax was lying here in the courtyard; suddenly he sprang to his feet with a savage growl. His hair stood straight upon his back, his tail was stiff, and his lips were drawn back, showing his great teeth. I turned to see what had enraged him, but there was absolutely nothing, sir,—nothing in the world. And never did I see Ajax so angry. But this lasted only for an instant. Ajax suddenly backed, his tail dropped between his legs, his head hung down, and with a dreadful howl he turned, and, leaping the wall of the courtyard, he disappeared. I have since been watching for his return. The gate is open, and as soon as he enters I shall chain him, for I fear the dog is mad.'

"I did not dare to utter the thoughts that were in my mind, but, bidding the man inform me the moment Ajax returned, I reëntered the castle and sat down in the great hall.

"The dog was beside me; his head again lay upon my knees. With a feeling of awe, yet strangely enough without fear, I carefully passed my hand over the animal's head. I felt his ears, his nose, his jaws, and his neck. They were not the head, the ears, the nose, the jaws, or the neck of Ajax!

"I had heard of animals, and even human beings, who were totally invisible, but who still retained their form, their palpability, and all the powers and functions of life. I had heard of houses haunted by invisible animals; I had read De Kay's story of the maiden Manmat'ha, whose coming her lover perceived by the parting of the tall grain in the field of ripe wheat through which she passed, but whose form, although it might be folded in his arms, was yet as invisible to his sight as the summer air. I did not doubt for a moment that the animal that had come to me was one of those strange beings. I lifted his head; it was heavy. I took hold of a paw which he readily gave me; he had every attribute of a real dog, except that he could not be seen."

"I call that perfectly horrible," said Aunt Martha with a sort of a gasp.

"Perhaps," said the young man, "you would prefer that I should not continue."

At this both my wife and Aunt Martha declared that he must go on, and even I did not object to hearing the rest of the story.

"Well," said the young man, "Ajax never came back. It is generally believed that dogs can see things which are invisible to us, and I am afraid that my faithful hound was frightened, perhaps to death, when he found that the animal whose entrance into the courtyard he had perceived was a supernatural thing.

"But if I needed a canine companion I had one, for by day or night this invisible dog never left me. When I slept he lay on the floor by the side of my bed; if I put down my hand I could always feel his head, and often he would stand up and press his nose against me, as if to assure me that he was there. This strange companionship continued for several days, and I became really attached to the invisible animal. His constant companionship seemed to indicate that he had come to guard me, and that he was determined to do it thoroughly. I felt so much confidence in his protection, although I knew not how it could be exerted, that one morning I decided to take a walk, and with my hand on the head of the dog, to make sure that he was with me, I strolled into the open country.

"I had walked about a mile, and was approaching a group of large trees, when suddenly from behind one of them the tall figure of a man appeared. In an instant I knew it to be Colonel Kaldhein; his was a face which could not easily be forgotten. Without a word he raised a pistol which he held in his hand and fired at me. The ball whistled over my head.