Hydria

“ But the magnitude of a stream is more especially regulated by the extent of country which forms the declivities of its basin, though there is no invariable proportion here, for a small basin in a humid region will yield a greater quantity of water than one much more considerable in a different situation. High mountains, a humid climate, and a wide superficial drainage, are the three physical circumstances which lead to the accumulation of vast bodies of water, the magnitude of which will be proportionate to the degree in which these causes are in combined operation. ”

“ It is indeed the fact that, upon a small area of the earth's surface, yet the most extensive that comes within experience or natural possibility, heavy and continued rain for a few days often produces effects fearfully destructive, by swelling the streams and rivers of that district; but, the laws of nature, as to evaporation and the capacity of atmospheric air to hold water in solution, render such a state of things over the whole globe, not merely improbable, but absolutely impossible. ”

“ Instead of carrying the heat of the air, and of the surface of the ground, to the subsoil, the rain only adds so much to the amount of water to be evaporated, and increases, by so much, the chilling effect of evaporation. ”

“ When, too, in flood time, the hurrying current seems to respond more sensitively to the shape of the shallows and the banks beneath, there boils up from below a ceaseless succession of irregular circles as if the water there expanded from a centre, marking the verge of its outflow with bubbles and raised lines upon the surface. ”

“ For the layer of ice formed, being lighter than water, floats on the surface of the latter, and thus forms a protective layer and prevents to a large extent further freezing, except as a slow thickening of the layer, the total freezing of the water of a lake or river being rendered practically impossible, an obvious provision for the security of life of the piscatorial and other inhabitants of the waters. ”

“ He found that deep drains began to run after wet weather, not from the water above, but from the water rising from subterranean accumulations below, and that by draining the stagnant moisture from three or four feet of earth next the surface, it was rendered more friable and porous, easier to work, and more easily penetrated by the rain. The rain carried down air which, being full of ammonia and manure, made the earth below warmer, and therefore more genial to the roots of the crops. ”

“ Upon every water-shed which is drained into the sea, the precipitation, for the whole extent of the shed so drained, may be considered as greater than the evaporation, by the amount of water which runs off through the rivers into the sea. In this view% all rivers may be regarded as immense rain-gauges, and the volume of water annually discharged by any one, may be taken as an expression of the quantity which is annually evaporated from the sea, carried back by the winds, and precipitated throughout the whole extent of the valley that is drained by it. ”

“ This drains off from the surface, forming rills, which collect as they descend, by their own weight, into the lowest channels of the ground, and form into streams and rivers, and back into the sea comes the water which the air had taken away, with this difference, that it is free from salt and fit for the many uses to which fresh water alone can be applied; when the vapour rises from the sea, none of the saline matters rise with it, for, although the water is volatile, yet they are not, and this is the whole source of fresh water. ”

“ Every considerable addition to its water wells up, and soaks its very surface; and that which is added after it is already brim full, must flow off over the surface, or lie in puddles upon it. Evaporation is a slow process, and it becomes more and more slow as the level of the water recedes from the surface, and is sheltered, by the overlying earth, from the action of sun and wind. ”

“ The hydra is found generally in fresh water, though some few species have been discovered, in this country, in that which is somewhat brackish. It loves still or slowly-running water, and attaches itself generally to the under-side of the leaves or to the stalks of aquatic plants. ”

“ The bulk of the hydræ decreases, in proportion as they extend themselves, and vice versa. They may be made to contract themselves, either by touching them, or agitating the water in which they are contained. They all contract themselves so much when, taken out of the water, as to appear only like a little lump of jelly. ”

“ The warmer the atmosphere, the greater its capacity to hold moisture. The heated, thirsty air of the tropics drinks up the water of the ocean, and bears it away to the colder regions, where, through condensation by cold, it becomes visible as a cloud ”

“ The ground in the neighbourhood is affected by this spring in rather a peculiar manner: at the half-flood tide the pressure is greatest: dry hard clay oozes with great force through openings hardly observable, the silt and water running by starts. At high-water the pressure and quantity of water begin to diminish and on the ebb-tide the ground is hard and dry, and can be worked with ease. ”

“ The proportion borne by the available to the total rainfall varies very much, being affected by the rapidity of the rainfall and the compactness or porosity of the soil, the steepness or flatness of the ground, the nature and quantity of the vegetation upon it, the temperature and moisture of the air, which will affect the rate of evaporation, the existence of artificial drains, and other circumstances. ”

“ In consequence of the effects of mountains in cooling currents of moist air, and causing the condensation of aqueous vapor in the manner above described, it follows that in every country, as a general rule, the more elevated regions become perpetual reservoirs of water, which descends and irrigates the lower valleys and plains. ”

“ Can you imagine these water-particles, just above any pond or lake, rising up and getting entangled among the air-atoms? They are very light, much lighter than the atmosphere; and so, when a great many of them are spread about in the air which lies just over the pond, they make it much lighter than the layer of air above, and so help it to rise, while the heavier layer of air comes down ready to take up more vapour. ”

“ In the second case, the excess of cold by evaporation is withdrawn; the cold water of attraction is removed out of its way; the warm air from the surface, rushing in to supply the place of the water which the drains remove, and the warm summer rains, bearing down with them the temperature which they have acquired from the upper soil, carry a genial heat to its lowest roots. Health, vigorous growth, and early maturity are the natural consequences. ”

“ The temperature of the waters, surface and deep, taken regularly, makes a record for the benefit of those engaged in the propagation of food fishes, which is becoming an important government work. The stage of water taken in connection with the reports of rainfall and temperature of the atmosphere in their influence upon deep beds of snow and ice-locked streams affords ground for warnings, when needed, to persons engaged in any river traffic, or exposed to floods upon the banks. ”

