Such dogs become tired of waiting if their masters are absent, and are disquieted if their day's routine be changed. And you will notice in a zoölogical garden many of the better-educated animals to whom the monotony of their life is a positive sorrow, till, like opium, it stupefies their spirits. They have not the resource of man, who is also devoured with _ennui_, but, furnished with imagination, can dissipate its most tragic moods by heart-shaking and sky-splitting laughter. His most climbing grief is like an Alpine flower that sits close to the snow-line and takes its color; but near at hand are hillsides sprinkled with winking wild-flowers, and the blue succory stands amid the corn. There is but a step from one to the other. That step is taken, and the gravity of life upset whenever any of our ideas can suddenly and for a moment join an object or another idea, and appear to belong to it, though essentially different in every respect, and only capable of seeming like by the imagination starting a pretence of it. Things that are incongruous are forced to touch at one point, and for one moment to feign congruity. The surprise to the mind is a laughable one, because it is in the habit of regarding ideas and objects as they naturally cohere or differ. Sanity and business depend upon this habit. The understanding is at home in the ordinary congruities of things, and is not prepared to admit that two things which are absolutely incongruous can be ever made for a single instant to agree. Such a result cannot be soberly contemplated: the order of the world and the mental consistency which pays the butcher for his meat and the milkman for his refreshing dash of the hydrant forbid it. It becomes laughable precisely because this gravity of order is against it. If a thing cannot be done soberly, and yet _is_ done, the result is fatal to sobriety. This is the root of every laugh: two things which never met before, and ought not to meet, hail each other and set up a claim of relationship on this very ground,--namely, that it was always impossible that they could be related. In the farce of "Box and Cox," says one of these doubles to the other eagerly, "_Have you_ the mark of a strawberry between your shoulders?" "No," answers the other. "Oh, then you are indeed my long-lost brother!" It is so in the relations which make laughter. There should be the mark of a strawberry; but just because there is not, the whim of fraternity is raised, and for a moment it appears as if the two things must have been twins at birth, though separated since.