CHAPTER III 



METEOROLOGICAL AND TOPOGRAPHICAL CONDITIONS. 



TOPOGRAPHICAL CHANGES AND THEIR BEARING 



ON ISTHMIAN ANOPHELES 



HTHE Isthmian Canal Zone has a tropical climate, 

 high humidity, heavy rainfall, and a short 

 dry season of four months or less. The continental 

 divide occurs at Culebra about twelve miles from 

 the Pacific canal terminal. North of Culebra all 

 drainage goes to the Atlantic Ocean through the 

 Chagres Valley. The attached Table No. i de- 

 scribing the air temperature fori9i2 shows the sea- 

 sonal variation to be very slight, with no excessive 

 heat, and no marked difference of temperature at 

 different points in the Zone. It always remains 

 within limits that are favorable to the development 

 of mosquito life. 



The yearly rainfall is not equal in all parts of 

 the Canal Zone. The extremes are noted at Colon 

 and Panama. On lands adjacent to the Pacific 

 coast, near the city of Panama, the precipitation 



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