serves both as source and as reservoir. Spring water and filtered ground water are used in Frankfurt a. M. for drinking purposes; but for street-sprinkling and manufacturing purposes, etc., water is pumped from the river Main and distributed through a separate system of water pipes. Würzburg uses spring water, but has separate water works for furnishing ground water, from near the river bank, for the Ring parks. Twenty-one cities of the thirtyfive with exhibits in this section use ground water. The source is always near a river; but the water is said to be pure, needing no filtration save when it contains too high a percentage of iron. Augsburg and Darmstadt sink well-shafts into underground streams, and pump the water thus collected to the water-works. Leipzig has to remove the excess of iron. Kiel exhibited a model of the works for removing the iron. The water is caused to trickle over an apparatus through which streams of air are forced. The iron is oxidized and precipitated, and then readily filtered out. Berlin uses filtered river water, mostly. The water is cleared in settling basins, then pumped into the sand filters, from which it is led to the reservoirs. An excellent model on a scale of 1: 50 showed the water-works at the Mügglesee, from which Berlin draws a part of her water. Engines pump the water into a collector, whence it passes to the Enteisenungsanlage ("ironremoving apparatus"). The water is next pumped to the sand filters, where it seeps through a thick layer of fine sand, then through a layer of coarser sand, next through a layer of fine gravel, then through a layer of coarse gravel, and finally through a layer of pebbles, in which are the innumerable opening of pipes through which the water is pumped to the reservoirs. The reservoirs are roofed over with arches of masonry, and covered with turf; so that the heat of the sun does not penetrate in summer, and freezing in winter is avoided. Bremen takes the water of the river Weser, collects it in settling basins, and then pumps it into sand filters, from which it is pumped into the reservoirs. A model exhibited by this city showed how the water may, when occasion demands, be pumped from one filter into another, and so be twice filtered, Breslau likewise derives her water supply from her river, the Oder, and filters it by means of sand filters.

The disadvantages of this system, and the danger of serious contamination, have brought the municipality to realize the need of the use of ground water. Work has been begun, upon an entire new system, with this end in view. Hamburg uses water from the river Elbe, filtered, as above, through sand. Apparently no German municipality is reckless enough to use the contaminated water of a navigable river without first filtering it through sand filters. The impurities are all caught before they have passed through the fine sand, and, indeed most of them settle in a thin layer upon the top. A certain amount of impure matter, filling the interstices between the grains of sand, makes the filter more effective; but an excessive amount impedes the rapid filtration of the water. Hence the necessity for cleaning the filters. Königsberg exhibited a model showing how the top of the layer of sand, containing the impurities, is removed in wheelbarrows, cleaned, and replaced, In this manner twelve men are occupied for eight hours in cleaning each one of the four filters—a surface of about 1,650 square yards (the filters in Hamburg are each about 9,000 square yards in extent).

As in Breslau, so also in Berlin and in Hamburg, the disadvantages of using river water for drinking purposes, especially when it is drawn from rivers devoted to navigation, have been recognized. In both Berlin and Hamburg, therefore, experiments and preparations have been undertaken, looking to the supplying of those cities with ground water.

In the last decades the storing of water, by damming mountain valleys, has commended itself to certain municipalities. Chemnitz, Solingen, and Barmen are examples. Barmen, though for a long time supplied exclusively with spring water, now obtains water from mountain valleys. The natural gravity pressure of the water carries it to the old water-works, where it is filtered. Plauen i. V., at present supplied with spring water from six sources, is planning to erect a dam and filter works in the Geigenbach valley. The water will be distributed, by gravity pressure, through the existing water-pipe system.

Statistics presented by Dortmund-population, 140,000—are

interesting, as they show that, concomitant with a three-fold increase of population in the years 1873-1902, there has been a fifteen-fold increase in the use of water. The necessity for water for manufacturing purposes, for increased domestic use, and for municipal use, is increasing as time progresses.

HOWARD Woodhead.

BERLIN, GERMANY.

[To be continued.]