340 Tuttle — Changes in Elevation of Land and Sea. 



Half tide level above Battery datum. 





Pier A. 



West 57th St. 



East 24th St 



1889 



2-273 ft. 



2-079 ft. 







1890 



2-063 



1-990 



.. - - - 



1891 



2-012 



2-082 



- -. - . 



1892 



1-910 



1-902 



- _ - - 



1893 



2-232 



2-075 







1894 



2-133 



2-075 



2-164 ft 



1895 



2-265 



2-018 



2-067 



1896 



2-314 



2-003 



2-053 



1897 



2-359 



2-212 



2-173 



1898 



2-258 



2-278 



2*301 



1899 



• 2-230 



2-245 



2-127 



1900 



2-250 



2-127 



2-012 



1901 



2-514 



2-461 



2-274 



1902 



2-490 



2-492 



2-361 



1903 



2-343 



2-433 



2-295 



The yearly averages of half tide level at New York which 

 have been given, are plotted in the diagram on page 339. 

 They show a continual oscillation, having an amplitude of 

 nearly 0*3 ft., about an average value which since 1875 has 

 uniformly increased. These oscillations when considered in 

 relation to the accompanying meteorological phenomena, also 

 represented in the diagram, are seen to be mainly due to atmos- 

 pheric pressure and winds. They are more or less perfectly 

 eliminated by taking the average for five or more years, and 

 when thus eliminated the observations appear to show that mean 

 sea level remained nearly stationary from 1853 to 1875, since 

 which time it has been rising relatively to the land by about 

 1'45 ft. per century. The rate of change since 1875 may be 

 obtained in the following different ways. 



(1) From ten years' observations at Governor's Island, 1870- 

 79, the elevation of M. S. L. was 1*932 ft., and at Fort Hamil- 

 ton the average elevation of H. T. L. from 1893-1902 was 

 2-165 ft. ; allowing 0'03 ft. as the difference between M. S. L. 

 and H. T. L. at Fort Hamilton, we have an increase in eleva- 

 tion of H. T. L. of 0*26 ft. in twenty-three years, or 1*1 ft. 

 per century. 



(2) The observations at Fort Hamilton alone, give the follow- 

 ing result by taking the average H. T. L. of the first five and 

 last five years of the series : 



H. T. L. 1893-97 elevation 2-108 ft. 



H. T. L. 1898-1902 " 2*223 



An average elevation of H. T. L. of *115 ft. in five years, or 

 2*30 ft. per century. 



(3) The tidal observations at Pier A for the last ten years. 



