76 



RECORD AND REDUCTIOX OF THE TIDES. 



moon Ims north or south declination, positive and negative ordinatcs, in perfect 

 accordance with the equilibrium tlieory, according to which the tide (high water) 

 which belongs to a south transit of the moon should be the greater of the two of 

 the same day, the moon's declination being north, or should be the smaller of the 

 two, the moon having south declination ; when the moon crosses the equator (or, 

 according to experience, some time after it), the inequality vanishes ; the time by 

 which the full effect is produced is, as in other cases of the application of this 

 theory, later than theoretically indicated. On Plate III are given specimens of the 

 diurnal inequality curve, constructed as explained above and on the same scale as 

 the other diagrams on these plates. By means of the diagrams, the epoch when 

 the inequality vanishes has been made out as follows : — 



TABLE SnOWING THE OBSERVED TIMES WHEN THE DIURNAL INEQUALITY VANISHES, TOGETHER WITH THE 

 TIME WHEN THE MOON CROSSES THE EQUATOR, AND THE DIFFERENCE OF THESE TIMES, OR THE NUMBER 

 OF DAYS BY WHICH THE CAUSE PRECEDES THE EFFECT. THIS DIFFERENCE IS ALSO CALLED THE EPOCH. 



The results for the epoch are very regular, and with the exception of part of 

 the last series, which is of inferior accuracy, no observation has been omitted. 

 The inequality vanishes at the distance of 1.62 days' motion of the moon from her 

 nodes. 



The magnitude of the diurnal inequality, and its variation depending on twice 

 the moon's declination, was made out by dividing the inequality curves in six parts 

 between the times of disappearance, and by tabulating the ordinatcs as well as the 

 corresponding declination of the moon, the following results were obtained from 12 

 complete cycles, omitting no value, viz : — 



AMOUNT OF DIURNAL INEQUALITY IN THE HEIGHT OP HIGH WATER. 



