The boy who cared for them on the voyage was disposed to play tricks on them, and one of these ugly pranks was to turn the bottle up so that when they had finished drinking and took their lips away, the water would spill out and run down over them. For a time or two they declined to drink from the bottle while he was holding it, but when he let it go it would hang in such a position that they could not get the water out of it at all. At length Aaron solved the problem by climbing up one side of the cage, and getting on a level with the bottle, reached across the angle formed by the two sides of the cage and drank. In this position it was no matter to him how much the water ran out, it couldn't touch him. Elisheba watched him until she quite grasped the idea, when she climbed up in the same manner and slaked her thirst. I scolded the boy for serving them with such cruel tricks, but it taught me another lesson of value concerning the mental resources of the chimpanzee, for no philosopher could have found a much better scheme to obviate the trouble than did this cunning little sage in the hour of necessity. I have never regarded the training of animals as the true measure of their mental powers, but the real test is to reduce the animal to his own resources, and see how he will render himself under conditions that present new problems. Animals may be taught to do many things in a mechanical way, and without any motive that relates to the action; but when they can work out the solution without the aid of man, it is only the faculty of reason that can guide them. One thing that Aaron could never figure out was what became of the chimpanzee that he saw in a mirror. I have seen him hunt for that mysterious ape for an hour at a time, and he broke a piece off a mirror I had in trying to find it, but he never succeeded. I have held the glass firmly before him, and he would put his face up close to it, sometimes almost in contact. He would quietly gaze at the image, and then reach his hand around the glass to feel for it. Not finding it, he would peep around the side of it and then look into it again. He would take hold of it and turn it around; lay it on the ground, look at the image again, and put his hand under the edge of it. The look of inquiry in that quaint face was so striking as to make one pity him. But he was hard to discourage, and continued the search whenever he had the mirror. Elisheba never worried herself much about it. When she saw the image in the glass she seemed to recognise it as one of her kind, but when it would vanish she let it go without trying to find it. In fact, she often turned away from it as though she did not admire it. She rarely ever took hold of the glass, and never felt behind it for the other ape.