THE vapour which rises invisibly from the land and water ascends in the atmosphere till it is condensed by the cold into clouds, which restore it again to the earth in the form of rain, hail, and snow; hence, there is probably not a drop of water on the globe that has not been borne on the wings of the wind. Part of this moisture restored to the earth is reabsorbed by the air, part supplies the wants of animal and vegetable life, a portion is carried off by the streams, and the remaining part penetrates through porous soils till it arrives at a stratum impervious to water, where it accumulates in subterranean lakes often of great extent. The mountains receive the greatest portion of the aërial moisture, and, from the many alternations of permeable and impermeable strata they contain, a complete system of reservoirs is formed in them, which, continually overflowing, form perennial springs at different elevations, which unite and run down their sides in incipient rivers. A great portion of the water at these high levels penetrates the earth till it comes to an impermeable stratum below the plains, where it collects in a sheet, and is forced by hydraulic pressure to rise in springs, through cracks in the ground, to the surface. In this manner the water which falls on hills and mountains is carried through highly-inclined strata to great depths, and even below the bed of the ocean, in many parts of which there are springs of fresh water. In boring Artesian wells the water often rushes up with such impetuosity by the hydrostatic pressure as to form jets 40 or 50 feet high. In this operation several successive reservoirs have been met with; at St. Ouen, near Paris, five sheets of water were found; the water in the first four not being good, the operation was continued to a greater depth; it consists merely in boring a hole of small diameter, and lining it with a tube. It rarely happens that water may not be procured in this way; and as the substratum in many parts of deserts is an argillaceous marl, it is probable that Artesian wells might be bored with success. A spring will be intermittent when it issues from an opening in the side of a reservoir fed from above, if the supply be not equal to the waste, for the water will sink below the opening, and the spring will stop till the reservoir is replenished. Few springs give the same quantity of water at all times; they also vary much in the quantity of foreign matter they contain. Mountain-springs are generally very pure, the carbonic acid gas almost always found in them escapes into the atmosphere, and their earthy matter is deposited as they run along, so that river-water from such source is soft, while wells and springs in the plains are hard, and more or less mineral. The water of springs takes its temperature from that of the strata through which it passes: mountain-springs are cold, but, if the water has penetrated deep into the earth, it acquires a temperature depending on that circumstance.