SPRING, in natural history, a fountain or source of water, rising out of the ground. Various have been the opinions of philosophers concerning the origin of springs; but those which deserve notice are only the three following ones : 1. That the sea water is conveyed through subterraneous ducts, or canals, to the places where the springs flow out of the earth ; but as it is impossible that the water should be thus conveyed to the tops of mountains, since it cannot rise higher than the surface, some have had recourse to subterraneous heats; by which, being rarefied, it is supposed to as cend in vapours through the bowels of the mountains. Hut as no sufficient proof is brought of the existence of these cen tral heats, or of caverns in the mountains big enough to let the vapours ascend, supposing such heats, we shall not take up our reader's time with a formal refu tation of this hypothesis. 2. As to those who advance the capillary hypothesis, or suppose the water to rise from the depths of the sea, through the porous parts of the earth, as it rises in capillary tubes, or through sand or ashes, they seem not to consider one principal property of this kind of tube, or this sort of attraction: for though the water rise to the top of the tube or sand, yet will it rise no higher, because it is by the attraction of the parts above that the fluid rises, and where that is wanting it can rise no further. There fore, thoufh the waters of the sea may be drawn into the substance of the earth by attraction, yet it can never be raised by this means into a cistern, or cavity, to become the source of springs. 3. The third hypothesis that of the sagacious naturalist, Dr. Halley, who supposes the true sources of springs to be melted snow, rain-water, dew, and vapours condensed.
Now in order to prove that the vapours raised by the heat of the sun from the surface of the seas, lakes, and rivers, are abundantly sufficient to supply the springs and rivers with fresh water, the doctor made the following experiment : he took a vessel of water, made of the same degree of saltness with that of the sea, by means of the hydrometer; and having placed a thermometer in it, he brought it, by means of a pan of a coals, to the same degree of heat with that of the air in the ho test summer. He then pla eed this vessel, with the thermometer in it, in one scale, and nicely counterpoised it with weights in the other: after two hours he found that about the sixtieth part of an inch was gone off in vapour, and consequently, in twelve hours, the length of a natural day, one tenth of an inch would have been evaporated. From
this experiment it follows, that every ten square inches of the surface of the water yield a cubic inch of water in vapour per day, every square mile 6,914 tons, and every square degree (or 69 English miles) 33 millions of tons. Now, if we suppose the Mediterranean to be 40 degrees long, and 4 broad at a medium, which is the least that can be supposed, its surface will be 160 square degrees, from whence there will evaporate 5280 millions of tons per day in the summer time. The Me diterranean receives water from the nine great rivers following, viz. the Iberus, the Rhine, the Tiber, the Po, the Danube, the Neister, the Borysthenes, the 'Canals, and the Nile ; all the rest being small, and their water inconsiderable. Now let us suppose that each of these rivers con veys ten times as much water to the sea as the Thames ; which, as is, observed, yields daily, 76,032,000 cubic feet, which is equal to 2U3 millions of tons ; and therefore all the nine rivers will produce 1827 millions of tons ; which is little more than one third of the quantity evaporated each day from the sea. The prodigious quantity of water remaining, the doctor allows to rains, which fall again into the seas, and for the uses of vegetation, &c. As to the manner in which these waters are collected, so as to form reservoirs for the different kinds of springs, it seems to be this : the tops of mountains, in gene. ral, abound with cavities, and subterra neous caverns formed by nature to serve as reservoirs ; and their pointed summits, which seem to pierce the clouds, stop those vapours which fluctuate in the at mosphere, and being constipated thereby, they precipitate in water, and by their gravity easily penetrate through beds of sand and lighter earth, till they are stop ped in their descent by more dense stra ta, as beds of clay, stone, &c. where they form a basin or cavern, and work a pas sage. horizontally, and issue out at the side of the mountain. Many of these springs running down by the vallies, be tween the ridges of hills, and uniting their streams, form rivulets or brooks ; and many of these, again uniting on the plain, become a river.
Springs are either such as run continu ally, called perennial ; or such as run only for a time, and at certain seasons of the year, and therefore called temporary springs. Others again are called inter mitting springs, because they flow and then stop, and flow and stop again : and, finally reciprocating springs, whose wa ters rise and fall, or flow and ebb, by re gular intervals. To account for these differences in springs, see firnastnacs.