o8j DORPAT AND POULKOVA 



order to prosecute telescopic spectrum investigations, the appriTittns for wliich 

 was received in 1S66 from Donati. 



The Hcliomctcr, made hy Merz and Mahler, in the eastern dome, for want of 

 an observer could not be brought into continuous use nntil 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 of results, but 

 it was also best to await the result of the further experience of Bessel, Wich- 

 man and Johnson, before deciding to trust so complicated an instrument in 

 delicate investigations. Possibly Dr. Auwer's study in 1861-62 of the heliome- 

 ter used by Bessel confirmed the decision to use the Ponlkova instrument for 

 other purposes 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 measurement of large relative distances. From 1S58 to 1864 this tele- 

 scope has been used by l)r. Winnecke in photometrical measurements and in 

 observations upon the several comets, as also upon tlic 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 Ilcfractor, made by Baader, in the western dome, has been princi- 

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



The Prime Vcrlkal Transit, made by 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 minimum influence of abeiTation and parallax, and the restilts 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 inter- 

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

 bably be soon published. In iS61-'G3 this instrument was used by Lieutenant 

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

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

 59° ''.G', 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 relati^■e declinations of certain double stars as preparatory 

 to an extended series in which the subjects of ]-elative and absolute parallax, 

 aberration and periodicity of latitude should be simultaneously investigated. 



To the Meridian Circle, made by Rcpscld, 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 until 1854, assisted in the interval — 1844 and 1849 — by 

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

 vati<jns of the comparison stars of Biela's comet. The catalogue work was con- 

 tinued by Winnecke from 1858 imtil 1S64 ; in 1866 its further continuation was 

 assigned to Mr. Gromadski, whose diligence in filling up the man}^ g'fips 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 number 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 pi;blished 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 



