62 U. S. COAST AND GEODETIC SURVEY 



Table 23. — Mean sea level referred to sea-level datum, Commonwealth Pier No. b 



Above table is derived by referring the values in Table 22 to the sea-level datum defined on p. 41. 



Table 24. — Difference between mean sea level and mean tide level, Commonwealth 



Pier No. 5 



The above table was prepared by subtracting the mean tide level as computed from the high and 1 ow 

 waters for each month from the mean sea level as computed from the hourly heights for the corresponding 

 month. 



Table 25. — Summary of time relations, Boston Navy Yard and Commonwealth 



Pier No. o 



Times are given in hours and decimals. Intervals marked "a" refer exclusively to the moon's upper 

 meridian passage at its north declination and to the lower meridian passage at "the south declination. 

 Intervals marked "b" refer exclusively to the moon's lower meridian passage at its north declination and 

 to the upper meridian passage at the south declination. 



For explanation of time relations, see pp. 10, 17. 



