I 407 ] 



Section VI. 



■Of the y arid Jons of the Temperature of the Summer and Winter 

 Seafons that take place in different Tears. 



To reafon with precifion on this fubjedi, we mnfi; at firft ab- 

 ftiad from all fublunary phyfical'caufes, and indicate the tempe- 

 rature appropriated to different latitudes from mere agronomical 

 confiderations. 



Halley has ingenioufly refolved this problem fo far as the mere 

 ratios of heat in the different feafons are concerned. 2 Phil. Tranf. 

 Abr, p. 165. And Lambert in his Pyrometric, § 596. 



Halley, calculating the ratios of heat communicated by the fun 

 to the earth, (which he confiders merely as a planet, abftrading 

 from all diftindion of land and water) in the different feafons in 

 the northern hemifphere, reduces thefe feafons to three, the equi- 

 noxes, the fummer folfiice, and the winter folftice ; and attending 

 only to the fines of incidence of the fun's rays, and the duration of 

 their adion, he fcts the heat communicated at latitude o. On the 

 days of the vernal and autumnal equinoxes at 20000. And on the 

 tropical days in the fame latitude at 18341. And then adds the 

 ratios which the heat in every lolh degree of north latitude bears 

 to thefe at the fame periods. Lambert adds the ratios of lat. 49^^ 

 and 66°, 33', flating the equatorial heat on. the equinoxial day at 999. 



3 E 2 But 



