MOISTURE OF THE ATMOSPHEHE. 



9 



night to keep up a liigh temperature in the absence of the 

 sun. At the equator, on the other hand, this radiation 

 is always going on, and earth-heat is one of the most 

 important of the agencies which tend to equalise the 

 equatorial climate. 



Influence of the Aqueous Vapour of the Atmosphere. 

 — The aqueous vapour which is always present in 

 considerable quantities in the atmosphere, exhibits 

 a singular and very important relation to solar and 

 terrestrial heat. The rays of the sun pass through it 

 unobstructed to the earth ; but the warmth given off by 

 the heated earth is very largely absorbed by it, thus 

 raising the temperature of the air ; and as it is the 

 lower strata of air which contain most vapour these act 

 as a blanket to the earth, preventing it from losing heat 

 at night by radiation into space. During a large part 

 of the year the air in the equatorial zone is nearly 

 saturated with vapour, so that, notwithstanding the heat, 

 salt and sugar become liquid, and all articles of iron get 

 thickly coated with rust. Complete saturation being 

 represented by 100, the daily average of greatest 

 humidity at Batavia reaches 96 in January and 92 in 

 December. In January, which is the dampest month, 

 the range of humidity is small (77 to 96), and at this 

 time the range of temperature is also least ; while in 

 September, with a greater daily range of humidity (62 

 to 92) the range of temperature is the greatest, and the 

 lowest temperatures are recorded in this and the pre- 

 ceding month. It is a curious fact, that in many parts 

 of England the degree of humidity as measured by the 

 comparative saturation of the air, is as great as that of 

 Batavia or even greater. A register kept at Clifton 



