On it floats the melody of waves, the song of birds, the human voice. As the air is penetrable to the eager eye in all directions, so it throbs far and near in motion for the attentive ear, laden with the sweet speech of nature and of man. Nor is this the only sense it addresses, it bears fragrance to the nostrils, and brushes, with lightest feather, the face and flesh of man.

In like manner it is a controlling agent in the diffusion of heat, turning it into a pervasive and genial presence, in place of intense alternations of heat and cold alike unbearable. This service it performs, directly, by its own currents traversing the globe, and also, indirectly, in connection with vapor. The atmosphere is porous as a sponge to vapor. Vast amounts, with an incredible expenditure of energy, are taken up, borne far and near, and let fall as rain on ocean, upland and mountain. This aqueous circulation is the blood-circulation of the globe, and is maintained with an abundant yield of mechanical and vital force, and a prodigal expression of beauty. In this process heat is the chief agent, while it itself is wonderfully spread and equalized by it.

The average amount of vapor in the air is one part in seventy. The capacity of the atmosphere in this particular is a point of utmost moment, as the watering of the earth turns upon it. A little excess in either direction is fatal to vegetable or animal life or both. The rain-fall is comparatively equable in all fertile and salubrious portions of the globe. A little failure here dooms a region to barrenness.