of Mississippi and Louisiana 63 



mentary official collection of data from Port Eads, at the southern 

 end of the South Pass, indicates that the temperature variations 

 between these two places are slight. As the latter place may thus 

 be taken as a criterion of the conditions on the islands, we may 

 regard the New Orleans data as fairly close to the truth. 



It may, however, be mentioned in passing that our own obser- 

 vations during two weeks of August spent among the islands 

 proper showed a range of temperature between 26.6 C. and 30 C. 

 and a maximum daily range of only 3.4 C, the readings being 

 taken in the shade. It may also be mentioned in this connection 

 that the water temperatures showed about the same amount of va- 

 riation (27.i°-3o.5° C), and a mean temperature higher than that 

 of the air by o.s°-i° C. This continual high temperature of the 

 waters is due undoubtedly to their extreme shallowness over large 



areas. 



Precipitation 



as the 



The precipitation of this region is heavy and is composed al- 

 most entirely of rain. The records show a mean annual rainfall of 

 about 154.94 cm. (61 inches), less by 16.51 cm. (6}4 inches) than 

 than that of Ocracoke. This difference is of little or no physio- 

 logical importance because the vegetation is near the water table, 

 and because of the continuous high relative humidity. Only one 

 other region on the Atlantic Coast has as great a rainfall 

 Hatteras region and the one here considered, namely a part of 

 outhern Florida. The Delta region, however, is somewhat more 

 subject to sudden storms than Hatteras as is indicated by the rela- 

 tive frequency of thunder storms in the ratio of 4 to 3. Droughts 

 do not occur, as the rainfall is pretty evenly distributed through- 

 out the year, and there appears to be little or no tendency to con- 

 centrate it at any season of the year. Thus a given month which 

 s hows six or seven inches in one year may show as low an amount 

 as one or two in another year. 



Th 



Atmospheric Humidity 



e 



vary 



tween 66 and 84, the annual average being 77, less by 4.4 per 

 cent, than that of Ocracoke. The degree of humidity is however, 

 h'gh, and varies but little from month to month. 



