152 DR IN KING POOLS. 7. 



refervoir, to prevent the water, when the pond 

 is full, from running through it ; by which 

 means it becomes filted up unneceflarily. For 

 the nature of foul water is fuch, that when- 

 ever it changes from a current to a flagnant 

 flate, it depoiitcs a coniiderable part of its 

 foulncfs i io that the water which runs out 

 of a full refervoir is finer than that which 

 runs in •, the fediment of the furplus water 

 being left behind in the pond. Whereas, if 

 the current into the pond ceafe when the pond 

 is fufficiently filled, the fediment of the over- 

 plus water is got rid of. the pond receiving 

 in this cafe no other foulnefs than that which 

 is given by the quantity of water which is 

 required to fill it *. 



'The form of the refervoir is, univerfally, 

 that of a {hallow bafon, or more ftridly fpeak- 

 ing that of an inverted cone ; the fides llielv- 

 ino- llraight from the brim to an angle or 

 point m the center. If the excavation 

 be made fixty feet diameter, its greated: 



depth 



''■■ A fmall Catch Pool, between the run and the 

 refcrvo'.r, would arrcA much of the fouhicfs of water 

 coilcacdfrom a road ; and, in a fituation which would 

 :.dinit of it, would be worth the trouble of forming'. 



