i CLIMATE AND ASPECTS OF THE EQUATORIAL ZONE 221 



places, 90 Fahr. being sometimes reached with us and not 

 being often very much exceeded at Batavia. 



Causes of the uniform High Temperature near the Eguatw 

 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 -one 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 Sep- 

 tember, 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, at different times of 

 the year, has no apparent influence in raising the temperature 

 of a place near the equator, and hence we conclude that other 

 agencies are at work which often completely neutralise the 

 effect which increased altitude must undoubtedly exert. 



There is another important difference between the tem- 

 perate and tropical zones, in the direct heating effect of the 

 sun's rays independently of altitude. In England the noon- 

 day sun in the month of June rarely inconveniences us or 



