THE BAHAMA ISLANDS 53 



about 3 inches in diameter, which is cemented into the west stone wall of the 

 Clifton Hotel, about 5 feet above the ground. This building is also very old 

 and therefore quite stable. On June 26, 1903, Bench Mark N"o. 3 was found 

 by spirit levels to be ]4.1( 8 feet above zero of the fixed tide staff, having been 

 set at exactly the same elevation as Bench Mark Xo. 2. 



Mean of 707 high waters on the fixed tide staff 4.33'2 ft. 



Mean of 707 low " '• ' 1.698 '■ 



Mean half-tide level " " " " " " 3.015 •' 



Mean sea level " " " " " " 2.991 " 



Mean range of tide " " " " " *' '2.63-1 " 



Elevation of liencb Marks. IJ. M. 1. 15. M. 2. B. M. 3. 



ft. ft. ft. 



Above mean high water 6.176 9.776 9.776 



Above mean low water s.810 12.410 12.410 



Above mean half-tide level 7.493 11.093 11.093 



Above mean sea level 7.517 11.117 11.117 



Mean half-tide level is the mean of all the high and low waters for the 



year, that is, if we abbreviate to initial letters, Ave have 



]\rean sea level is the mean of the hourly heights of the sea throughout tlie 

 year, or 



MSL = ---'■ (//„ + /^ -4- //„ + h,, -f It.,,) 



in which 2'// represents the sum of all the heights throughout the series for 

 the hour designated by the subscript. In a common year n = 24 X 365 and in 

 a leap year » = 24 X 366. 



When the harmonic constants for the station are known, the approximate 

 \alue of mean half-tide level may be computed by the formula 



HTL z= MSL + M, cos (2J/S — M\) — 0.04 *^^-±=^'cos {Ml — K\ — 01) 



Avhere 



HTL = mean half-tide level 

 MSL = " sea level 



i/o, M\, 3L, M'l /r,, A'i', 0,, 0? are liarmonic constants defined further on. 



TIDES AT NASSAU. 



Tide Eecords. 

 The tide record for Xassau consists of curves traced by the tide gauge, 

 and these marigrams or tide curves were tabulated in order to obtain the hourly 

 heights of the sea. and the times and heights of high and low waters which are 

 given here. The time used is mean local civil for Nassau, the approximate 

 time meridian being TT° 21' or 5h. 09m. west of (rreenwich. The heights are 

 expressed in English feet and tenths, and are reduced to the fixed tide stafi", 

 so that thev mav be referred to the bench marks. 



