458 Astronomical Society. 



considerable as has been the pains bestowed on them, tliey are all 

 so far surpassed by this work of Mr. Bally, that it ought rather to 

 be considered as belonging to a new class, than to be compared in 

 any way with preceding ones, which must eventually all be super- 

 seded by it*. 



It is time now to speak more particularly of the Catalogue itself. 

 Its whole plan and arrangement, the selection of the stars, the pre- 

 paration and revision of tlie formulae, the choice of the coefficients, 

 and the discussion of the terms to be retained or rejected, we owe 

 to Mr. Baily, who has stated every particular relating to it in a 

 most elaborate Preface, which may indeed be regarded as a com- 

 pendium of all that is known on the subject of the corrections, and 

 is remarkable at once for its precision and perspicuity. A great 

 portion of the computation has been gratuitously performed by Mr. 

 Stratford, checked by a computer engaged for that purpose. From 

 this very severe labour, however, he was unfortunately compelled 

 to desist, I regret to say by ill health, and his place supplied by a 

 professional computer: but the hardly less laborious task of com- 

 paring and checking the computations of his assistants, and, what is 

 as important in all such cases as accuracy of computation, the care- 

 ful superintendence of the press, and repeated revision of the whole 

 work, has entirely devolved on him ; and never, I must say, was 

 task performed with more diligence and exactness. 



The selection of the stars has been made from the Catalogues of 

 Flamsteed, Bradley, Lacaiile, Mayer, Piazzi and Zach, so as to in- 

 clude all stars down to the .5th magnitude, wheresoever situated in 

 the heavens,— all of the 6th within 30° of the equator, and all the 

 stars to the 7th magnitude inclusive, within 10° of the ecliptic. Al- 

 most all of them, however, are to be found in the Catalogues of 

 Bradley or Piazzi, from which they have been reduced to 1830, 

 (the epoch adopted) by formulae given by Bessel. Their number 

 is so considerable, that in whatever part of the heavens we may be 

 observing, one or more are sure to be within a moderate distance ; 

 so that no one provided with this Catalogue can possibly be at a io.ss 

 for a zero-point to check his observations, and ascertain the state 

 of adjustment of his instrument. To its convenience and utility in 

 this respect, I can speak from individual experience. It is indeed 

 become my sheet anchor, and has infused into a series of observa- 

 tions wholly dependent on such aid, a degree of exactness which, 

 without it, I should hardly have expected to attain. 



The formulae employed for calculating the corrections are almost 

 entirely those of Bessel, who has laboured with such diligence and 

 perseverance on this department of Astronomy, as to make the sub- 

 ject almost his own. In adopting them, however, Mr. Baily has 

 taken nothing for granted, even from such high authority. He has 

 gone over the whole subject anew; and the slight inaccuracies which 



* From this sentence, however, I ought to except special tables for the 

 daily reduction of a certain number of select stars, whose use is no way su- 

 perseded by the general Catalogue, being destined for continual, as the 

 latter is only for occasional, reference. 



the 



