Page:The New International Encyclopædia 1st ed. v. 10.djvu/358

HUMIDITY. dry air at a temperature of 100° F. will be 465 grains per cubic foot, and the combined weight of the vapor and the air, or the so-called saturated air, will be 485 grains. The following table gives these relations for saturation at a pressure of thirty inches and for temperatures between zero and a hundred, computed according to the data adopted in the Psychrometric Tables of Prof. C. F. Marvin (United States Weather Bureau, 1900):

This table shows that the capacity of the unit volume of space or air for aqueous vapor increases very rapidly with rising temperature. When the space is not saturated, the atmosphere is said to have a relative humidity expressed as a given percentage of complete saturation. Thus if the air has a temperature of 100 degrees and contains only 10 grains of vapor per cubic foot, it contains only 50 per cent. of the maximum amount possible at that temperature.

The humidity of the atmosphere is usually determined by either the dew-point apparatus or the psychrometric apparatus. In the former the air is cooled down without altering the quantity of moisture that it contains, and the temperature at which that moisture saturates the air is determined. This dew-point temperature is always lower than the temperature of the free air. In the psychrometric method the temperature of a thin layer of water that is evaporating under standard conditions in the open atmosphere is determined. From this temperature of evaporation the psychrometric formula gives us the vapor-tension, the temperature of the dew-point, and the quantity of moisture in the air. In general the temperature of the dew-point is about as far below the temperature of evaporation as the latter is below the temperature of the air.

The rate of evaporation from a moist surface diminishes with increasing humidity of the air, so that the total evaporation under a given wind in any given unit of time indicates the average dryness of the air during that time.

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. Ordinary

air cools at the rate of one degree Fahrenheit for 183 feet of ascent. In this way air that is forced over a mountain may be cooled below the dew-point and form cloud or rain. The moisture in ordinary dry air is easily absorbed by many substances, such as sugar, flour, salt, and in very moist weather objects may become so damp that fungus germs floating in the air and settling on them take root and cover them with mold, or set up fermentation within them.

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. See.  HUMILIA′TI (Lat. nom. pl., humbled). A monastic Order, which originated in the eleventh or twelfth century, and was confirmed by Innocent III. in 1201. In the sixteenth century it had 94 houses, with about 170 monks, in Italy, but as it was corrupt, (q.v.) tried to reform it. This attempt led to a murderous assault on him, so Pius V. in 1571 suppressed the Order. Several of their houses were turned over to the Barnabites.—A female Order of Benedictines, known as humiliate nuns, or nuns of Blassoni, from their founder, Clara Blassoni of Milan, served as nurses, etc. The Order still exists in Italy, with four houses.  HUMMEL, , (1778-1837). A distinguished Austrian pianist and composer, born at Pressburg and educated primarily by his father, who was a music-teacher. When but eight years of age he accompanied his father to Vienna on the appointment of the latter as kapellmeister of Schikaneder's Theatre. Here he came under the notice of Mozart, who became so interested in the boy that he admitted him to his own family and instructed him for two years. His début in 1787 was also under the auspices of Mozart. Next followed a number of very successful tours through Germany, Denmark, England, and Holland. Probably no other musician in the entire history of music had so distinguished a number of teachers and patrons as Hummel. Beginning with Mozart, his next teacher was Clementi, with whom he studied in London during 1791, followed by a course of study in composition under Albrechtsberger in Vienna (1793), while at the same time he was studying with Salieri in dramatic writing, and receiving much indirect, but nevertheless 