of the oxygen and hydrogen gases, which decompose each other, and produce water; and to the filtering of water from the sea into internal cavities and reservoirs prepared by nature, from whence they make their way to the surface. Some writers contend for the former cause exclusively. Marriotte has examined the point, whether the quantity of rain water is sufficient to feed all the springs and rivers, and so far from finding a deficiency, he concludes upon the amount being so great as to render it difficult to conceive how it is expended. According to experiments which have been made, there falls annually upon the surface of the earth about 19 inches of water, but to render his calculation still more convincing, Marriotte supposes only 15, which makes 45 cubic feet per square toise, and 238,050,000 cubic feet per square league of 2300 toises in each direction. Now the rivers and springs which feed the Seine, before it arrives at the Pont-Royal at Paris, comprehend an extent of territory, about 60 leagues in length, and 50 in breadth, which makes 3000 leagues of superficial area; by which, if 238,050,000 be multiplied, we have for the product 714,150,000,000, for the cubic feet of water which falls, at the lowest estimate, on the above extent of territory. Let us now examine the quantity of water annually furnished by the Seine. The river, above the Pont-Royal, when at its mean height, is 400 feet broad, and 5 deep. When the river is in this state, the velocity of the water is estimated at 100 feet per minute, taking a mean between the velocity at the surface, and that at the bottom. If the product of 400 feet in breadth, by 5 in depth, or 2000 square feet, be multiplied by 100 feet, we shall have 200,000 cubic feet for the quantity of water which passes in a minute through that section of the Seine above the Pont-Royal. The quantity in an hour will be 12,000,000; in a day 288,000,000; and in a year 105,120,000,000 cubic feet. This is not the seventh part of the water which, as previously stated, falls on the extent of country that supplies the Seine, the large remainder, not received by the river, being taken up by evaporation, besides a prodigious quantity employed for the nutrition of plants. A further calculation has been made by the same writer, of the water which ought to be furnished naturally by a spring that issues a little below the summit of Montmartre, and which is fed by an extent of ground 300 toises in length, and 100 in breadth; making a surface of 30,000 square toises. At the rate of 18 inches for the annual quantity of rain, there will fall on that extent an amount equal to 1,620,000 cubic feet. A considerable part of this water, perhaps three-fourths, immediately runs off, so that no more than 405,000 forces its way through the earth and sandy soil, till it meets with a bed of clay at the depth of two or three feet, from which it flows to the mouth of the fountain, and feeds it. If 405,000 therefore be divided by 365, the quotient will be 1100 cubic feet of water, which it ought to furnish daily, or about 38,500 French pints. This makes about twenty-seven pints per minute, which is nearly the produce of the spring.

It appears from this and other calculations, that the rain which falls in particular districts is more than sufficient to account for all their springs and rivers; and some very obvious circumstances show that the origin of springs is almost, if not entirely, owing to the rains which continually moisten the surface of the globe. In seasons of long drought, the greater part decrease in a considerable degree, and some absolutely fail, while they are renewed in the same progression as the descending showers are abundant. It is possibly the case, indeed, that the ocean filtering through pores of the earth-the salt particles being lost in the passage-may give rise to many springs; but as the preceding cause is amply sufficient to explain their formation, we need not recur to any other. The rains and melted snow which the earth absorbs, percolate through crannies, or ooze through the strata, and collect in vast internal reservoirs in mountainous regions, from which the superabundant water finds its way again to the surface, breaking out through fissures in the side and at the bottom of the hills. Copious springs thus issue from the

mountain limestone of England, through the fissures of the rocks, produced in the course of the consolidation and shrinking of the mineral masses. They seldom appear, however, on the sides of limestone hills, but break out in great numbers, and often with extraordinary impetuosity, around their bases. In other conditions of the surface, the water percolates through the masses of sand, gravel, or chalk, that compose it, till it meets the solid rock, or a bed of impervious clay, which arrests its further descent, and springs are then formed at the point of the lowest level, on the edge of the rock or clay that dams it up. With few exceptions, the lower beds of the chalk formation are completely saturated with water which has percolated through the superior strata to the base, where its downward course is stopped by a subsoil of blue clay, which occasions the accumulation in the lower regions of the chalk, and the springs and rivulets which issue near the foot of every chalk hill. It is more difficult to account for springs where the country is neither hilly nor uneven, but constitutes a great level or plain. The water in these instances reaches the surface by ascension, or flows in a direction contrary to that produced by the force of gravitation. There can be little doubt, however, that many of these springs derive their supply from distant elevations, and are produced by the natural tendency of liquids to find their level. Other examples are perhaps due to capillary attraction, in consequence of which water ascends through the pores of the earth in the same manner as it rises in capillary tubes-in sponge or sugar-loaf - so long as the latter remains undissolved. In order to give a distinct though general view of the curious and complicated phenomena of springs, they may be advantageously considered under different heads.

