24 U. S. COAST AND GEODETIC SURVEY 



Boston and East Boston. The total lengths of series used for the 

 analyses at these stations were 5, 14, and 6 days, respectively. For 

 station W16 two separate analyses were made, one for a 10-day 

 series and the other for a 4-day series. 



Because of the shortness of these series, the usual elimination 

 processes were not applicable, but corrections were made by com- 

 parison with tidal harmonic constants derived from simultaneous tide 

 observations at Commonwealth Pier No. 5, Boston. The analyses 

 were made for components M2, M4, Me, N2, S2, Ki, and d, and values 

 for other components were inferred from these principal components 

 and from the tidal components for Boston. The harmonic constants 

 are given in Table 35. 



The consistency of the results derived from the several series indi- 

 cates that the semidiurnal components for these stations have been 

 reasonably well determined, notwithstanding the shortness of the 

 series of observations upon which they are based. The constants 

 derived for the diurnal components, especially the epochs for these 

 components, are less well determined. Because of the small ampli- 

 tude of these components and also of components M4, and Mg, the 

 epochs are very sensitive to any small irregularities introduced by 

 accidental conditions. On the other hand, the small amplitudes of 

 these components in this locality render them of little practical 

 importance. 



Station W16, off Deer Island Light at the entrance to President 

 Roads, is a principal current station for which predictions are given 

 in the current tables published annually by this bureau. Hereafter 

 these predictions wil. be based upon the harmonic constants in 

 Table 35. 



CURRENT OBSERVATIONS, BOSTON LIGHT VESSEL 



There have been two series of current observations at the Boston 

 Light Vessel in accordance with a general plan for obtaining such 

 observations through a cooperative arrangement between the Coast 

 and Geodetic Survey and the Bureau of Lighthouses. The first 

 series of current observations at the Boston Light Vessel covers the 

 period September 22 to December 26, 1913, and the second series 

 June 8, 1926, to June 30, 1927. The apparatus consisted of a log 

 line graduated for a run of 60 seconds, a 15-foot current pole weighted 

 to float with 1 foot of its length above water, a pelorus, and a stop 

 watch or sand glass, the latter having been used for the earlier obser- 

 vations. An. observation was taken each hour of the day. 



The tidal current in this locality is weak and slightly rotary and 

 is affected to a considerable extent by the wind. In general the 

 velocities are less than one-half knot. The maximum velocity 

 recorded was 1 knot, which occurred on April 7, 1927, during a north- 

 west gale and at a time when the normal tidal current would have 

 been easterly. The wind therefore tended to increase the normal 

 velocity and also to divert the direction of the current to the south 

 of east. 



Tidal current. — In reducing these records the observed velocities 

 were resolved in north and east directions and then referred to the 

 times of high water at Boston, the earlier series being referred to the 

 predicted tides for the navy yard and the later series to the observed 



