ASTRONOMY. 355 



"Mr. Downing read a second paper upon the ]i. A.'s of the Cape cata- 

 logues of 1850 and 1880. He has compared the E. A.'s of the catalogue 

 of 1850 with those of the catalogue of 184:0, those of the catalogue of 

 1880 with the Melbourne catalogue for 1870, and with the Cape cata- 

 logue for 1860. The results of the Cape for 1850 and 1880 have thus 

 been referred to the mean of three other catalogues (Melbourne, 1870 ; 

 Cape, 1840 and 1860). Mr. Downing's conclusion is that the discord- 

 ances between the two Cape catalogues for 1850 and 1880 should not be 

 laid to the account of the latter catalogue. There is an error of O^-l 

 at 140O polar distance." {Bull. Astron., May, 1885.) 



JS'ew methods of determining the co-ordinates of polars without the 

 necessity of knowing the instrumc7ital constants. — According to the usual 

 method the instrumental constants are determined by supposing the 

 co-ordinates of one or two polars to be known ; these coordinates are 

 corrected from time to time by the combination of all the available 

 pairs of observations separated from each other by twelve hours ; these 

 pairs of observations are, however, rather rare. If the star observed is 

 situated very near the pole, the circle that it describes in its diurnal 

 motion will be entirely comprised within the field of the telescope, and 

 evidently observations of the star's position, separated by four hours, 

 for example, may take the place of those separated by twelve hours. 

 . M. Loewy gives formulae, by whose aid two observations separated 

 by an interval of four hours may be taken, and certain geometrical con- 

 ditions indicated by his theory being complied with the whole efitect of 

 the instrumental errors may be eliminated. The co-ordinates of polars 

 may be thus determined with a higli degree of precision and quite in- 

 dependently of the level, azimuth, and collimation errors, as well as of 

 the flexure and division errors,. (Btill. Astron., August, 1885.) 



Inaccuracies due to the use of the usual formula) in the reduction of 

 polar stars. A method of observing polars at any distance from the meri- 

 dian. — "It is sometimes convenient to observe circumpolar stars when 

 off the meridian ; the ordinary reduction may then lead to erroneous 

 results. M. Lcewy introduces a simi)le corrective term, by employing 

 which the desired accuracy may be attained ; the computation is facili- 

 tated by a numerical table annexed to the memoir." {Bull. Astron., April, 

 1885.) 



Star- charts. — In the Vierteljahrsschrift for 1884 Herr Palisa, in speak- 

 ing of the publication of Dr. C. H. F. Peters's celestial charts, enters into 

 some interesting details concerning the different processes employed in 

 the construction of charts to be used in searching for minor planets. 

 He speaks briefly of the very appreciable differences between Dr. 

 Peters's estimates of magnitude and those of other observers when the 

 stars under consideration are below the tenth magnitude. Thus Dr. 

 Peters's eleventh magnitude stars are called twelfth and thirteenth mag- 