St. Winifred's Well.

1. Perennial. Some springs are ever-flowing, and answer to the expression of sacred poetry-the "fountains of living water." They do not dry up during the longestcontinued drought, and suffer little or no diminution in their volume. These are obviously quite independent of the last showers that have fallen, though their supply may primarily proceed from the rain and melted snow. It is reasonable to suppose that they gush from a body of water collected in subterranean cavities, so vast as not to be drained off by the constant stream during the most protracted season of dry weather, before the interior basin is replenished. Of this nature is the celebrated spring of St. Winifred, at Holywell, in Flintshire, one of the finest in the world, which appears to be situate at the point where the limestone first comes in contact with the coal measures. The quantity of water thrown up

is estimated at eighty-four hogsheads, or twenty-one tons, in a minute. It has never been known to fail, but is subject to reduction during drought. The stream never

freezes; and though its course is little more than a mile before it arrives at the sea, yet eleven mills are put in motion by it. The spring issues from the rock into a beautiful polygonal well, over which the Stanley family erected a chapel about the time of Henry VII. Upon the windows the chief events of St. Winifred's life are painted. The saint is reported to have been a virgin martyr who suffered upon this spot, the spring miraculously rising from her blood; and hence the veneration for the well in popish times. Pennant says of his own time: "The custom of visiting this well in pilgrimage, and offering up devotions there, is not yet entirely set aside. In the summer a few are still to be seen in the water, in deep devotion, up to their chins for hours, sending up their prayers, or performing a number of evolutions round the polygonal well. In the year 1686 James II. visited this well, and received as a reward a present of the very shift in which his great grandmother, Mary Queen of Scots, lost her head." There are springs similarly powerful along the confines of the limestone district, which vary very little in their quantity of water, either in drought, or after the heaviest rains. About Denton, in Yorkshire, the roaring of the waters is incessant.

2. Intermittent. Many springs gush with vehemence, then subside, shrink away, and disappear, renewing their tide in its full strength at irregular intervals. They clearly derive their supply from the last rains, and hence fail altogether in dry seasons. On the chalk downs of the south of England, in Wilts and Dorset, it is a very common circumstance for the valleys to be quite dry in one part of the year, and very fully watered in another; and hence a Wiltshire proverb says,

"As the days lengthen, the springs strengthen."

But we may suppose such a cavity in a hill as A in the diagram, a reservoir fed by rain percolating through the superior rocks, and communicating with the surface by an arched channel, like BC D. As long as the water in the cavity is above the level of the channel

at C, it will escape through it, and gush out at D; but the spring will cease when the water of the interior basin has been reduced to that level, and not be renewed until it rises above it. The flow of the spring will also be more impetuous in proportion as the water of the cavity accumulates above the vertex of the siphon-formed arch. This is the principle of the Artesian wells, which have been constructed with signal success near many large cities occupying level sites, and formerly inconvenienced by the want of natural springs, or by the

bad quality of the surface water. The action of these wells, puits Artésiens-so named from the province of Artois, where they have been long in use-is due to the constant endeavour of liquids to find their level. If we suppose a basin-shaped country, or a plain enclosed with heights, the rain which falls on the circumjacent hills being absorbed among the rocks, may be conducted through one of the underlying strata of the plain, completely occupying it, and yet be prevented from sinking lower, and also from reaching the surface, by inferior and superincumbent beds of solid rock or impervious clay. In such circumstances a perpendicular perforation or boring into the ground is made, penetrating the superior impervious bed, and reaching the saturated stratum through which the water rises to the surface. Thus suppose a town situated upon a bed of clay

or mass of rock impervious to water, as AA; B B a stratum through which it readily circulates, and which crops out or rises from beneath A A on each side; cc also a rock through which it cannot pass. It is clear that rain, falling on the permeable stratum where it crops out, and being absorbed by it, yet prevented from passing downward under the action of gravity by the rock c c, will travel laterally through the stratum under the town, unable however to find its level, and force its way to the surface through the superincumbent rock a a. This is a condition in which an artificial boring at w, through A A to B B, will

Artesian Well.

C

liberate the water of the latter, which will rise in the vent to the surface of the plain, in proportion as its source is elevated above it. Artesian wells, notwithstanding their modern name and its local derivation, appear to have been well known in various countries and in ancient times, without perhaps any apprehension of their principle. Neibuhr quotes an ancient writer as saying, "Wells are sunk in the oases from two to four hundred yards in depth (the yard in question being equal to half a foot), whence water rises and flows over."

