The editors of the abridgement proceed to give a long account of Mr. Atwell's explanation of this system: but as the reader will find a much easier and simpler illustration by Mr. Gough in the ensuing sub-section, it is unnecessary to quote it in the present place. EDITOR. 5. Giggleswick Well. A description of this fountain has been given by several visitors, but far better by Mr. Gough in the Memoirs of the Transactions of the Manchester Society than by any other writer we are acquainted with. This gentleman first briefly examines the nature and history of the more curious periodical springs that have been observed and described, and particularly those of Como, Dodona, and Paderborn, which he ascribes to the principle of a siphon; and then by way of explaining this principle and of developing the well in question proceeds as follows: This instrument consists of a vessel furnished with a siphon, છે. upon the principle of siphons. "Mr.Atwell," says the writers of the recent Abridgment, comes now to his hypothesis, for explaining the phænomena observed; and he imagines them to be occasioned by two streams or springs, one of which passing through two caverns or natural reservoirs with siphons, meets with the other stream in a third reservoir, without a siphon; where being joined, they come out of the earth together. The petitio principii, or supposition of reservoirs and siphons in the bowels of the earth, has been made by others: Pére Regnault, in his Phil. Conversations, Vol. ii. Conv. 6, p. 125, &c. Eng. edit. has mentioned it in general; and Dr. Desaguliers, in Phil. Trans. No. 384, has attempted to apply it to two cases in particular; as Dechales, Tract, xvii. de Fontibus Naturabilis, &c. prop. xv. had done in two other cases before him. It is indeed unnatural, or hard to be granted. Whoever has seen the Peak of Derbyshire, the hilly parts of Wales, or other countries, must be satisfied that they abound with caverns of many sorts. Some of them are dry, others serve only for passages, or channels, to streams, which run through them; and a third sort collect and hold water, till they are full. They must also have observed, that there are sometimes narrow passages, running between the rocks which compose the sides, and going from one cavern to another. Such a passage, of whatever shape or dimensions, how crooked and winding soever in its course, if it be but tight, and runs from the lower part of the cavern, first upwards to a less height than that of the cavern, and then downwards below the mouth of the said passage, will be a natural siphon. which may be attached to it in different ways. To avoid the necessity of a diagram, we will suppose the bottom of the vessel to be perforated, and the longer leg of the siphon to pass through the hole, being firmly cemented in a position, which places the highest point of the bend within the vessel, and half an inch or an inch below the brim, and at the same time keeps the open or lower end of the shorter leg at a small distance from the cup's bottom. Water flows through a tube in an uniform stream into the cup; where it is collected for want of egress, and entering the siphon at the open end of the shorter leg, it rises gradually to the bend or highest point. The subsequent rise of the water in the cup, forces the column in the ascending leg of the siphon, to pass over into the descending or longer branch; upon which this instrument begins to act, not in the manner of a simple tube, but in its proper character. Now the draft of the siphon is made to exceed the opposite stream or supply of water; in consequence of which contrivance the cup is emptied again sooner or later; at this moment the action of the siphon is suspended, until the cup is replenished by the constant current. In this manner the water will be seen rising and falling alternately in the cup, which will be full and empty, or nearly so, by turns. Similar vicissitudes will also take place in the siphon; for it will run so long as its shorter leg is in the water, and then stop, until the highest point of the bend is again covered by the contents of the cup. The transition is easily made from Tantalus's cup to a fountain, which reciprocates periodically; for we have only to suppose a secret reservoir to be formed in the bowels of a mountain on the principles of this instrument, and the following appearances will take place in the visible well, which receives the water from the natural siphon. Ist. So soon as the surface of the pool in the subterranean reservoir, rises above the bend of the siphon, this canal will begin to act; and its discharge will be greater at that moment than at any other period; because the power of a siphon is greatest, when the distance, betwixt the bend and the surface of the water in the basin, is least. 2d. This abundant influx into the external well will make it rise; in consequence of which the efflux will continue to increase at the outlet, so long as the water continues to accumulate in the visible basin. 3d. Now the discharge from the outlet, which be. comes more copious every moment, being contrary to the influx from the siphon, which grows gradually weaker, the surface of the well will cease to rise so soon as these opposite powers are equal in their effects; and the flow will be at the full in this instant. 4th. The well cannot remain stationary, for any length of time, at its highest elevation; because the vigor of the siphon being perpetually on the decline, all the water discharged by it will run off through the outlet, together with part of that, which had been previously accumulated in the visible fountain, during the time of the flow. 5th. Hence it is evident that the well will begin to subside, the moment it becomes stationary; after which it will persevere in a retrograde motion, until the siphon shall have emptied the subterranean reservoir. 6th. If no veins of water discharge themselves into the visible basin, besides the siphon which runs periodically, the spring is called an intermitting fountain. The Bolderborn is of this kind, for it remains dry while the secret reservoir is filling, and flows while the siphon is in action. 