338 Tuttle — Changes in Elevation of Land and Sea. 



Governor's Island, above B. M. T. Sandy Hook was 1*361 ft., 

 while from the simultaneous tidal observations of October, 

 1886, the difference was 1*468 ft., and from the tidal observations 

 of 1876-9, 1*472 ft. This latter difference has been adopted in 

 the reduction. 



The observations at Sandy Hook have to be reduced to the 

 equivalent values of half tide level at Governor's Island, which 

 for the ten years 1870-79 was *067 ft. lower than mean sea level, 

 and consequently the elevations have been corrected by this 

 amount in the column " Equivalent H. T. L. at Governor's 

 Island above Battery datum." 



The tidal records at Governor's Island from 1870-79 are par- 

 ticularly important in this investigation, and while the observa- 

 tions appear to be satisfactory, the frequent change of staffs 

 make it desirable to have an independent check on their accu- 

 racy which we have in the observations at Sandy Hook in 

 1876-79, taken in connection with the levels obtained from the 

 simultaneous tidal observations in October, 1886. 



We next have a series of tidal observations at Fort Hamilton, 

 K Y., from 1893-1902, as follows : 





H. T. L. above 



H. 



T. L. above 



Year. 



zero of staff. 



Battery datum. 



1893 



5-815 ft. 





2*067 ft. 



1894 



5-885 





2*137 



1895 



5*785 





2*037 



1896 



5*875 





2*127 



1897 



5*945 





2*197 



1898 



5*960 





2*212 



1899 



5*955 





2*207 



1900 



5-820 





2*072 



1901 



6*030 





2-282 



1902 



6*085 





2337 



The zero of the gauge at Fort Hamilton was 42*194 ft. below 

 B. M. L. (destroyed in 1901), and 17*951 ft. below B. M., 

 at Governor's Island, according to the Coast and Geodetic 

 Survey levels of 1887. Two independent determinations of 

 this difference in elevation have since been made, one in 1898 

 of 17*971 ft., and in 1900 of 18*019 ft. The 1887 value has 

 been adopted, however, in the reduction of the staff read- 

 ings to Battery datum. 



Besides the above observations of the Coast and Geodetic 

 Survey, we have the following tidal records of the Department 

 of Docks and Ferries, all referred to Battery datum. 



