156 RECORD AND RESULTS OF 



gation of the diurnal wave througli the Atlantic Ocean and up Baffin Bay. We 

 shall now enter more fully into the phenomena, and commence with the 



Diurnal Inequality in Height. — On Plate I the observed tides of the winter and 

 summer series have been laid dovsTi graphically in time and height ; this was done 

 directly from the numbers of Table II. The few wanting tides were interpolated, 

 and are shoAvn by dots. The high Avaters, depending on the moon's ii/pixr transit, 

 as well as the low waters following, which depend on the same transit, are dis- 

 tinguished from those high and low waters which follow the moon's loioer transit, 

 by a simple dot at their extremity ; whereas the latter have a small circle attached. 

 To render the diurnal inequality more conspicuous, the dots of the high and of the 

 low waters were each connected by a full line, and the circles by lines of dashes. 



The vertical distances between this full line and the line of dashes are re-plotted 

 on a straight axis (of abscissae) and exhibited below each series of observations, the 

 first for high, the second for low water. On the same axis zero declination (of the 

 moon) is indicated by a small circle, and greatest north or south declination by a 

 small bar. The diurnal inequality in height is greater for the high waters and less 

 for the low waters, and that liigli water which follows the moon's thp-per transit 

 (about 11 hours) when she has north declination is the higher of the two of that day;^ 

 when, on the contrary, she has sonth declination, it will be the lower of the two. 

 The same rule was found from the Rensselaer Harbor tides. For the low waters 

 the rule cannot conveniently be stated in this form owing to a remarkable circum- 

 stance, namely, the simultaneous occurrence of no inequality in the high waters with 

 greatest inequality in the low waters, and consequently also the occurrence of the 

 greatest high water inequality with no inequality in the low waters ; this is very 

 plainly shown in the diagrams on Plate I. This singular feature has heretofore, as 

 far as known to me, not been found for any station on the Atlantic, or depending 

 on this ocean for its tides ; but it was detected in Puget Sound on the Pacific, 

 which the reader wiU find noticed in the reports of the Superintendent of the U. S. 

 Coast Survey for the year 1859 (p. 144), and in three subsequent reports. The 

 rule, however, which applies there to the height of high water applies at Port 

 Foulke to the low water, and vice versa. 



The apparent retard of the high water epoch is as follows : — 



d'g declination zero. 



Inequality vanishes. 



Int 



erva 



18G0. Nov. 22", 0" A. M. 



23" (i^- P. M. 



1" 



12 



Dec. 5, 11 P. M. 



Y p. M. 



1 



19 



" 19, 7 A. M. 



21 (? P. M. 



2 



11 



1861. June 15, T A. M. 



10 4 P. M. 



1 



9 



" 28, 7 A. M. 



30 G P. M. 



2 



11 



On the average, therefore, the diurnal inequality in the height of high waters dis- 

 appears 1.9 day after the moon's passage over the equator; the corresponding 

 quantity at Van Rensselaer Harbor was 1.6 day. 



* This rule depends also on the particular transit of tho moon first fixed upon to connect with the 

 tide, and the desirability of extending the establishment.beyoud twelve hours ; thus the rule for high 

 water, given by the Rev. W. Whewell for our Atlantic coast (fith Series of Tidal Researches, Phil. 

 Trans. 1836) will be found the opposite of that given in our U, S. Coast Survey Reports for the 

 Pacific coast of the United States. Port Foulke follows the rule of the latter, 



