114 Papers from the Department of Marine Biology. 



lived in the Tortugas, when for periods of several weeks there was a 

 continuous succession of clear, brilliantly sunny dayf. with not even an 

 occasional tropical storm or squall. According to Ihe meteorological 

 summary for Miami, the total average of clear da/s is only 68 and 

 partly cloudy 135. The comparison again, with the record for Key 

 West, with its average of 151 days, taken together with the difference 

 in total precipitation, shows the cUmate of the southernmost keys to be 

 sUghtly drier than that of the mainland. This difference is perhaps due 

 largely to the prevailing winds. 



The prevailing winds are eastwardly, as reported by the Weather 

 Bureau at Key West, and as also observed at Tortugas by Vaughan, in 

 liis paper on the influence of the prevaihng wind in atoll formation, 

 and also by the writer in various physiological experiments undertaken 

 at the latter place. The velocity of these winds is very variable. The 

 average velocity is 9.6 miles per hour. But in this region of hurricanes 

 all winds over 75 miles per hour are rated as hurricane winds. These 

 usually occur in the fall during the months in which the heaviest 

 precipitation occurs, viz, September, October, and November, which 

 months are called the "hurricane months." In the Gulf region, as 

 recorded b}^ the Key West office, the following severe hurricanes, of 

 which the directions and velocities are here given, did a great deal 

 of damage: On September 25, 1894, 87 miles per hour from the south- 

 west; October 19, 1896, 88 miles per hour from the southwest; October 

 n, 1909, 83 miles from the northeast; October 17, 1910, 100 miles per 

 hour from the south. This last hurricane, known as the ''great hurri- 

 cane of 1910," not only did vast damage on land but, as observed by 

 the writer and others by means of a diving helmet and glass-bottomed 

 boats, the coral and sponge fauna and the algal flora of the sea-bottom 

 in the region suffered great changes and in some places on the bottom 

 immense windrows of broken corals may still be seen which were 

 mashed and heaped up by the force of giant wind-driven waves. 



The temperature of the Tortugas is fairly constant. The variations 

 in January and February, which are the coolest months, range from 60° 

 F. as a minimum for these months to 75° F. as the maximum; in June, 

 July, and August, which are perhaps the hottest months, the minimum 

 is 77° F. and the maximum 88° F. The Key West records show the 

 average annual temperature to be 76.8° F. and for the entire period 

 over which the records extend — i. e., 1871 to 1913 inclusive — the maxi- 

 mum was 100° F. and the minimum 41° F. For Miami the mean 

 annual maximum temperature is 80° F. and the minimum is 68° F. ; 

 that is, the annual mean temperature is shghtly lower than that of the 

 Tortugas and the southern keys. 



