the rain, the pressure will always be in proportion to its perpendicular height, and not to its length, if it wind. The same process in nature may produce the most extensive devastation; it may cause earthquakes, and split or heave up mountains. Suppose, in the bowels of some mountain, there should be an empty space of ten yards square, and only an inch deep on an average, in which a thin layer of water had lodged so as to fill it entirely; and suppose, that, in the course of time, a small crack of no more than an inch in diameter should be worn from above two hundred feet down to the layer of water; if the rain were to fill this crack, the mountain would be shaken, perhaps rent in pieces with the greatest violence, being blown up with a force equal to the pressure of above 5022 tons of water, though not above a ton and a half altogether had been actually applied. The same thing would happen if any one on the spot where there' is such a layer of water below ground, should bore down in sinking a well, or seeking for a spring and then fill the tube with water; it is impossible to fix the limits to the convulsion which might ensue. This prodigious power however may be employed safely, and even beneficially. In the operations of nature, it is probably an important agent, though it has not been sufficiently attended to by philosophers in their attempts to explain natural appearances; and it is capable of being applied advantageously in the operations of art. It may plainly be used with great effect in mining. On a smaller scale, and as a power in machinery, it may certainly be employed far more extensively than it has hitherto been. A tube of a yard long, acting on a cavity of of a yard square, will give a pressure equal to the weight of three quarters of a ton avoirdupois, if used with water; but quicksilver may be employed instead of water, and as it is between thirteen and fourteen times heavier, we shall have a power of ten tons, by the use of a tube and a few pounds of mercury; and in like manner the power of a ton weight may be obtained within the space of a square foot in breadth, by a tube a little less than three feet long, and of the bore of a common goose quill.

INTERMITTING SPRINGS.

The strange appearance of intermitting springs, or springs which run for a time, and then stop altogether, after a time run again, and then stop, is entirely occasioned by the channels in which the water flows being formed like syphons. Thus if ABC (see cut,) represent a hill or mountain, in which there is a hollow E FG, and a channel bent like a syphon F H B leading

the level of F. It will then cease to flow until the hollow is again filled to the level O P, when it will flow again, and so on. Some springs, called variable, or reciprocating, do not cease to flow, but only discharge a much smaller quantity of water for a certain time, and then give out a greater quantity. This is owing to the hollow being supplied from another hollow, which is situated higher up, and has a common runner going to join the stream below the bend H; for this runner keeps the stream always supplied to a certain degree, and when the lower hollow, which feeds the syphon runner, F H, is filled up to OH, both the common runner and the syphon runner feed the stream together, until the lower hollow be drained.

In some places the most absurd tales are told, and believed by ignorant people, respecting such springs; their flowing and ceasing are ascribed to witchcraft; and designing men have sometimes taken advantage of the credulity of others, and gained credit for themselves, by foretelling the return of the spring after it had ceased, or pretending to stop it when it was running. Some notions connected with superstitions of this kind are adverted to in the account given of an intermitting, or rather a variable spring, at Laywell, near Torbay, in Devonshire, by Dr. Atwell, the first person who distinctly explained these appearances by the nature of the syphon. It is a long mile (says he) distant from the sea, upon the north side of a ridge of hills, lying between it and the sea, and making a turn or angle near this spring. It is situated in the side of those hills, near the bottom, and seems to have its course from the S.W. towards the N. E. There is a constantly running stream which discharges itself near one corner, into a basin, about eight feet in length, and four feet and a half in breadth, the outlet of which is at the furthest end from the entrance of the stream, about three feet wide, and of a sufficient height. This I mention, that a better judgment may be made of the perpendicular rise of the water in the basin at the time of the flux or increase of the stream. Upon the outside of the basin

are three other springs, which always run, but with streams subject to a like regular increase and decrease with the former; they seem, indeed, only branches of the former, or rather channels discharging some parts of the constantly running water, which could not empty itself all into the basin; and, therefore, when, by means of the season, or weather, springs are large and high, upon the flux or increase of this fountain, several other little springs are said to break forth, both at the bottom of the basin and without it, which disappear again upon the ebb or decrease of the fountain. All the constant running streams put together, at the time I saw them, were, I believe, more than sufficient to drive an overshot mill, and the stream running into the basin might be one half of the whole. I had made a journey, purposely to see it, in company with a friend; when we came to the fountain, we were informed by a man, working just by the basin, that the spring had flowed and ebbed about twenty times that morning, but had ceased doing so about half an hour before we came. I observed the stream running in the basin for more than an hour, by my watch, without perceiving the least variation in it, or the least alteration in the height of the surface of the water in the basin; which we could observe with great nicety, by means of a broad stone laid in a shelving position in the water. Thus disappointed, we were obliged to go and take some little refreshment at our inn, after which we intended to come back and spend the rest of our time by the fountain, before we returned home. They told us in the house, that many had been disappointed in this manner and the common people superstitiously imputed it to I know not what influence which the presence of some people had over the fountain; for which reason they advised, that, in case it did not flow and ebb when we were both present, one of us should absent himself, to try whether it would do so in the presence of the other. Upon our return to it, the man, who was still at work, told us that it had begun to flow and ebb about half an hour after we went away, and hai done so ter or twelve times in less than

a minute. We saw the stream coming into the basin, and likewise the others on the outside of the basin begin to increase, and to flow with great violence, upon which the surface of the water in the basin rose an inch

and a quarter perpendicularly, in near the space of two minutes; immediately after which, the stream began to abate again to its ordinary course, and in near two minutes time the surface was sunk down to its usual height, where it remained two minutes more; then it began to flow again as before, and in the space of twenty-six minutes, flowed and ebbed five times; so that an increase, decrease, and pause, taken together, were made in about five minutes, or a little more. could observe, by the mark upon the stones, that the surface of the water in the basin had risen before we came, at least three-quarters of an inch perpendicularly higher than we saw it; and I thought that I could per'ceive some very little abatement each turn, both in the height, and in the time of its sinking; but the time of the pause, or standing on the surface at its usual height, or equable running of the stream, was lengthened, yet so as to leave some abatement in the time of the rising, sinking, and pause taken together."-(Phil. Trans. No. 424.)

It should seem that, in the hill from which this stream comes, there are three hollows, or reservoirs, of different sizes, and connected by syphons of different widths. The times of the increase and decrease lengthening, arises from the water sinking in one of the reservoirs, which makes it flow more slowly than when it is full.

In some places there are springs which run freely in summer, or in dry weather, and almost stop in winter, or in wet weather. This is owing to a hollow in the hill being fed by runners, but having, beside the vent through which the spring flows out, a waste pipe, formed higher up, like a syphon, which carries off all the water another way as soon as the space is filled high enough. Thus, while the water is low in dry weather, this waste pipe does not act, and the water flows out through the spring; but as soon as the rains