34 INTRODUCTION', 



iifually as high as 78." I do not find that Mr. Marf- 

 den has mentioned the degree of heat of the fprings 

 in Sumatra. 



Dr. Mofely, in his book on Tropical Difeafes, fays, 

 ^' In countries between the tropics the heat is nearly 

 uniform, and feldoni has been known to vary through 

 the year on any given fpot, either by day or night, 

 more than 16 degrees. It is at a medium on the 

 coafl, and on the plains not much elevated above the 

 ]evel of the fea, at about Bo degrees of Fahrenheit's, 

 or ai 21 degrees of Reaumer's thermometer." 



From what I have already mentioned it appears, 

 that the heat of the wells of Kingflon in Jamaica is 

 about 30 degrees hotter than the wells in the neigh- 

 bourhood of London, and the difference of the heat 

 of the air is nearly the fame* Kingfton in Jamaica, 

 where the mean heat of the wells and air is So, is 

 about 17° north of the equator, and London about 

 51°; the difference, therefore, between London and 

 Kingflon is 34°, fo that the heat of the wells and air, 

 on a medium, increafes from London to Kingflon 

 about one degree of heat to every degree of latitude *. 

 Hence might we not, with fome degree of probabi- 

 lity, infer, that as the increafe of heat in 34° o-f lati- 

 tude is 30, the heat in 17° of latitude may increafe at 

 leall I o" ; and if it did, it would make the mean heat at 

 the equator 90 degrees. And, for my own part, 1 am 

 flrongly inclined to think, that at the centre of the 

 globe the mean heat of the air, as well as of the 

 earth, is about 90 degrees of Fahrenheit's thermo- 



* Andfo it does between Edinburgli and London. 



meter* 



