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 U, 1903, Bench Mark No. 3 was found 

 by spirit levels to be 14.1C8 feet above zero of the fixed tide staff, having been 

 set at exactly the same elevation as Bench Mark No. 2. 



Mean of 707 high waters on the fixed tide staff 4.332 ft. 



Meanof7071ow " '• " " " " -1.698 " 



Mean half-tide level " " " " " " 3.015 " 



Mean sea level " " " " " ■' 2.991 " 



Mean range of tide " " " " " " 2.634 " 



Elevation of Bench Marks. B. M. 1. B. M. 2. B. M. 3. 



ft. ft. ft. 



Above mean high water 6.176 9.776 9.776 



Above mean low water 8.810 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, we have 



HTL = ^{HW + L-W). 



Mean sea level is the mean of the hourly heights of the sea throughout the 

 year, or 



MSL = ~s iK + h, + h,+ h,, + h,,) 



in which :sh represents the sum of all the heights throughout the series for 

 the hour designated by the subscript. In a common year n = 34 X 365 and in 

 a leap year w = 34 X 366. 



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

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



HTL = MSL + M, cos {2MI — M^) — 0.04 ^-^i^'cos {Ml — K\— 01) 

 where 



HTL = mean half- tide level 



MSL = " sea level 

 Mi, Ml, Mi, Ml, Kx, K\, Oi, O", are harmonic constants defined further on. 



TIDES AT NASSAU. 



Tide Eecohds. 

 The tide record for Nassau 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 77° 21' or 5h. 09m. west of Greenwich. The heights are 

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

 so that they may be referred to the bench marks. 



