NATURAL PHENOMENA OF THE EQUATORIAL REGIONS. 313 



mean temperature is 27° [80-6° F.] ; but the thermometer 



seldom rises to the extremes of heat, which it frequently 



attains in the north of Europe. In the equatorial regions Extremes of 



the extremes of the greatest and least heat are not more heatandcold ' 



than 16° or 20° [28*8° or 36 c ] distant; while in Europe 



they exceed 62° [81-6°]. 



From all the observations made by Mr. von H. on the The tempera- 

 Cordilleras it appears, that the decrease of temperature more rapTdl^a* 

 above 3500 met. [3825 yards] is more rapid in the propor- great heights. 

 tion of 5 to 3, than from the level of the sea to the height 

 of 2500 met. [2732 yards] : but it is to be remarked, that This influenced 

 the inequalities of the surface of the Earth have much tyf ty of the§ur« ~ 

 fluence on this decrement j and that a person going up to face, 

 the same heights in a balloon would find different results. 



Mr. yon Humboldt ascended Chimborazo to such a height, Heights ascead- 

 that the barometer fell to 0-37717 of a metre [ 14*84 inches] ; ^ 10r f lleaU " 

 its height at the level of the sea being settled at 076202 of 

 a met. [29-98 in.], and the temperature being 25° [77° F.]. 

 This differs a little from the estimation of Bouguer, who 

 made it 0*76022 of a met. [29-91 in.]. 



The elasticity of the air in the temperate zones varies ^ '^nations of 

 iA'j*/,. « r. ~- • t • *» i the barometer. 



sometimes 0-045 of a met. [177 in. J m the same place. 



Under the tropics, at the seaside, it varies only 0-0026 of 

 a met. [1-023 line]. In a separate table Mr. von H. gives 

 these variations at the different hours, at which they are 

 noticed. The progress of these variations under the equator, 

 at the level of the sea, supposing the mean term of the ba- 

 rometer = Z is as follows. 



At 21 hours = Z-f 0-5 At 11 hours = Z +0-1 



At 4 =Z~0-4 At 16 =Z-0-2 



These horary variations are not noticed in our climates, 

 on account of the many local causes, that occasion the ba- 

 rometer to rise or fall irregularly. 



Mr. von H. concludes his barometrical researches with Effect of the 

 some physiological observations on the connexion between ^'on respira- 

 respiration and the elasticity of the air. It appears thattion. 

 the inhabitants of the plains, accustomed to a pressure of 

 28 in. [29-84 Eng.], most easily support these variations 

 of the density of the air: they easily habituate themselves 

 ' -2 *> 



