&achy-his in his 'Eumenides) speaking through Athena said: Meow briPltollted fhPdeon frisk* 'mow, okra" eiv+sett- for4v, wind' has been translated as follows : VMS if limb grams &dad and tainted soil Omar ruftr arsni pollute, no drink thnult end." thin 'yarning the Athenians of the dangers in polluted water.
recommended that drinking water filtered and boiled before using it. That is some proof that he realized that raw aver ought to he sterilized before it was drunk. The Romans knew that some waters were Im mutable for drinking purposes and used their poorer qualities for irrigation, municipal foun tains and other public non-potable purposes. Not until the advancement of science in the 19th century had revealed waterborne diseases, did the quality of the water supplies of com munities arouse_ public attention.
The Germ Theory of Disease,—The mod ern sciences of and biology re vealed the nature and activities of myriads of microscopic organisms in impure water herein before partially described and how they become the media of infection and the agencies for spreading diseases. After the discoveries of Theodor Schwann, Louis Pasteur, Robert Koch, Ferdinand J. Cohn, Joseph Lister and others during the last century • the germ theory of disease' was generally accepted. Those pathologists turned their attention to the discovery of means of combating the active agencies that were destructive of human life. They made several important discoveries of antitoxins, serums and lymph, of inesti mable pathological utility to the race. These, however, were insufficient to check the ravages of all infectious diseases, some of which, as was stated, are 4ransmittcd through living organisms in potable waters. That led to the study of the water supplies of communities, case of the most engrossing subjects of the last and present century. Municipalities and communities generally for their own welfare must consider and solve this problem regard less of the expense thereby entailed upon tax payers, for it is growing in importance in many habitable parts of the globe with the elm-increasing density of population. Before entering upon the study of the processes for the purification of water supplies, it may be well to consider some of the physical conditions that contribute to the production of the abund ant waters, found in the habitable portions of the earth.
Earth's Water Supply.—Three-fourths of its surface is covered with salt water and from those inexhaustible fountains of the deep the host of the sus is continually drawing invisible vapor up into the strata of the atmosphere, wrote the aqueous vapor is cooled and becomes visible and is wafted landward over continents. It comes in contact with hills and mountain ranges and is precipitated in rain and snow and so replenishes the infinite watersources of the uplands of the earth. Whether in some
one of its varied forms. it accumulate in in atrugnmtable s of snow, giving mountain their names as it did the Himalayas, or in another form it become rivers of ice, like Alpine glaciers to form such commerce-bear ing rivers as the Rhone, or in another form it roll in ceaseless tidal billows encircling the globe, or still in another form it float in vaporous clouds landward to fall in refreshing rains over vast areas of territory to percolate the soil and be stored in an infinite number of natural reservoirs, whence it flows in countless streams to nourish the fruits of the earth and supply the wants of man, it conditions and largely controls the activities of every genera tion and will continue so to do fur all time.
Next to the free air we breathe, water is man's greatest earthly possession. Water is freely showered upon the earth in abundance and is stored up in countless pools, _ponds, ground waters, subterranean springs and other natural reservoirs and is accumulated in brooks, creeks, streams, rivers, lakes, sounds, bays, seas and the oceans, covering three-fourths of the earth's surface and making habitable a large part of the remaining fourth. Its dis tribution is affected by the uplift and physical configuration of continents and their relation to oceans, the rotation of the earth upon its axis, the temperature, humidity, succession and varying seasons, climate and trade and other prevailing winds. All of these and other natural phenomena more or less condition the amount of precipitation over different areas. Some lofty mountain ranges, continually inter cepting vaporous clouds swept inland from the oceans and seas, arc capped with permanent masses of snow, which arc unfailing sources of water supply for great rivers like the Amazon, the Yukon, the Rhone, the Ganges and others. Other mountain ranges cause al most daily precipitation in the form of rain, which collects in innumerable natural basins on the surface and below it, but high above the sea-levet. These are the source of mountain streams and of the occasional underground flow found in some mountain regions. The amount of precipitation varies over different areas. In the polar regions there is nu ram and all precipitation there is congealed in the form of snow and icy particles. Rainfall or precipitation is quite fully treated in the special article under the title, RAINFALL, in Volume 23 of this Encyclopedia, to which reference is herein made for the amount thereof over various areas of the habitable globe.