548 I'HILOSOPHICAL TRANSACTIONS. [aNNO 1732. 



empty the cavern, then tlie fountain derived from r will, after some time, begin 

 to run again, and increase till the water rises in the cavern to n ; after which it 

 will decrease, and at length stop. But if the discharge of the syphon only 

 keeps the surface of the water below r, without emptying the cavern, then the 

 fountain derived from r shall be dried up, so long as the stream at o continues 

 increased; and shall run again when the said feeding-stream is lessened. Thus 

 we may have a spring which shall run all summer, and be dry all winter; such 

 a spring will increase just before it begins to fail, i.e. while the water in the 

 cavern is rising to n, will be dried up sooner in a wet summer, and break out 

 later in a wet winter, contrary to the nature of other springs. 



If the syphon mnp, fig. 12, of the reservoir abcd, having no outlet at r, 

 should discharge itself into a second reservoir efgh of a smaller capacity, but 

 furnished with a syphon stv, which discharges the water more plentifully than 

 it comes in; a fountain derived from this second syphon stv would flow and 

 intermit, while the first syphon mnp continued running; i. e. till the great reser- 

 voir ABCD should be emptied. After which it would entirely stop, till the said 

 reservoir abcd was filled again by the feeding-stream at o, and then it would 

 flow and intermit as before. 



Such a sort of compound fountain would be liable to all the variations of the 

 former fountains derived from a single reservoir, if we take the fits of flowing 

 and intermitting of this, for the flux of the former, and the long stop in this, 

 while the great reservoir is filling, for the pause or intermission of the former. 

 Besides, as the flux, in the former fountains may be changed, and be made 

 longer or shorter, so in this, the number of intermissions during one fit of 

 flowing and intermitting, may not always be the same, because of the different 

 capacities of the two reservoirs, and a difference or change occasioned in the 

 feeding-stream at o. For if, while the great reservoir abcd is emptying, the 

 little reservoir efgh should empty itself Q times, for instance, and be half full 

 again, the fountain derived from its syphon stv must have g intermissions in 

 one fit, and 10 in another, alternately, while the feeding-stream at o remains 

 the same. But the feeding-stream at o being lessened or enlarged, without 

 making the syphon mnp run continually, the number of intermissions in each 

 fit will be diminished or augmented accordingly. But it is peculiar to this last 

 sort of fountains, that in each fit of flowing and intermitting, the first flux 

 will be larger and longer than the second, and the second than the third; but 

 the first intermission will be shorter than the second, and the second than the 

 third; because the syphon mnp running faster at first than at last, the reservoir 

 FFGH must be a shorter time in being filled, and a longer time in being emptied, 

 the first time than the second, the second than the third, and so on. As to 



