RECORD AND REDUCTION OF THE TIDES. 



feet (on account of the diurnal inequality), the mean level only oscillates through 

 a few inches. It appears from Mr. Lloyd's paper {Phil. Trans, of 1831) that the 

 mean level at Sheerness is higher in spring tides than in neap tides by seven inches 

 nearly; also there seems to be no doubt (as shown by Mr. Whewell, Phil. Trans., 

 1839 and 1840) that the mean level increases as the moon's declination increases, 

 amounting to three inclics at Plymouth, when the moon's declination is 25° ; at- 

 Petropaulofsk and Novo-Arkhangelsk the mean level rises as the moon's declina- 

 tion increases. 



The use of the soundings intended to furnish corrections to the readings of the 

 pulley-gauge is in many cases a doubtful remedy, on account of the continued change 

 in the zero of the wiieel's index; in fact, it would have required numerous soundings 

 at other hours than noon. As it is, a combination of the corrections by enveloping 

 curves and soundings had to be adopted. Thus, for December 5th, soundings at 

 noon 43.0 feet (see record further on), mean level 36.6, hence reading of scale at 

 noon 6.4; reading of pulley-gauge at that hour 19.0, correction by curve — 12.5, 

 corrected reading 6.5, which agrees with the first number; this is, however, a very 

 favorable case. For intermediate hours the correction as given by the curves serve 

 as guides. The reduction to the same level afi'ects the times generally very little. 



The following table contains the soundings taken at noon between the interval 

 of the first and second series, those taken during the series being given in the 

 record. 



Soundings at Noon. 



' For the past ten days the tide register has not been reliable on account of the rope slipping. 



