On Errors in the Nautical Mmanac. 35 



1817; and has arisen (I presume) from an error in Lalande's 

 Tables at the end of the first volume of his Astronomy, p. 250, 

 where the Argument C is erroneously stated 3000 too great, in 

 the mean conjuuctions from 1812 to 1820; an error which has 

 been carefully avoided by Mr. Vince in his edition. 



Whilst I am upon the subject of the Nautical Almanac, may 

 I be allowed to as>k whether any of your readers can inform me 

 why the very excellent and useful preface which usually accom- 

 panies that work, has been omitted by the present Astronomer 

 Royal, in the publications for the years 1817 and 1818. The 

 tables from which that work is computed have been successively 

 improved ; and an account of the same, together with a state- 

 ment of the tables used by the com|Hiters for the time being, has 

 been hitherto preserved in the preface above alluded to. But a 

 person who may now be desirous of ascertaining the correctness 

 of any of the calculations, would be at a loss to know to what 

 tables he should refer. This is the more to be regretted, as it is 

 notorious that there is a considerable variance with correspond- 

 ing calculations in other similar works. 



For exam]jle, the times of new and full moon, as given in the 

 Nautical Almanac, and in the Connaissance dcs Terns, for the 

 present year, differ frequently (after allowing for the difference 

 of meridians) many minutes, and oftentimes many hours from 

 each other. This inequality in the results must, however, be 

 attributed to some other source than the use of a different set of 

 tables ; all of which boast of considerable accuracy: yet, as it 

 shows the necessity of a computation from the tables themselves, 

 when any nice calculation is required, the knowledge of the 

 identical ta])Ies made use of in the formation of the ephemeris, 

 might lead to a detection of the error ; as we have already seen 

 in the case of .Jupiter's satellites. 



I shall not, however, intrude further on your indulgence, at 

 present ; my object being merely to call the attention of your 

 readers (who may have more leisure) to an investigation of the 

 subject : and I shall be happy if it be the means of correcting 

 any errors which at present exist, or which in future may be likely 

 to occur in those truly valuable works. 



I am, sir. 



Your obedient servant, 



July 21, 1816. ASTRONOMICUS. 



C 2 Xni. Ex' 



