Royal Astronomical Society. 229 



consequence of Mr. Wrottesley's frequent and continued absence 

 from home, the task of observing and computing chiefly fell, and 

 who has executed this task with extraordinary zeal, skill, and fi- 

 delity. 



J 1 1. On the Projection of Maps and Charts. By Professor Littrow. 



Three kinds of projections are chiefly had recourse to in the 

 construction of maps, — the orthographic, the stereographic, and 

 tlie central. The object of Professor Littrow is to deduce the ge- 

 neral properties of these three principal projections, which, though 

 they differ from each other in no other respect than in the situation 

 of the eye and perspective plane, with regard to the principal circles 

 of the sphere, have hitherto been always treated as distinct and in- 

 dependent problems. 



The concluding part of the memoir contains some general re- 

 marks on the solutions of the general problem by Gauss and La- 

 grange ; and a demonstration that Gauss's formulae (contained in a 

 memoir a translation of which appeared in Phil. Mag. and Annals, 

 N.S., for August and September 1828,) are comprehended in those 

 of Lagrange, the latter being only particular values of the former. 



IV. On the construction of the Hour-lines of Sun Dials. By 

 Professor Littrow. 



V. On the Formulae for the computation of Precession. By 

 M. Mattheus Valento do Conto, Director of the Observatory at 

 Lisbon. 



VL Notice of a forthcoming work on the Measures of Double 

 Stars. By Professor Struve. 



Professor Struve hoped, in June last, to complete his extended 

 catalogue of double stars, containing all the observations made since 

 those already published in his well-known Catalogus Stellarum 

 Duplicium, Dorpat, 1827 (or from 1824 to 1836). This last-men- 

 tioned catalogue contained 3112 stars; from which the professor 

 has, for various reasons assigned, excluded ^QO, and has added 64 

 remarkable new ones of greater distance than 32", and 21 of less 

 distance. The number of stars, therefore, is 2707. The measures 

 were made with a wire- micrometer applied to the large refractor, 

 with a power varying from 320 to 1000, and mostly in an illuminated 

 field. Calling each night's observations of one star a measure, the 

 number of measures is about 11,000, or, on an average, four to each 

 star. 



Professor Struve has divided these stars into eight classes (Sir 

 W. Herschel used four), as follows : 

 W. 1 

 I. 0'' to 4' 



n. 4 ^ 8 



III. 8—16 



IV. 16 — 32 — 



