14 



NINTH REPORT— 1839. 



26° as 57 : 58 by measure on the sheet, and as 57 : 60 by the 

 law of the squares ; differing only ^^^th from the law. 



In hope of throwing some light on the question of the best 

 anterior epoch of decimation, considered separately from paral- 

 lax, I arranged the numerical errors, or residue of calculated 

 times for 1837 and 1838, keeping the increasing and decreasing 

 declinations separate, but not distinguishing north declinations 

 from south. I was not, however, able in this way to perceive 

 how any change in the declination epoch would be attended with 

 advantage. 



An arrangement of the numerical errors in the calculated 

 times for 1837 into two parcels for each month, those following 

 a north transit in one parcel, and those following a south transit 

 in the other, gave the following results : — 



1837. 

 Month. 



Mean Error of calculated 



time of H. W. following a 



• North Transit. 



Mean Error of calculated. 



time of H. W. following a 



South Transit. 



Dock Observations. 



Dock Observations. 





min. 



3-7 too early. 

 2 '4 ditto. 

 1-6 ditto. 

 2-3 ditto. 

 2-0 ditto. 

 1-9 ditto. 

 1-4 ditto. 

 3-0 ditto. 

 2-3 ditto. 

 2-5 ditto. 

 1-6 ditto. 

 2-3 ditto. 



min. 



37 too late. 

 2-4 ditto. 

 1-6 ditto. 

 2-3 ditto. 

 2-0 ditto. 

 1-9 ditto. 

 1 -4 ditto. 

 3-0 ditto. 

 2-3 ditto. 

 2-5 ditto. 

 1-6 ditto. 

 2-3 ditto. 



February 



March 



April 



May 



June 



July 





September 



October 







1 



The average of the year gives the observed time of the H.W. 

 following a north transit, 2*2 minutes later than the mean or 

 calculated time ; and of the H. W. following a south transit, 2*2 

 min. earlier than tlie mean. 



It is quite certain that the diurnal inequality in the intervals 

 at Bristol is such as to make the time of a H.W. next after a 

 north transit, in the main, later than that of a H. W. next after 

 a south transit. This is evident upon the slightest inspection 

 of sheets 37 to 43 tide-gauge observations. 



The effect of this constant of diurnal inequality is positive 

 when the moon's declination (four days anterior) is north ; and 

 negative when it is south ; or, in other words, the diurnal in- 

 equality in the interval is greatest when the moon has [had] 



