“ The humidity of the atmosphere, although invisible, has a special and strong influence in absorbing radiant energy, whether from the sun or from the earth. It therefore converts the dry air into a powerful obstructor to the passage of radiant heat, and by this means the humid atmosphere is made to act as a blanket, keeping the earth and the lower air much warmer than it would otherwise be. ”

“ Nearly all animal and vegetable substances, by reason of their cellular structure, absorb moisture from moist air, but give it up to very dry air. They are, therefore, perpetually expanding and contracting, curling and uncurling, and their changes may be utilized in the construction of hygrometers. When moist air cools by radiation at night to temperatures below the dew-point, the vapor is precipitated, forming cloud, mist, fog, or dew. On the other hand, when air rises, thereby coming imder less pressure, it expands, does work, and is cooled dynamically by reason of the work done. ”

“ The elastic pressure of the dry air and the elastic pressure of the aqueous vapor added together produce what is ordinarily called barometric or atmospheric pressure. The weight of the moisture and the weight of the dry air added together determine the density of a cubic foot of atmosphere at any time. When a cubic foot of space contains as much aqueous vapor as it can possibly hold at any given temperature, it is said to be saturated with moisture. ”