7th. But if the spring receives other supplies in addition to the intermitting current, it is called a reciprocating fountain; because the stream that issues from the outlet of the visible basin is permanent, though it varies in quantity; on this account the well ebbs and flows alternately, but never runs itself dry. All the fountains, which will be mentioned in the sequel are of this kind; and Pliny's well, near Coma, appears to possess the same character from his description of it. 8th. The fluctuations of an ebbing and flowing well, which is fed by a siphon, will remain invariable, so long as the stream, that falls into the subterranean reservoir continues to be uniform. But these external and visible operations of the well, are so far under the influence of the current last mentioned, that they will evidently suffer a temporary suspension, so often as the influx into the concealed cistern, amounts to a certain quantity in a certain time; for the siphon is but a second. ary agent in producing the phenomena of reciprocation, its business being to empty the subterranean basin, so often as it is replenished. Now the time of filling this magazine of water will be the shortest, when the influx into it is most abundant, and the contrary; consequently an increased discharge into the subterranean reservoir, will diminish the intervals of the siphon's inactivity, and prolong the periods of its action. It follows, from these premises, that when the influx becomes equal to the feeblest effort of the siphon, the quantity of water thrown into the concealed basin, will exactly counterbalance the quantity which is drawn off by the crooked canal; and the external well will assume the character of a common fountain under these circumstances. I have now explained the principles, on which the common theory of reciprocating springs is founded; and the necessary consequences of the theory are stated in the eight preceding propositions. This has been done, to shew with what ease a natural apparatus on the construction of Tantalus's cup elucidates the appearances, which have been ascribed by writers to the fountains of Dodona, Coma, and Paderborn. The operations of these springs are happily illustrated by the instrument in question; on which account I do not hesitate to pronounce the theory to be a good one, so far as it relates to these fountains alone; provided they are faithfully described. The simplicity of the preceding explanation, and its coincidence with the narratives of the two Plinys, as well as the history of the inconstant brook in Westphalia, disposed me to admit the common theory, and to imagine it to be equally applicable to reciprocating fountains in general; until an instance occurred to my notice, which proved that, fluctuating fountains, do not universally exhibit the periodical operations which are described by the writers already quoted. I made a visit to Giggleswick Well, in the autumn of 1796; which taught me to value this once favourite theory not so highly, and in particular to dispute the universality of its application. The causes of these doubts will be easily perceived from the following description of the well and its operations. This spring lies at the foot of Giggleswick Scar, which is a hill of limestone in the West Riding of Yorkshire. The water discharged by it, falls immediately into a stone trough; in the front of which are two holes near the bottom; these are the outlets of two streams, that flow constantly from the artificial cistern. An oblong notch is also cut in the same side of the trough; which extends from the brim of it, nearly to the level of the two holes already mentioned. This aperture is intended to shew the fluctuations of the well: for the water subsides in it when the stream issuing from the rock becomes languid; on the contrary the surface of the water rises again in the notch, so soon as the influx into the trough begins to be more copious. The reciprocations of the spring are easily observed by this contrivance; and they appear to be very irregular both in respect of duration and magnitude. For the interval of time betwixt any two succeeding flows, is sometimes greater, and at other times less, than a similar interval which the observer may happen to take for his standard of comparison. The rise of the water in the cistern, during the time of the well's flowing, is also equally uncertain; for it varies from one inch, to nine or ten inches, in the course of a few reciprocations. It is necessary to remark on the present occasion, that the spring discharges bubbles of air, more or less copiously into the trough; these appear in the greatest abundance at the commencement of a flow, and cease during the ebb, or at least issue from the rock very sparingly at that time. In fact, the appearance and disappearance of these bubbles, are circumstances equally inconstant with the rise and fall of the water. The irregularities exhibited by the ebbing and flowing well, during my short visit, diminished the respect which I formerly had for the popular theory, more especially when considered as a general explanation of reciprocating springs. This change of opinion was suggested by the caprices of the well; which were too many and too singular to be ascribed to the uniform operations of a single siphon, as we have seen already; and the accidental combination of several siphons in one fountain, is a conjecture too improbable in itself to demand a serious discussion. My suspicions respecting the accuracy of the principle were not a little increased, by the following descriptions of two reciprocating fountains. Weeding Well, in Derbyshire, appears to be more fickle and uncertain in its reciprocations, than the well at Giggleswick. Dr. Plot describes this remarkable fountain, at page 41 of his History of Staffordshire, where he reports it to be very uncertain in its motions, ebbing and flowing sometimes thrice in an hour, and at other times not oftener than once in a month; he also quotes the following character of it, to the same import, from a latin poem by Mr. Hobbs. "Fons hic temporibus nec tollitur (ut Mare) certis ; The following account of a reciprocating fountain is extracted from an article in the second volume of Lowthorp's Abridgement, page 305; in which care has been taken to preserve the facts recorded by the author, Dr. W. Oliver, in language more concise than his own. "Lay Well, near Terbay, is about six feet long, |