SPRING 



SPRING-BALANCE 



561 



from the surface of the earth, and, reabsorbed 

 by the atmosphere, is employed by plants and 

 animals. All loose soils and gravels greedily absorb 

 water, which descends until it meets with a stratum 

 through which it cannot penetrate. A pit dug into 

 the water-charged soil would speedily till itself by 

 draining the water from the soil. All rocks con- 

 tain water ; some retain it by capillary attraction, 

 like a sponge, others hold it merely mechanically, 

 and easily part with it. Chalk will absorb and 

 retain one-ttiird of its bulk of water ; and sand, on 

 the other hand, while it will absorb as much, will 

 part with nearly the whole amount to a well dug 

 in it. Argillaceous deposits and compact rocks are 

 barriers to the passage of water, and cause the 

 superincumbent pervious strata to become water- 

 logged when there is no outlet. Sometimes the 

 edges of the strata are exposed on the sides of a 

 valley, and permit the free escape of the contained 

 water, which pours from them over the neighbour- 

 ing land. But rente and fissures, as well as 

 inequalities on the surface of the impervious beds, 

 give the water a circumscribed course, and cause 

 it to issue in springs. 



The water, as it percolates through the earth, 

 always becomes more or less charged with foreign 

 matter, owing to its solvent property. Carbonate, 

 sulphate, and muriate of lime, muriate of soda, and 

 iron are the most common impurities in spring- 

 waters ; magnesia and silica also frequently occur. 

 These substances, from the evaporation of 'part of 

 the water, or the escape of the carbonic acid gas, 

 by which so large a quantity is often held in solu- 

 tion, are frequently deposited on the margins of the 

 springs, or in the courses of the streams flowing 

 from them. Such deposits are found in all so-called 

 petrifying springs ; and the hot wells of Iceland, 

 the Yellowstone Park, and the Azores are sur- 

 rounded with basins formed of siliceous sinter which 

 has been derived from the water. When the foreign 

 ingredients have medicinal qualities the springs are 

 known as Mineral Waters (q.v.). 



Springs are either associated with the superficial 

 strata or rise from a considerable depth. Surface- 

 springs occur where the absorbent surface-deposits 

 rest on an impervious bed, which prevents the 



Fig. 1. 



further downward progress of the water, or where 

 the beds through which the water flows are near 

 the surface, as shown in fig. 1, where C and E are 

 impervious day-lie.!.-, ana D is a bed of sand or 

 gravel, which in the upper portion is exposed on 

 the surface, or is only overlaid by loose soil, and 

 after being covered for some distance by the clay- 

 bed, C, makes its appearance again at B, where the 

 valley cuts it through : here the water collected 

 over the area, A, is discharged. Surface-springs, 

 depending as they do so directly on the rain for 

 supplies, are very variable in the amount of water 

 they deliver. They frequently fail entirely in the 

 Hiiinmer, and always after great droughts. Their 

 temperature varies "with that of the district where 

 they exist, being warm in summer and cold in 

 winter, as they do not penetrate below that plane 

 in the earth's crust which is affected by the seasonal 

 changes in temperature. 



When the bed which forms the reservoir for the 

 spring is at such a distance from the surface as to 



be beyond the zone of season changes, and yet 

 within that which is influenced by the climate, 

 the water has a temperature equal to the mean 

 temperature of the locality where it springs. Such 

 springs have generally a large area for the collec- 

 tion of the superficial water, and are consequently 

 regular in the quantity of water they give out. 

 They are brought to the surface by means of 

 master-joints and dislocations. The celebrated 

 Well of St Winifred at Holywell, in Flintshire, 

 rises through a fault in the coal-measures. It 

 formerly discharged about 4400 gallons per minute, 

 and the >yater, in its short course of little more 

 than a mile to the sea, was used to propel eleven 

 mills ; but the discharge has been much diminished j 

 by drainage works. 



Most deep wells have a lower origin than the 

 zone of climate temperature, which in Britain is 

 between 200 and 300 feet. It is well known that 

 a regular increase in the temperature is observed 

 after this zone is passed, equal to 1 of F. for every 

 54 feet. As wells have a temperature correspond- 

 ing to that of the strata from which they spring, it 

 follows that the deeper the spring the higlier will 

 be its temperature. Local conditions may affect 

 the thermal state of springs, as in the case of the 

 geysers in the active volcanic district in Iceland, 

 and the warm springs near Naples ; but where no 

 such local influences exist the depth of the bed 

 from which the water comes may be to some extent 

 estimated by its temperature. Thermal springs 

 occur in Britain at Matlock (66 F.) and Buxton 

 (82) in Derbyshire, at Bath (117) in Somerset, 

 and at Clifton ( 76 ) in Gloucestershire. Artificial 

 communications have been opened with deep-lying 

 strata, by which the water they contain has been 

 brought to the surface, and in these the tempera- 

 ture is found to increase in proportion to the depth 

 of the bore (see ARTESIAN WELLS). The most 

 remarkable thermal springs are the geysers of Ice- 

 land and the Yellowstone Park (see GEYSER, 

 YELLOWSTONE PARK). 



Intermittent springs are sometimes produced by 

 the ebb and flow of the tide, as at Richmond, where 

 the rise at high-water is seen in the wells which 

 flow from the arenaceous strata on the banks of the 

 Thames ; and sometimes they depend on the supply 

 of rain-water. But there is a kind of spring the 

 intermittences of which are believed to oe owing 

 to the structure of the internal cavities from which 

 the supply is obtained. This will be more easily 

 understood by a reference to the accompanying 

 diagram ( fig. 2 ). The large reservoir, A, is fed by 

 the rain percolating through the rock. It com- 

 municates with the surface by a siphon-shaped 

 tube, BCD. As long as the water in the reservoir 



Fig. 2. 



is at a lower level than the arch of the siphon at 

 C no water can escape ; but as soon as it reaches 

 its level the whole of the water in the cavity 

 will be drawn off, the spring will then cease, and 

 will only make its appearance when sufficient 

 water has accumulated to permit the siphon again 

 to act. 



Spring-balance. See BALANCE. 



