Discovery of an Error in the Nautical Almanac. 53 



the proper boundarv of prudence: but certainly in the pre- 

 sent case Dr. Kelly is most completely mistaken ; tor I can 

 confidently affirm, that Mr. Groombriclge knew no move of 

 what I had written on the subject before it appeared in 

 print, than did Dr. K-elly himself. But as the Doctor has 

 allowed me a right, 1 shall take an opportunity of occa- 

 sionally referring to Mr. Groon)bridoe's letter, not only be- 

 cause it has been considered a partnership production; but 

 also because, from our long and iniiuiate acquaintance, we 

 have had frequent opportunities of communicating our 

 thoughts on astronomical subjects. It was in one of these 

 communications that Mr. Groombridge noticed to me the 

 discrepancy in the quantity of the obliquity of the ecliptic as 

 contained in the Nautical Almanac of 1812, from those of 

 other years ; and my remarks upon it were, that the uncer- 

 tainty'arising from the observations of the Greenwich qua- 

 drant were such, as to render the quantity of that datum 

 doubtful to manv seconds. In confirmation of this state- 

 ment, I shall once more call the attention of your readers to 

 the paper which I published in the Philosophical Magazine 

 of December 1810; and although f noticed this paper in 

 my remarks upon the subject in question, I have good rea- 

 son to believe Dr. Kelly has not given himself the trouble 

 to read it; or, if he has read it, he has not thought proper 

 to notice it, probably in consequence of its militating against 

 his own supposed discovery. 1 shall therefore copy so 

 much as relates to the present occasion, which runs thus : 

 " If we look to the account given in the Lunar Tables, pub- 

 lished by the Board of Longitude in France, we shall find 

 those tables were compikd principally from the astrono- 

 mical observations made in the Royal Observatory at Green- 

 wich ; and not only the epocha, but the present state of 

 diminution in the obliquity of the ecliptic has been in a 

 great measure determined from them. Weshall not therefore 

 be surprised to find hereafter a nearer coincidence in the 

 actual state of the ancient observations, and the deductions 

 drawn from theory, when we possess, as we hope soon lo^ 

 do, the means of settling this epocha, and actual state of 

 diminution at the present period. The grand mural circle 

 now making for the Royal Observatory by Mr. Troughion, 

 will, it is expected, be in readiness for observation early in 

 the ensuing year; and we cannot doubt but the first object 

 to be determined with it, will be the settling the above- 

 mentioned data, so essential in the theory and practice of 

 astronomy." I f 1 had not been at the lime* above menioned 



» Eight months hcfore the paper was published which gave rise to (he 

 present cominuincation. D3 acquainted 



