BOOK III. CHAP. VII. 6ss' 



Lat. N. Sun in S 



o 18.341 



10 20.290 



20 21.737 



30 22.651 



40 23.048 



50 22.991 



60 22.773 



70 23.543 



80 24.673 



90 25-055 



From this table we find the heat of the Northern part of Green- 

 land, which lies in lat. 80, compared with the heat on the Northern 

 part of Hifpaniola, which lies in lat. 20, is as 24.673, to 21.737, ^^ 

 lome days when the fun is moving through this quarter of the 

 Ecliptic; for it is the length of time that the heat is applied to any 

 particular country, as well as the degree of it, that determines the 

 quantity of heat communicated to it. Where, therefore, the days 

 and nights are of pretty equal length, the fun's heat cannot exert 

 itfelf lb powerfully, as where there is no night, and confequently no 

 interruption to its aftion for many months ; and the heat, which 

 arifes limply from the prefence of the fun, is, from Halley's theory, 

 reducible to this problem, viz. that the lun's heat, for any Imall 

 portion of time, is as a redangle, contained under the fine of the 

 angle of incidence of the rays producing heat at that time. 



For thele complicated reafons, although, when the funis vertical, 

 and darts a perpendicular ray, it is fuppofed to ihike with gieateft 

 force; yet, in thole countries where it is vertical twice a year, in 

 palling to and from the Tropic of Cancer, the greateft heat is not 

 during the inlfant of its verticalities, but fome weeks after, when it 

 is returning from one Tropic to the other, and its ray^ oblique. 



A Dutch captain afferted, that he had been quite under the North 

 Pole, where he found the climate as temperate as at Amftercam, and 

 the lea quite open. This aflertion has been deemed not imj robable, 

 confidering that the fun's rays, though falling very obliquely in that 

 latitude, mull neverthelels produce a very great degree of heat, from 

 his long continuance above the horizon ; lo, notwithftanding the 

 obliquity of the rays, it is found, that in the middle of iummer the 

 thermometer fometimes rifes higher in Sweden, and at Pcteriburgh, 

 than under the Line. 



But, for the better comparifon of climates, and the degrees of heat, 

 under different or under parjlicl latitudes,, it is greatly to be wilhed, 



that. 



