6 TROPICAL NATURE, AND OTHER ESSAYS. 



Causes of the Uniform High Temperature near the 

 Equator. It is popularly supposed that the uniform 

 high temperature of the tropics is sufficiently explained 

 by the greater altitude, and therefore greater heating- 

 power, of the midday sun ; but a little consideration will 

 show that this alone by no means accounts for the 

 phenomenon. The island of Java is situated in from 

 six and a half to eight and a half degrees of south 

 latitude, and in the month of June the sun's altitude 

 at noon will not be more than from 58 to 60. In the 

 same month at London, which is fifty-two and a half 

 degrees of north latitude, the sun's noonday altitude is 62. 

 But besides this difference of altitude in favour of London 

 there is a still more important difference ; for in Java the 

 day is only about eleven and a half hours long in the month 

 of June, while at London it is sixteen hours long, so that 

 the total amount of sun-heat received by the earth must 

 be then very much greater at London than at Batavia. 

 Yet at the former place the mean temperature of the 

 day and night is under 60 Fahr., while in the latter place 

 it is 80 Fahr., the daily maximum being on the average 

 in the one case about 68 and in the other about 89. 



Neither does the temperature at the same place depend 

 upon the height of the sun at noon ; for at Batavia it 

 is nearly vertical during October and February, but 

 these are far from being the hottest months, which are 

 May, June, and September ; while December, January, 

 and February are the coldest months, although then the 

 sun attains nearly its greatest altitude. It is evident, 

 therefore, that a difference of 30 in the altitude of the 

 sun at noon has no apparent influence in raising the 

 temperature of a place near the equator, and we must 



