386 DORP AT AND POULKOVA. 



order to prosecute telescopic spectrum investigations, tbe apparatus for wliich 

 was received in 1866 from Donati. 



The Ileliometer, made by Merz and Mahler, in the eastern dome, for want of 

 an observer could not be brought into continuous use until quite recently. Not 

 only was this delay caused by the necessity of making several much-needed 

 instrumental changes tending to convenience of use and accuracy uf results, but 

 it was also best to await the result of the further expeiience of Bcssel, Wich- 

 nian and Johnson, before deciding to trust so complicated an iustnmieut in 

 delicate investigations. Possibly Dr. Auwer's study in 1861-6:2 of the heliome- 

 ter used by Bessel confirmed the decision to use the Poulkova instiTiment for 

 other pui-jjoses than that for which it was originally intended ; and certainly the 

 reported valuable results recently obtained by Rutherford in stellar photography 

 assure us that probably this method will advantageously replace the heliometric 

 for the measm-ement of large relative distances. From 1858 to 1864 this tele- 

 scope has been used by Dr. Winnecke in photometrical measurements and in 

 observations upon the several comets, as also upon the conjunction of Venus and 

 Jupiter in 1859. Since 1864 Mr. Fritsche has made use of it in the observa- 

 tions of several asteroids. 



The Small Befradofj made by Baader, in the western dome, has been princi- 

 pally used in the observation of coiuets, asteroids, and occultations. 



The Prime Vertical Transit, made V)y Repsold,in the south wing, was used until 

 the end of 1842 by Struve himself on the series for the determination of the 

 constant of aberration. Seven stars were observed upon at the periods of maxi- 

 mum and mininnun influence of aberration and parallax, and the results are pub- 

 lished in his well-known memoir. Observations on three of these stars were con- 

 tinued for the determination of the constant of nutation ; the series being iater- 

 Tupted in 1856 by Struve's illness, was continued by Otto Struve, and will pro- 

 bably be soon published. In 1861-'63 this instrument was used by Lieutenant 

 'Oom, (now director of the lloyal Observatory at Lisbon,) in determining the 

 zenith distances of about 80 stars whose declinations are between 57° 46' and 

 • 59° ^.6', each star being observed at least four times. After the determination of 

 .aberration and nutation, the proper use of this instrument is found in the inves- 

 tigation of absolute annual parallax ; accordingly, in 1866 it was used in the 

 determination of the relative declinations of certain double stars as preparatory 

 to an extended series in which the su])jects of relative and absolute parallax, 

 abeiTation and periodicity of latitude should be simultaneously investigated. 



To the Meridian Circle, made by Ilepsold,in the east room, was assigned the 

 observations for a catalogue of 3,755 stars, including all of the sixth magnitude 

 north of 15° of south declination. This work was begun in 1841 by Sabler, 

 and continued by him ruUil 1854, assisted in the iiiter\-al — 1844 and 1849 — by 

 Dollen. In the years 1853-56 Sabler and Lindhagen were occupied in obser- 

 vations of the comparison stars of Biela's comet. The catalogue work was con- 

 tinued by Winnecke from 1858 until 1864 : in 1866 its further continuation was 

 -assigned to Mr. Gromadski, whose diligence in filling up the man}'^ g'^^ps caused by 

 the unfavorable weather of the winter months and the twilight of the summer, 

 .authorize the belief that the completion of the series is soon to be looked for. 

 The nttmber of stars that will have been observed with the meridian circle will 

 be greater by 1,500 than that of the catalogue originally contemplated ; the 

 reduction of this series of observations has been delayed more than that of any 

 other undertaken by the observatory. It is intended that each star shall be 

 observed in the two positions of the circles and of the interchangeable ocular 

 and objective. The ptiblished results of Sabler's and Lindhagen's observations, 

 .as given in Gould's Astronomical Journal, and those of Winnecke made at 

 the opposition of Mars in 1862, give assurance of the high value that the cata- 

 logue will have when published. With this instrument will be made the deter- 

 minations of the positions of the 500 stars to be used as fundamentals in the 



