of the Transit Instrument, 4(51 



free from Error. The mean places of the Forty-six Stars are 

 deduced from the Catalogue published in the Nautical Al- 

 manac for 1823; and, for the Convenience of the Observer, 

 the Declinations have been added. The daily Right Ascension 

 of the Pole-star is that, given by Dr. Struve, and is the same 

 as was lately published by Mr. Baily : it has been added, 

 from a Conviction of its Utility. 



Before I conclude, let me impress upon the young Astronomer, 

 the absolute necessity, of his observing as often as possible, the 

 Transits of the Stars forming the Maskelynean Catalogue; 

 by the mean of several of these, the Error of Observation will 

 be confined indeed within narrow Limits ; — the Error of the 

 Clock well ascertained, and any Deviation of the Instrument 

 from its Meridian immediately detected. To this Catalogue 

 he stands indebted, for his Original Accuracy, and to it he 

 may safely trust his Future. Each Star he may consider a 

 Guide to his Instrument, and a Zero to his Clock ; and, 

 taken collectively. They will afford him a meridian mark, 

 of which ALONE it may be said, Non imber edax, non 



AQUILO IMPOTENS, P0S8IT DIRUERE. 



Blackman-street, January 1, 1821. 



P.S. In observing, it will be found convenient to place the Five 

 Observations of every Star, under each other, prefixing the 

 Hour and Minute to that of the Meridian Wire only ; the Ob- 

 server will then readily obtain the Mean Transit, by adding 

 together the Seconds, multiplying the sum by Two, cutting off the 

 Two Figures to the right as Decimals, and adding or subtracts 

 ing 12, 24, or 36, to, or from, those on the left; and in some 

 Instances doubling the sum of the Seconds will, without 

 further Trouble, give the Transit over the Meridian Wire. 



Oil and Quicksilver have been alluded to, as affording good 

 Reflecting Surfaces ; they are, however, apt to collect Dust, 

 but which may be easily separated by passing the former 

 through Bibulous Paper, aad by pressing the latter through 

 folds of Linen. 