“ Clinging to every tree, stone, or animal tissue is a small quantity of moisture varying with the temperature, the amount of water in the air, and with other well-known factors. It is impossible to rid any natural substance wholly of water without heating it to a high temperature. This water which, apparently, belongs to all natural objects is commonly called hygroscopic water. Hilgard states that the soils of the arid regions contain, under a temperature of 15 deg C. and an atmosphere saturated with water, approximately 5-1/2 per cent of hygroscopic water. ”

“ We have seen, that evaporation proceeds much more rapidly from a surface of water, as a pond or river, than from a land surface, unless it be fully saturated, and that evaporation from the water exceeds the whole amount of rain, about as much as evaporation from the land falls short of the amount of rain. ”

“ The thirteen inches of water are of course supplied by evaporation from the sea, and are carried back to the land through the atmosphere. Vapour is perpetually rising from the ocean, and is condensed in the hills and high lands, and through their pores and crevices descends, till it is deflected, collected, and conducted out to the bay, by some stratum or channel which is watertight. The condensation which takes place in the higher parts of the country, may easily be recognised in the mists and rains which are the frequent occupants of such regions. ”

“ Till then the other rivers run big, from the quantity of rain-water which they bring down from countries where so much moisture falls that all the land is cut into gullies; but in summer, when the showers fail, and the sun attracts their water, they become low. ”

“ Stately and slow that river moves down to the bay, into which it empties its load. The rain that falls on hundreds of square miles of territory flows into the streams that feed this trunk. The little spring that is the headwater of the system is but one of many pockets in the hillsides that hold the water that soaks into the ground and give it out by slow degrees. Surface water after a rain flows quickly into the streams. It is the springs that hold back their supply and keep the rivers from running dry in hot weather. ”

“ But so soon as condensation markedly exceeds evaporation, rain falls, and the atmosphere discharges its vast load of water—how vast we may gather from the fact [Pg 160] that the waters of all the rivers are but a part of the overflowings of the great atmospheric reservoir. "God binds up the waters in his thick cloud, and the cloud is not rent under them." ”

“ The necessary conditions for the formation of extensive salt beds include arid climate and bodies of water which are essentially enclosed—either as lakes, as lagoons, or as arms of the sea with restricted outlets,—where evaporation exceeds the contributions of fresh water from rivers, and where circulation from the sea is insufficient to dilute the water and keep it at the same composition as the sea water. ”

“ Water is no exception. If finely divided, as by placing it in fine capillary tubes, in the pores of wood, or in the narrow spaces of a wick, it may be cooled several degrees below normal freezing-point. In a cloud, or fog, all the conditions necessary for surfusion to take place are undoubtedly present. The water is pure, the envelope is uniform, the subdivision is exceedingly minute, and the drops are free from most of the mechanical disturbances which bring about the solidification of larger masses in the laboratory. ”

“ On the other hand, if the volume of water abstracted is great, its removal deprives its basin of an equalizing and moderating influence; for large bodies of water take very slowly the temperature of the air in contact with their surface, and are almost constantly either sending off heat into the atmosphere or absorbing heat from it. Besides, as we have seen, lakes in elevated positions discharge more or less water by infiltration, and contribute it by the same process to other lakes, to springs, and to rivulets, at lower levels. ”

“ Even if the surface water of a lake or river freezes, or becomes unusually hot, there is generally plenty of water at a lower stratum which maintains a less extreme temperature, and to which creatures can retire on the first symptoms of a change. ”

“ The tide flows up the river many miles past the waterworks, carrying up with it the filth from the sewers. The supply of water was, to be sure, obtained when the tide was down, but as the banks of the river are clothed with sedges in many parts, and its bottom deep with mud, the water can never be free from sewage. ”

“ In arid regions of which the declivities are sufficient to give thorough drainage, the absence of vegetation is accompanied by absence of soil. When a shower falls, nearly all the water runs off from the bare rock, and the little that is absorbed is rapidly reduced by evaporation. ”

“ If we also visit the spot at a time when the river is swollen by heavy rains or melting snows, the presence of this organic matter will be masked by the turbidity of the water; we shall learn that only in the freshet seasons does the water attain sufficient velocity to carry any visible load of sand and clay. ”

“ The consequence of the ancient evaporation, by which the great Pleistocene lake was reduced to its present modest dimensions, and of the ceaseless modern daily evaporation, is the impregnation of the waters of the lake with salts and other mineral substances to a remarkable degree. Ocean water contains on an average 4-6% of salts: Dead Sea water contains 25%. ”

“ If a lake were about to be formed it would be in this way—the rain descending on the surrounding high lands would run in rills to the lowest part, and there collect, forming a pool which would gradually increase in size as the water flowed into it, this increase continuing until the surface became so large that the evaporation from it exactly equalled the supply, it would then extend no further, but remain a permanent lake or inland sea, giving off vapour to refresh the surrounding country, and again receiving it back by streams and rivers, as does the ocean. ”

“ Felling of forests.—The felling of forests has been attended, in many countries, by a diminution of rain, as in Barbadoes and Jamaica.998 For in tropical countries, where the quantity of aqueous vapor in the atmosphere is great, but where, on the other hand, the direct rays of the sun are most powerful, any impediment to the free circulation of air, or any screen which shades the earth from the solar rays, becomes a source of humidity; and wherever dampness and cold have begun to be generated by such causes, the condensation of vapor continues. ”

“ Sludge consists of a stratum of detached ice crystals, or of snow, or of the smaller fragments of brash-ice, floating on the surface of the sea.
A stream is an oblong collection of drift or bay-ice, the pieces of which are continuous. It is called a sea-stream when it is exposed on one side to the ocean, and affords shelter from the sea to whatever is within it. ”