RAIMUND DE SABUNDE, ri'moond si-boon'di, scholastic philosopher: b. Barcelona. In 1436 he appears at Toulouse as a teacher of medicine, philosophy and theology, and he labored especially to reconcile the apparent con tradictions between nature or reason and the Bible, an undertaking which led him into the realm of mysticism. In his Creaturarum seu Theologise Naturalis> he applied this prin ciple so as_practically to reconstruct the whole system of Church doctrine. He and his system have been discussed by Matzke (1846), Hunks' (1851) and F. Nitzsch in the fur histonsche Theologie> (1859).
RAIN (Lat. nigare; Gk. 014Xeiv, to wet), water dropping through the atmosphere. A mass of air in the atmosphere always contains some aqueous vapor, and if this air is cooled below a certain temperature, called the dew point (which depends on the amount of vapor present), the vapor will condense into drops of water. • The cooling may be. due to radiation of heat to colder regions or to mixture with colder masses of air. When air rises in the atmosphere to colder regions, or comes in con tact with a cold part of the earth, or passes from equatorial to polar parts of the earth, its moisture tends to condense into rain. In con sidering the probable rainfall of a place we are concerned with its latitude, its elevation above the sea, its proximity to the sea, the laws affect ing its seasonable variations, the prevailing winds and the configuration of the surrounding surface. Low latitudes have in general a heavy rainfall, because of the •greater evaporation in tropical regions, and the consequent formation of rain when the clouds due to evaporation get colder in the higher regions of the atmosphere. Hence also winds blowing from the equator are generally moist and winds blowing to the equator are generally dry. The presence of forests tends to increase the rainfall (see Me•rionoLoov), and the rain further, encourages vegetation. Over the ocean the skies are clear where the trade-winds are blowing steadily, and heavy rain falls by day in the zone of calms; on land there is a regular alternation of dry and wet seasons. Toward the equator, where there is a considerable interval between the two passages of the sun across the zenith, there are two rainy seasons. In monsoon re gions, however, the alternation of dry and wet seasons depends on the winds. Beyond the tropics we have variable winds and variable rainfall. The following table gives recent figures for the mean annual rainfall of a num ber of stations in various parts of the world: It has been proven that rain has a most cleansing effect on the atmosphere, a five days' rainfall in London, England, having carried off not less than 3,738 tons of solid impurities, in cluding 267 tons of sulphate of ammonia, and 2,000 tons of soot and suspended matters.
Rain water would be a chemically pure water but for the variety of impurities which it col lects from the atmosphere in its descent. These include dust, soot, fungi spores, pollen, etc. Rain water also carries a small amount of nitro gen, ammonia, oxygen and carbonic acid gas, and in certain areas, usually over large cities, there are also present minute quantities of nitric acid and sulphuric acid. Rain water thus car ries several of the necessities of plant and animal life to the earth's surface. It becomes safely potable for man only after filtration through the earth's strata, whence it emerges in springs, artesian wells, etc. Until about 1850 scientists supposed rain to be due to the mix ture of cold and warm bodies of moisture-laden air. Espy first propounded the theory that it was due to the cooling of the atmosphere under the expansion of the more heated portions of air. Lord Kelvin and others soon proved this theory correct. When air expands on the with drawal of pressure the work done in expansion is evidenced by a lowered temperature of the expanding air. By convection the warm moisture-laden air ascends and in the course of its ascent is gradually cooled until it reaches the point at which its temperature is the dew point of the original air. Cloud is then formed and if the moisture is abundant the smaller particles coalesce into drops and fall rapidly as rain. If they do not coalesce they may continue to reach higher areas until they become ice particles. The seasonal distribution of rain fall is of greater moment to the agriculturist and stock-raiser than the total annual amount. The ideal, seldom attained, would be an equable division of temperature, rain and sunshine throughout the year. For details of the dis tribution of rainfall throughout continental United States consult Henry, A. J. (Rainfall in the United States> (in Bureau Bulletin D,> Washington, D. C., 1879) ,• (Rain fall and Charts of Rainfall> (in Monday Weather Review, ib., April 1902); and Wallis, B. C. (in Monthly Review, ib., Jan uary, April, June issues 1915).