546 I'HILOSOFHICAL TRANSACTIONS. [aNNO 1732. 



of which passing through two cavtrns or natural reservoirs with syphons, meets 

 with the other stream in a third reservoir, without a syphon ; where being 

 joined, they come out of the earth together. 



The petitio principii, or supposition of reservoirs and syphons in the bowels 

 of the earth, has been made by others : Pcre Regnauh, in his Phil. Conver- 

 sations, Vol. ii. Conv. 6, p. 125, &c. Eng. edit, has mentioned it in general; 

 and Dr. Desaguliers, in Phil. Trans. N" 384, has attempted to apply it to two 

 cases in particular; as Dechales, Tract, xvii. de Fonlibus Naturalibus, &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 syphon. 



A natural reservoir then, abcd, lig. 10, pi. 14, with such a natural syphon, 

 MNP, may be supposed. Let a feeding stream enter it, near the top at o. The 

 cavern must contain all the water which comes in at o, till it is filled to the 

 top of the syphon at n. Then the syphon beginning to play, and being sup- 

 posed always to discharge more water than comes in by the feeding-stream at o, 

 will empty the cavern, till the water is sunk in it below the mouth of the 

 syphon at m ; when it must stop, till the cavern is filled, and the syphon runs 

 again as before. If the water discharged by such a syphon, mp, be brought 

 out of the earth by a channel pq, the water will flow out of the earth, and stop 

 alternately, making an intermitting fountain at «. 



By this plain and easy contrivance, several of the flowing and ebbing springs, 

 observed by the naturalists, may probably be explained ; and even a much 

 greater variety of them than is hitherto known. For if the feeding-stream at o 

 should arise only from the rains in winter, or from the melting of the snow in 

 summer, the intermitting fountain would become a temporary spring, as Dr. 

 Plot calls such springs which are confined lo a season. Or if the feeding- 

 stream at o should be constant, but yet liable with other springs to an increase 

 and decrease, arising from the seasons, weather, or other causes, the con- 

 struction of the syphon would make a great alteration. For when the syphon 



