142 RECORD AND RESULTS OF 



21st and 28th, +2.1 feet; and between June 29th and July 5th, +1.2 foot. The 

 mean level reading for Series I is 16.7, and for Series II 17.9 feet; these levels, 

 however, are disconnected. 



General Character of the Port FouJke Tides. — We find by the subsequent. analysis 

 of the two series of observations, with respect to the half-monthly and the diurnal 

 inequalities, that their general character is very much the same as that exhibited 

 by the Van Rensselaer Harbor tides, a result which was to be expected since the 

 two localities are but 55 statute miles apart (following the sinuosities of the coast 

 line), with no apparent special configuration of the shore which might exert an 

 influence on the tidal feature. The establishment at Port Foulke is nearly half an 

 hour less than that of Van Rensselaer Harbor, consistent with the nortlierly (and 

 easterly) propagation of the tidal wave. The average range of the tide is almost 

 exactly the same at the two places. There is at Port Foulke a considerable diurnal 

 inequality which almost reaches, at certain times, that limit beyond which a single- 

 day tide is produced ; the diurnal inequality in the height of high water is greater 

 than in the height of low wafer ; these features of the diurnal inequality are also 

 common to the two localities. 



AVe shall now proceed with the special investigation of the inequalities commenc- 

 ing with that which runs through its period in half a month. For this purpose 

 Table II has been prepared. The second column contains the time of the moon's 

 transit over the Port Foulke meridian, interpolated from the American Nautical 

 Almanac ; the lower transit is distinguished by being placed between brackets. 

 The epochs of high and low tides are taken from Table I. Mean time has been 

 adopted throughout, as no special advantage can be derived from the use of apparent 

 time for so short a series of observations. The transit of the moon given is that one 

 which immediately precedes the time of high or low water ; the lunitidal intervals 

 are given accordingly ; those within brackets depend upon the lower transit of the 

 moon. The fact that various anterior positions of the moon are required for the 

 explanation of various tidal inequalities justifies us in using, in a first investigation, 

 the preceding transit; the subject will again be referred to in connection with the 

 moon's parallactic and declination effects. The reason why no one anterior lunar 

 epoch will answer, even for ports on the same coast and at no very great distance 

 apart, must be sought for, I think, in the compound character of the wave, com- 

 posed of propagated and direct effects, the velocity of the various parts being 

 differently affected by the variations in the depth of the sea over which these 

 waves pass. 



