On the Error discovered in the Nautical Almanac. 377 



take into which that statement may tend to lead them, as 

 well as the illiberal insinuation which it tends to throw upon 

 the French astronomers and mathematicians, by challenging 

 theni with an unjust adoption of the results derived from 

 the Nautical Almanac, into tlieir Co?inuissance des Terns, 

 under the mask of pretended originality, has given occasiou 

 to the production of this article ; a circumstance which, 

 from a long residence at the Royal Observatory, and of 

 course a more familiar acquaintance with the habits of the 

 late Dr. Maskelyne, I may be conceived to be better able to 

 answer than others less acquainted with that justly celebrated 

 man. 



Dr. Maskelyne savs, in his preface to the Nautical Al- 

 manac of the year above alluded to, that he has taken the 

 mean obliquiiv of the ecliptic for the beginning of the year 

 at 23° 27' 43", 8, which he reduces to the apparent obliquity 

 by applying ihe equation arising from the precession of the 

 equinoxes, combined with a diminution of halt a second a 

 year from a chance of this quantity in the plane of the obli- 

 quity itself, and an equation depending on the place of the 

 moon's node arising from her action on the spheroidal figure 

 of the earth :— these two equations are, as Dr. Maskelyne 

 states, contained in two tables which were published at the 

 same time with the first volume of the Greenwich Obser- 

 vations. The first equation amounts to — 0",5, and the 

 second to — 9",0; tlieir sum is — 9",5 which applied to 

 23° 27' 43", 3, the mean obliquity above mentioned, gives the 

 apparent obliquity of the ecliptic 23° 27' 33'',8 at the be- 

 ginning of 1802. 



By comparing this deduction with that given opposite 

 the first page of the Nautical Almanac, it will be found ex- 

 actly the same. 



The obliquity of the ecliptic at the beginning of tlie pre- 

 cedinsi year, viz. 1811, Dr. Maskelyne states in the preface 

 of the Nautical Alman:ic to be 23" 27' .5l"9, and at the be- 

 gimiing of the year i813 b.e takes it to be 23° 27' 5r',3 ; so 

 that the mean f)bliqaitv of the ecliptic at the begmning of 

 1812, It should appear from these two statements, ought to be 

 Q.V' 27' 51", 6, instead of 23'^ 27' 43^3 as mentioned in the 

 Almanac tor that yeir. This apparent discrepancy mak- 

 ing a diftlrence of 8",?, may seem to give sanction to the 

 account contauicd in the Philosophical Magazine of last 

 month, that itie diflferencc in question might have probably 

 originated in mistake. Dr. iMaskelyne was however by far 

 too caret'iil a man to suflcr such a circumstance to have 

 escaped his notice ; and the frequent use of the obliquity of 

 the ecliptic in the calculations that were constantly carrying 



on 



