ii6 An ESSAY Chap. 3. 



When they are drawn up a conGderablc 

 height, the Strength of the Air that is under, 

 and which is ftill greater and greater, and 

 undulating by its Motion this way, that way, 

 and the other, ( they rife gradually through 

 the Air 5 ) and this is very plainly demonftra- 

 ble, from the Paper-Kites that School-Boys 

 ufe in their Diverfions, which being elevated 

 fixteen or eighteen Yards, rife eafier, and with 

 greater celerity 5 and the longer their Line 

 is, ftill the better 5 fince the higher they ad- 

 vance, the ftronger and better they jfliy. But 

 to thefe Vapours : 



When they arrive into the higher Regions 

 of the Air, the Frigidity thereof foon aggre- 

 gates and condenfes them into Bodies and 

 Clouds, which are blown here and there, 

 but are ftill fufpended, ""till the genial Difpo- 

 fition of the Sun, or the natural Warmth, 

 Humidity, and Rarefadion of the Air re- 

 leafes them from their Imprifonment. 



There is a Difpute between the Philofo- 

 phers, whether Nubis or Nebula be of the 

 fame Difpofition > By the firft, I under- 

 ftand that general Cloud of Darknefs that 

 very often intercepts the Sun from our 

 View 5 and by the other, thofe fmaller fly- 

 ing Clouds that are difcoverable in a Sun- 

 iliiny Day. 



Some of them affirm, that That general 

 Cloud we underftand by the Word h'ubis, is 

 of a heavier, thicker, and clofer Difpofition, 

 not unlike a large Body compos'd of Flakes 



of 



