HYGIENE 



531 



TROPICAL HYGIENE, SANITATION, ETC. 



HYGIENE. 



CLIMATE. 



Castellaxi defines climate as " the combined effects of tlie sun, the 

 atmosphere, and the earth at any one place of the earth's surface." 



The sun exercises its influence by its heat, light and chemical ravs. 



The atmosphere by its chemical composition, temperature, dia- 

 thermacy, humidity, pressure, motion (winds) and electric conditions. 



The earth by its latitude, relative proportion of land and water, 

 ocean currents, soil vegetation, configuration of the surface and 

 altitude. 



TEMPERATURE. 



Climates known as tropical and subtropical lie between 35^^ X. and 

 35° S. (approximately) of the equator, the northern parallel being the 

 Tropic of Cancer and the southern being the Tropic of Capricorn. 



The sun is always vertical over some part of this broad belt, the 

 average mean temperature of which does not go below 68° F. (30° C). 



When the sun's rays are vertical, 80 per cent, of the sun's heat 

 that enters the atmosphere reaches the earth. As the sun's ravs become 

 more oblicjue less heat reaches the earth until probably none reaches 

 it, when the sun's rays are horizontal to it. 



The highest temperatures are reached over the two parallels men- 

 tioned above, because the sun remains vertical for the longest periods 

 over those parallels. 



The superficial land temperature may rise to 200° F. (93*3° C), 

 while superficial water temperature rarely exceeds 90° F. {^^'2'^ C). 



The mean temperature of the earth increases with its depth, about 

 1° C. per 28 metres. Thus mines in temperate zones may become 

 tropical or subtropical, and consequently tropical diseases, such as 

 ankvlostomiasis, may flourish there under suitable conditions, e.g-., 

 the tin mines of Cornwall. 



A daily range of temperature of more than about 20° F. (11° C.) 

 is apt to be dangerous if precautions are not taken. Short journeys 



