270 Proceedings of the Royal Irish Academy. 



shows not to give results in accordance with estimates made by the 

 method of sequences, or by comparison with artificial stars of measure- 

 able brilliancy." 



Some astronomers lay great stress on the use of a photometer in the 

 determination of star magnitudes, but the Cordoba observations given 

 in Dr. Gould's great work, the JJranometria Argentina, show what good 

 results can be obtained by careful estimation with the naked eye, aided 

 when necessary by an opera-glass, without the use of any photometer 

 whatever. With reference to this method, Sir John Hcrschel says 

 [Cape. Ohs., p. 305): ""Without dissuading from the new and the im- 

 provement of old instrumental contrivances (or astrometers) for this 

 purpose, and having myself attempted it, not as I think without some 

 degree of success, as will be hereafter explained, I am yet disposed to 

 rely mainly for the formation of a real scale of magnitudes on com- 

 parisons made by the unassisted judgment of the naked eye." 



Of the photometers which have been tried for the purpose, the 

 '' wedge photometer," as used by Prof essor Pritchard, seems to give the 

 most consistent and satisfactory results. A simple and ingenious form 

 of photometer has lately been devised by the Eev. T. E. Espin, a de- 

 scription of which will be found in the English Mechanic, vol. xxxvii., 

 p. 384. 



I have added Professor Pritchard's magnitudes — obtained with the 

 " wedge photometer " — of those of his stars which are included in my 

 Catalogue. They represent the magnitudes of the stars as supposed to 

 be seen in the zenith, and this fact should be remembered when his 

 magnitudes are compared with those given by other astronomers. 



Professor Pritchard's results will be found in vol. xlvii, of the 

 R.A.S. Memoirs. 



The magnitude given in the Harvard Photometry have also been 

 added, and are denoted by the letters H. P. 



I have inserted in the Catalogue on my own authority a number of 

 stars which I have suspected of variation, either from my own ob- 

 servations or from the great discrepancies in the magnitudes assigned 

 to them by different observers. 



The positions of the stars have been brought up to 1880-0 (the 

 epoch of Mr. Proctor's Atlas), the R.A. being given to the nearest 

 second, and the Declination to the nearest decimal of a minute. 



In conclusion, my best thanks are due to the Eev. T. E. Espin, 

 B.A., F.E.A.S., President of the Liverpool Astronomical Society, and 

 W. S. Pranks, Esq., E.E.A.S., Leicester, for much valuable assistance 

 and information. 



