The Coastal Deserts of Jamaica. 133 



During the first week of July, 1909,aporous cup atmoneter 

 was exposed in the desert at a spot quite near the coast between 

 Cane and Hope rivers, and its reading co npared with that of 

 another cup at the Govern:iTient Laboratories in Hope Gardens, * 

 which are some six miles inland and behind a low ridge of hills. 

 Both cups were exposed to full sunshine. When reduced to the 

 amounts of loss per week from standard cups the readings are: 

 for the desert, 175 cc, for the Government Laboratory, 148 cc. 

 The location of the Laboratory subjected the cup there to several 

 short periods of cloudiness, probably six or eight hours in all, 

 while the entire week was clear at the desert cup; and operating 

 in the same direction was the occurrence of a much more con- 

 stant air movement at the coastal station. These factors amply 

 account for the small difference in the readings, a difference which 

 is quite incapable of serving to explain the difference between 

 the vegetation of the coastal desert and that of the Liguanea 

 Plain in the vicinity of the Laboratory. Some unpublished 

 figures obtained by Livingston and Shreve relative to the evapor- 

 ation rate in different parts of the United States show up the 

 much greater contrast between the rates for continental deserts 

 and for humid costal regions. The following are weekly rates, 

 averaged from the four weeks of July, and are reduced to the 

 same standard as those from Jamaica: 



Tucson, Arizona 358 cc. 



Miami, Florida 144 



Cameron, Louisiana 167 



San Diego, California 201 



The rate for the Government Laboratory is nearly that for 

 Miami, and the rate for the coastal desert is about half that for 

 the continental desert at Tucson, while it is near that for Cameron 

 which is situated on the Gulf coast and subjected to conditions 

 of temperature and air movement not unlike those on the Ja- 

 maican coast. The San Diego reading is of interest as coming 

 from a coastal region which partakes of the desert character in 

 its vegetation; and while somewhat higher than the reading for 

 the Jamaican desert it is still much lower than the Tucson read- 

 ing. 



While the leeward deserts of the West Indian islands are 



*I have to thank Mr. R. Simmons of the Government Laboratories for co-operation 

 in the taking of evaporation readings through several months. 



