Hygiene and public health / by B. Arthur Whitelegge.

  • Arthur Whitelegge
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: Hygiene and public health / by B. Arthur Whitelegge. Source: Wellcome Collection.

    158/610 (page 146)
    affected by rainfa]], or rather by that portion of the rainfall which percolates through the soil; also by the height of water in adjoining streams or seas, and other conditions modifying the facility of outflow—artificial drainage, for example.^ Sometimes the range of rise and fall does not exceed a few inches, but it is more usually several feet. Above the level of the ground-water the soil, though aerated, is still kept moist by capillary attrac- tion, by evaporation from below, by rainfall, and by the movements of the ground-water. The soil con- stantly loses moisture by evaporation from the surface, both directly and through vegetation. The moisture of a sample of soil is estimated by weighing it before (b) and after (a) drying it on a water-bath. Then ^—~ x 100 = percentage weight of water in sample. The level of the subsoil water is necessarily that of the water in surface wells, and may be gauged by lowering into the well a cord or rod bearing little cups at short intervals, or more simply by means of an index connected by a cord with a float. When the ground-water rises, it forces air out of the soil, and at the same time may pollute wells by bringing into them the washings of im- pure soil. As the ground-water falls again it leaves the soil moist and aerated, conditions favourable for fermentative and putrefactive processes in polluted soil. Damp ground is rendered dry, and the level of its ground-water permanently lowered, by subsoil drainage. For this purpose ^' agricultural pipes, i.e. unglazed porous pipes, are laid loosely end to end at the bottom of deep trenches, and covered in. The interval to be * De Chaumont found tlie tide affecting the level of a well 140 feet above ntiean water level, at a distance of 2,240 feet.