3. Reciprocating. There are springs which exhibit phenomena analogous to the flux and reflux of the tides of the ocean, some at regular intervals during the day, and others at more distant and uncertain periods. In one of the two letters addressed by the younger Pliny to Licinius, he describes a spring of this kind by the Larian lake-the modern Lake of Como :- "I have brought you," he remarked, "as a present, out of the country, a query which well deserves the consideration of your extensive knowledge. There is a spring which rises in a neighbouring mountain, and, running among the rocks, is received into a little banqueting room, from whence, after the force of its current is a little restrained, it falls into the Larian lake. The nature of this spring is extremely surprising; it ebbs and flows regularly three times a day. The increase and decrease is plainly visible and very amusing to observers. You sit down by the side of the fountain; and whilst you are taking a repast, and drinking its water, which is extremely cool, you see it gradually rise and fall. If you place a ring or any thing else at the bottom when it is dry, the stream reaches it by degrees till it is entirely covered, and then gently retires; and if you wait you may see it thus alternately advance and recede three successive times. Shall we say that some secret current of air stops and opens the fountainhead as it approaches to or retires from it, as we see in bottles, and other vessels of that nature, when there is not a free and open passage; though you turn their necks downwards, yet, the outward air obstructing the vent, they discharge their contents as it were by starts? But may it not be accounted for upon the same principle as the flux and reflux of the sea? Or as those rivers which discharge themselves into the sea, meeting with contrary winds and the swell of the ocean, are forced back into their channels, so may there not be something that checks this fountain, for a time, in its progress? Or is there rather a certain reservoir that contains these waters in the bowels of the earth, which, while it is recruiting its discharges, the stream flows more slowly and in less quantity; but, when it has collected its due measure, it runs again in its usual strength and fulness? Or, lastly, is there I know not what kind of subterraneous counterpoise, that throws up the water when the fountain is dry, and stops it when it is full? You, who are so well qualified for the enquiry, will examine the reasons of this wonderful phenomenon: it will be sufficient for me, if I have given you a clear description of it. Farewell."

The fact of the flow and ebb was reported, in antiquity, of a fountain, the celebrity of which is co-extensive with the prevalence of Christianity itself:—

"Siloa's brook that flow'd

Fast by the oracle of God."

The pool of Siloam is a reservoir of artificial construction, fifty-three feet long by eighteen broad, into which a small stream flows, and is led off to irrigate the gardens of fig and fruit trees that lie along the slope of the Valley of Jehoshaphat. The stream enters the pool through a subterranean channel cut in the solid rock, and comes from the fountain of the Virgin, higher up in the valley. The irregular flow of the water is first distinctly mentioned by Jerome in one of his Commentaries, towards the close of the fourth century, who remarks: :"Siloam is a fountain at the foot of Mount Zion, whose waters do not flow regularly, but on certain days and hours, and issue with a great noise from hollows and caverns in the hardest rock." An earlier record in the same century- that of a still extant Itinerary from Bourdeaux to Jerusalem— magnifies this circumstance into a flowing for six days and nights, and a resting on the seventh day; an ancient popular legend, which might originate the statement of the elder Pliny, of there being a river in Judea that dries up on the sabbath day. The popular belief is still firm among the inhabitants of Jerusalem, respecting the flow and ebb of the water; but most modern travellers seem to have regarded it as an idle story, till Dr. Robinson was enabled to establish its truth. He has given the following account of the event:-"Having been, very unexpectedly, witnesses of the phenomenon in question, we are enabled to rescue another ancient historical fact from the long oblivion, or rather discredit, into which it has fallen for so many centuries. As we were preparing to measure the basin of the upper fountain (in the afternoon of April 30th), and explore the passage leading from it, my companion was standing on the lower step near the water, with one foot on the step and the other on a loose stone lying in the basin. All at once he perceived the water coming into his shoe; and, supposing the stone had rolled, he withdrew his foot to the step, which, however, was also now covered with water. This instantly excited our curiosity; and we now perceived the water rapidly bubbling up from under the lower step. In less than five minutes it had risen in the basin nearly or quite a foot; and we could hear it gurgling off through the interior passage. In ten minutes more it had ceased to flow; and the water in the basin was again reduced to its former level. Thrusting my staff in under the lower step, whence the water appeared to come, I found that there was here a large hollow space; but no further examination could be made without removing the steps. Meanwhile a woman of Kefr Selwân came to wash at the fountain. She was accustomed to frequent the place every day; and from her we learned that the flowing of the water occurs at irregular intervals; sometimes two or three times a day, and sometimes, in summer, once in two or three days. She said, she had seen the fountain dry, and men and flocks, dependent upon it, gathered around and suffering from thirst; when all at once the water would begin to boil up from under the steps, and (as she said) from the bottom in the interior part, and flow off in a copious stream. In order to account for this irregularity, the common people say "that a great dragon lies within