the South-Sed. 



tains, &s AC maybe, muft be lighted three Quarters' of 

 the Day • but we know, that from Sun-riling till Nine of 

 the Clock, the Obliquity of his Rays on the general Face^ 

 and the Opposition of an Air condens'd by the Cold of fif- 

 teen Hours Abfence,, on which they muft have an Effedk to 

 put it into Motion, render his A&ion but little fenfible till 

 he is got up to a certain Height; for according to fome 

 able Philofophers, Cold confifts in aceafing from Motior\ 

 3. If one Mountain is contiguous to another, it is evi- 

 dent that the fame will be cover' d till the Sun has attained 

 the Height of the Angle TDC, which the Horizon forms 

 with the Line drawn from the Foot of one Mountain to the 

 Top of the other 5 then the Sun will not operate on all the 

 FaceE D above fix Honrs j and tho' he operates a long time 

 on the Top, it will be.never the more heated, becaufe the 

 Rays reflect upwards, as S A to N, where their Operation 

 is interrupted by the continual Flux of the Air, whofe vi- 

 olent Agitation in a ftrait Line is oppofite to the Heat, as 

 Experience fhews by the Wind, or if you pleafe by a ftrong 

 Blaft, clofing tlie Lips, which cools the Hand that receives 

 it. 



In fine, when the Sun, being in the Zenith, violently 

 heats the Plain, it only half heats the Mountains, as is plain 

 to thofe who undeiftand a little of Geometry ; for fuppo- 

 fing the Rays of the Sun Parallel, the Surface E D receives 

 ' no more than the Perpendicular E Y, equal to X D, which 

 may be look'dupon as in the Plain, tno the Line EYbe 

 much longer, but the Triangle being rectangular, and Ifo- 

 fceles^ the Squares of thofe Lin'es which exprels like Surfaces, 

 being to one another as 25 ^049, that is, almoft as 1 is to 

 2, it will appear, that the Mountain receives half the Rays 

 lefs than the Plain, which anfwers to a Quarter of the na- 

 tural Day, as in the firft.Cafe ; the Sun there will require 

 half as much more Time to render the Earch doable of 

 producing on the Mountain, than it will need on the Plain ; 

 therefore theHarveft will be long after, and it is not to*be 

 wonder'd that this Difference Ihould extend to fix Months. 



H h 2 I Ml 



