40 PHILOSOPHICAL TRANSACTIONS. [aNNO 17'24. 



all emptied; and as it discharges itself into anotlier tantalus tv, whose syphon 

 is at V, this last tantalus will also, when full, begin to run out, and its water 

 go down to XYO. 



If the plug be let down gradually, as soon as the water begins to run out of 

 the last tantalus tv, and the first tantalus rs be covered so as to be concealed 

 from sight, it will appear to the spectators, that the cavity tv, representing 

 a pond near an ebbing and flowing river (as it is said there is such an one at 

 Greenhithe in Kent, between London and Gravesend) always rises, while the 

 water at no, or the tide, falls to lm ; and always sinks while the water at lm, 

 or the tide, rises to on. 



Exper. 1. Let the water in the box abcd not be made use of; only the 

 vessel z be filled every half hour: it will empty itself in the space of a quarter 

 of an hour, falling like rain, and dropping also through the leaden platform ef 

 into the hidden tantalus rs, which will not begin to run till this artificial rain 

 is over: then in a quarter of an hour more, the tantalus rs will have emptied 

 itself into the visible tantalus tv, which will be filling all the time after z has 

 done running, or in the dry season, and as soon as tv is full, it will begin to 

 run out through its syphon v, at the end of the half hour, when the vessel z 

 or sieve runs again ; that is, at the return of the rainy season. 



This last experiment may easily be applied to those ponds, or those brooks, 

 that are high in dry weather, and low in wet weather ; of which kind it seems 

 there is a brook at Lambourn in Berkshire. 



If it be objected, that such ponds are full for some time, which a tantalus 

 cannot be, because it begins to run out as soon as full; that may be easily 

 solved, by supposing the hidden tantalus, or intermediate cavity between the 

 river and pond, to contain more water than the visible one, provided it does 

 not contain so much as not to be emptied, before the return of the tide. The 

 same solution will serve for wet and dry seasons, only supposing the cavities 

 larger. 



If it be asked, where the water of the visible tantalus, near a river, can 

 run; it maybe answered, that all this may happen, though the second, or 

 lowest tantalus, should have its bottom higher than low water-mark in the 

 river. And for the syphons, which are of a particular make in the cup; though 

 such be not supposed in the earth, yet any long passage, rising in the middle, 

 will answer the end. See fig. 5, where abcd represents the channel of a river, 

 AD high water-mark, and gh low water-mark ; zi a passage from the river to 

 the cavity iklmn, the first or hidden tantalus; lmq the syphon of the first 

 tantalus, running into the second tantalus, or visible pond oqrp, which by its 

 syphon rsv runs out into low grounds that may be above the low water-mark 



