i 6 Hydraulics.

Water in Wells also is owing to the Weightof that in the subterranean Cisterns from

whence

18. The several Sorts of Springs observed are (i.)Common Springs, which either run continually, and thenthey are called Perennial Springs ; or else run only fora l ime, or at certain Times of the Year, and thenthey are called Temporary Springs . (2.) Intermitting

Springs, or such as flow and then stop, and flow andstop again, by regular Alternations or Intermissions.(3.) Reciprocating Springs, whose Waters rife and fall,or flow and ebb, by regular Intervals, or Reciprocationsof .the Surface. All which are produced after the follow-ing Manner.

Plate 19. Let AB C D E represent the Declivity of a Hill,

XVII. whose Section, from Top to Bottom perpendicularly,Fig. 1. is shewn in the Figure ; in which let F G H be a Ca-vern or Bason near the Top which collects the Watergleeting through the Crannies, and has a Drain or Ductleading from H to the Side of the Hill at B. ’Tisevident when the Water rises to the Drain H, it willdescend through it to B, where it will break out inForm of a Fountain or Spring, and will continue thus,so long as the Reservoir is supplied with Water above »the Level F H, and after that it will become dry. Thuswe fee a Spring may be generated, near the Top of thehighest Hills or Mountains. Of this we have a not-able Instance near the Top of Landfdown Hill byBath. 1

20. There is one odd Pheenomenon of such Springsthat is sometimes observed, and that is, that they rutlin dry Weather, and are dry in wet Weather ; to accountfor which, we need only observe, that while the Wea-ther continues wet, the Waters are gathering into theBason or Reservoir, till there is a sufficient Quantityto run over and make the Spring play, by that Timethe Weather is altered and become dry; during the dryWeather, the Remains of the last Rains (for theseSprings proceed chiefly from Rain-Water) are conti-nually feeding the Reservoir, and by that Means sup-plying the Spring, but by the Time these are all spent,

the