60 . 



the effect of this can be but small. The effect however from this 

 cause must be somewhat greater in the Greenwich Catalogue, be- , 

 cause the observations made there are reduced by Bradley's Formula 

 of Refraction, in which the allowance for change of temperature is 

 not conformable to experiment. On the other hand, taking the 

 place of the equinox as in the Greenwich Cat. the quantity of the. 

 motion of the ecliptic on the equator will be nmch reduced, which, 

 circumstance is greatly in favour of the R. ascensions of that Cata-, 

 logue. By adopting the computations of Mr. Bessel on Bradley's 

 observations we are enabled to compare my Catalogue in right 

 ascension with the Catalogues of Maskelyne in 1770 and in 1805, 

 and of Piazzi in 1800. The result is very encouraging, because it 

 appears to prove that the places of the principal fixed Stars have 

 been determined at different periods during the last sixty years witli, 

 considerable exactness, and consequently we may expect to be able 

 sooner to avail ourselves of future observations in investigating 

 several points of importance relative to the fixed Stars. ,r,i 



i The Catalogue of Dr. Maskelyne of 1770 differs from mine, re- 

 duced to 1770 in its mean quantity only by 0",07 m time in right 

 ascension, and by 0," 17 in North Polar distance. , .,.0 



f The Catalogue of Piazzi of 1800 differs from mine only in its 

 mean quantity by 0'',04 in right ascension, and by 0",16 in N. Polar 

 dist. :-J-::-.- .-:..;.:-..,:.,:■;■.:•-.;;.. :, - .. . 



-The Cat. df Maskelyne of 1805 differs from mine in its mean 

 quantity by 0^04 in right ascension. 



The close agreement of the respective Stars of the Cat. of I8O0 

 in right ascension with mine is particularly deserving of notice, and 

 it ought I think to be kept in mind, that this Catalogue of Dr, 

 Maskelyne was made only a few years before his death with the old 

 Transit Instrument and the Mural Quadrant of the Observatory ^/ 

 Greenwich. 



