A. MATHEMATICS AND ASTRONOMY. 45 



and the observations have been most easily made in the 

 8th order spectrum in the second of these, or in the 5th order 

 with the third. 



The spectra are viewed by reflection from the surface of 

 the orating, and to separate the spectra of the higher orders 

 a 45 prism is placed between the grating and the observing 

 telescope. By this ingenious process these spectra are sepa- 

 rated, the red of the 6th order spectrum falling below the 

 yellow of the 7th, and this underneath the green of the 8th ; 

 while above this green lies the blue of the 9th order, and 

 above that the extreme violet of the 10th. 



Tliis separation may be effected by the direct-vision prism 

 of the observing telescope, but less perfectly. 4 D^ June^ 

 1876,429. 



THE THIRD EADCLIFFE CATALOGUE OF STARS. 



We learn from the report for 1876 of the Rev. Robert 

 Main, Radcliffe observer at Oxford, that the preliminary work 

 for the compilation of the Third Radcliffe Catalogue has 

 been begun. It will contain about 4000 stars, the result of 

 nine years' (1862-1870 inclusive) observations. Particular 

 attention has been given to those stars of the British Associ- 

 ation Catalogue whose positions are imperfectly determined. 



For the year June, 1875, to June, 1876, there were observed 

 2303 transits and 3471 zenith distances of 1187 stars. The 

 sun was observed on the meridian 100 times, the moon 51 

 times. Mercury 34 times, Fe?w<s 17 times. Mars 5 times, Ju- 

 piter 24 times, Saturn 14 times, Uranus 5 times, and Ne2> 

 tune twice. 



LUNAR MAPS. 



Besides the well-known map of Beer and Madler, there 

 have been several attempts to portray the features of the 

 moon's surface. Of these no one is probably more accurate 

 than that of Lohrmann, a portion of which was published in 

 fine steel engraving in 1824. Barth, of Leipzig, is now pub- 

 lishing the remainder of this map, which will be three feet 

 in diameter. A descriptive letter-press is to be furnished by 

 Schmidt, of Athens. At the same time Schmidt is editing 

 his own work, which will be embodied in a map six French 

 feet in diameter, which the Prussian government has pur- 



