ASTEONOMY. 433 



double stars. MM. Henry have been occupied with astronomical pho- 

 tography during the year, and, as is well known, with great success; 

 various clusters of stars have been photographed, and M. IMouchez ap- 

 pends to his report a reproduction by heliogravure of a plate of the 

 great clusters in Perseus. A trace of the motion of the minor planet 

 Pallas was shown after an exposure of thirty-five minutes. The im- 

 portant results obtained by MM. Henry in photographing very small 

 stars in those crowded parts- of the heavens where the galaxy crosses 

 the ecliptic have been already referred to. - - - Steady progress 

 has been made, both with the calculations and printing of the Paris 

 Catalogue of Stars, and it is expected that the first volume of both series 

 (star positions as observed, and catalogue) will be completed by the 

 end of the year. Vol. 18 of the Memoires is finished. The report further 

 details the })ersonal work of the members of the observatory staff. 

 Amongst the additions to the museum is a portrait of Pons, presented 

 by M. Tempel. 



The report for the year 1884 is preceded by one which enters spe- 

 cially into the present condition of a scheme for removing the principal 

 instruments in the observatory to a site where not only greater steadi- 

 ness can be secured in their mounting, but where the objections of be- 

 ing surrounded by a great city will not exist. It appears that the 

 Academy of Sciences have not, so far, favored this scheme. M. Mouchez 

 states very clearly his view of the question. (Nature.) 



Potsdam. — Researches are in progress on a new determination of the 

 wave-lengths of a large number (300) of the Praunhofer liues; on the 

 influence of temperature on the refraction and dispersion indices of 

 fixed substances; on the reflective power of various substances; on 

 the absorption-spectra of such substances as are used in photography, 

 &c. 



Jupiter and Mars were regularly observed and the nebulae observa- 

 tions are concluded. 



The photometric measures embraced long series of determinations of 

 the brightness of the major planets and of seven of the asteroids. 

 Many variable and red stars were also measured. Determinations of 

 the brightness of stars by photography have also been made, and a 

 number of photographs of clusters have been taken. 



"The first part of the fourth volume of the publications of this obser- 

 vatory, which was published in the latter part of last year [1885] con- 

 tains three papers. The first of these is by Professor Vogel, and con- 

 tains the observations which he made with the great Vienna reflector 

 in 1883 for the purpose of testing the performance of the great object- 

 glass. Professor Vogel's final verdict is altogether favorable. 'Tlie 

 Vienna objective,' he says, 'leaves nothing to be desired as regards the 

 precision of the images,' and he speaks of using with advantage a power 

 even of 1,.500 upon planetary markings, a statement which is illustrated 

 by a sketch of part of Saturn's ring as seeu with that miignifying power. 

 H. Mis. 15 28 



