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In a given liUitude, the rate of diminution at equal heights, Is 

 greater when the temperature below is high, than when it is low; 

 for while the divifor (viz. the height of the line of congelation) 

 remains unaltered in all temperatures, the dividend (viz. the 

 difference betwixt the heat below and 32^) is fj much the 

 greater as the temperature is higher, and confequently the 

 rate or qu'~'tient mull; be hij^her. Sauffure alfo noticed this 

 difi'erence of the rate of diminution in high and low tem- 

 peratures; for he tells us that in winter the rate of diminution 

 is but ^ of that which it amounts to in fummer. Voy. § 2051. 

 And between the tropics heat rifes much more rapidly than in 

 the higher latitudes, as Dr. Caffan obferved, 36 Roz. Jour. p. 265. 

 See alfo Mr. Six's obfervations in the Phil. Tranf. 1788, p. 105. 

 And hence the difference betwixt the temperature of mountains 

 and of plains is not fo great in winter as in fummer. Nay in 

 winter the temperature at great heights is often warmer than on 

 plains, as will prefently be fhewn. 



We owe to Mr. Pictet fome new and curious experiments on 

 the progrefs of heat at low heights; that is between 5 and 75 

 feet. He found that a thermometer, fufpended about five feet 

 over the earth, generally increafcd in heat more rapidly than a 

 thermometer placed 75 feet over the earth ; fo that on the hottell 

 hour of the day, the lower was often about 4,5 degrees warmer 

 than the upper thermometer. This fhews that the increafe of 

 heat below is quicker than its communication upwards. However 



towards 



