70 Royal Astronomical Society. 



since Groombridge made his observations is sufficient to detect and 

 exhibit proper motions, Mr. Johnson undertook to re-observe the 

 Catalogue with great care, and has now nearly completed the task. 



The north polar distances have almost all been redetermined, and 

 a large portion of the right ascensions ; there are, however, several 

 gaps, occasioned by the necessity of observing certain circumpolar 

 stars for meridian error, and fundamental stars for clock error. The 

 increased number of well-determined stars will now allow the ob- 

 server more liberty in this respect, and the blanks are rapidly filling up. 



Besides the general advantage of a full standard catalogue of stars 

 within 50° of the north pole (which by the aid of Groombridge's de- 

 terminations may be carried forwards for some years), and the ma- 

 terials thus afforded for investigating precession, proper motion, &c., 

 a special advantage will be found in geodesical operations from this 

 large supply of accurate places for the zenith sector*. 



Mr. Johnson expects very soon to receive the heliometer by Rep- 

 sold, when his attention will be directed to another department of 

 practical astronomy. Thus limited in time, and having the aid of 

 only one assistant, he has been induced to confine himself in most 

 cases to Uvo observations of a star in the same year, and occasionally 

 to one. The star has, however, been observed in different years, so 

 that there is a considerable check on errors of computation and on 

 casual fluctuations in the instruments. 



Care has generally been taken to note circumstances of interest 

 connected with stars, which have come under observation. Among 

 others, their magnitudes have been watched with much attention. 

 The method adopted has been simply to estimate the apparent mag- 

 nitudes in reference to ideal standards ; and pending the discovery of 

 some more accurate photometric measure, Mr. Johnson has instituted 

 an inquiry as to the degree of reliance which may be placed on the 

 method he has pursued. This inquiry has not yet been fully followed 

 out ; but the results, as far as they go, are given in the preface to 

 the present volume. From what is there said, it may be inferred 

 that Mr. Johnson would recommend that at every observation of a 

 star, not distinctly visible to the naked eye, an estimate of its mag- 

 nitude should be noted, unless there is some obvious impediment to 

 a correct determination ; and that a mean of such estimates should 

 be taken as the magnitude of any given star, just as the mean of a 

 number of observations in right ascension or north polar distance is 

 considered as the correct right ascension or north polar distance. 



Mr. Johnson acknowledges the great services which he has hi- 



* It is proper to remind observers who possess instruments not of the 

 highest class, or who cannot afford the time for deducing fundamental 

 places, that the partial catalogues in the Radcliffe Observations will supply 

 them abundantly with zone stars, from the pole to 50° of north polar di- 

 stance, and that the volumes of the Edinburgh Observations will afford a 

 sufficient number of similar stars for a complete zodiacal catalogue. With 

 these and the Greenwich catalogues there can be no want of a sound base 

 of operations. Professor Argelander has made excellent use of the Rad- 

 cliffe Observations in his admirable Zone Observations. 



