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LIV. Queries relative to the Mode of using M. ScmrMACHER's 

 Tables of Aberration aud Nutation. 



To the Editors of the Philosophical Magazine and Journal. 



Tj^ VERY lover of asti'onomy must feel obliged to your cor- 

 -*--^ respondent, Mr, F. Baily, for the many valuable commu- 

 nications with which he continues from time to time to enrich 

 your pages. The Supplemental Table in your last Number, 

 which, in conjunction with others of M. Schumacher, serves 

 for computing the precession and nutation of a number of 

 fixt stars, will doubtless be duly appreciated by those ob- 

 servers who are enabled to avail themselves of the assistance 

 it offers. I am sorry to say, that at present I am not among 

 that number. Owing to my imperfect knowledge of the Ger- 

 man language, I am not certain that I imderstand the account 

 the author has given of the formation of these tables ; and as 

 he has added no example of the manner in which they are to 

 be used, I feel considerable doubt as to the method of apply- 

 ing them in particular cases : for instance, it is customaiy in 

 using tables of this kind, in leap-years, to add one day before 

 the 29th of February, or to subtract one after. Is this the 

 case here ? Again ; Do the tables give the corrections for the 

 noon of each day ? But another, and more perplexing doubt 

 arises, as to the days themselves. The tables profess to give 

 the logarithms necessary for finding the corrections for every 

 tenth day; that is, for January 0, 10, 20, &c. But what is 

 meant by January 0? If it mean the instant that the year 

 commences, or the beginning of January the 1st, then I pre- 

 sume that 10 is to be accounted the lltli; and so on. I ob- 

 serve that in the table of apparent right ascension of the prin- 

 cipal stars in Mr. Baily's Astronomical Tables for 1822; in 

 M. Schumacher's Astronomische Hiilfstqfeln, and also in our 

 Nautical Ephemeris, the same notation prevails. The latter 

 work, for instance, gives us a table of the true apparent place 

 of twenty-four fixed stars, at the moment of noon on every 

 tenth day of the year, beginnhig with January 0. What day, 

 I again ask, is here meant? In the explanation prefixed to 

 the Ephemeris, we are told that the places of the planets, sun, 

 &c. with the particulars depending upon them, are computed 

 to the instant of apparent noon, or beginning of each day : — 

 Hence, if I want the sun's place for the instant the year begins, 

 I find it opposite Januaiy 1. Why is a different notation 

 used for the stars ? Or, if January 1 is to be understood to 

 mean the instant the year begins, what am I to understand 

 by January 0? Would Mr. Baily have the goodness to ex- 

 plain 



