DORPAT AND POULKOVA. 387 



new review of the heavens lately undertaken by the German Astit)nomical Asso- 

 ciation. 



The spirit of investigation inculcated by Struve asks for the simplest instru- 

 ments and the smallest ones consistent 'W'ith optical power, and demands the 

 most laborious watchfulness over the instrumental errors, together with such 

 a symmetrical arrangement of the obseixations as to necessitate only the simplest 

 possible assumptions with regard to the unknown or suspected sources of eiTor. 

 These principles have possil)ly increased the labor and somewhat retarded the 

 completion of the work assigned to the meridian circle, but have had a still more 

 decided influence upon the progress of the work undertaken Avith the two prin- 

 cipal meridian instruments. These stand in the west room, and some of the 

 results attained by them are alreadj'^ known through the memoirs of Lindhagen 

 and Peters. 



The Vertical Circle, made by Ertel, standing on the west side of the obsemng 

 room, was used by Peters until 1849, in observations for latitude and the declina- 

 tions of about 350 bright stars. The determination of latitude has been already 

 published in a memoir previously cited, as also has been the special series in which 

 the absolute parallaxes of the stars Polaris, a Aurigse, e Ursae JMajoris, Groombridge, 

 1830, a Bootis, a Lyrse, a Cygni, 61 Cygni, were investigated. Dr. Gylden's 

 refraction tables for Poulkova, deduced from Peters's observations, were pub- 

 lished in 1865 ; the entire series of observations previous to 1849 will probably 

 be published within three years as a complete work, ahhough the places of a 

 number of stars in the original catalogue remain undetermined. From 1849 to 

 1863, the vertical circle was used by Dollen principally for observ'ations of the 

 sun, and in determinations of the declinations of stars used in the geodesic work of 

 the Russian sui'veys. Since 1863 Dr. Gylden has Avith this instrument du^ected his 

 attention towards the standard stars of the Berlin and British almanacs ; some 

 observations upon Venus, made at her superior conjunction in 1865, are valuable 

 as afiordiug strong negative testimony on the question of the solar atmosphere ; 

 equally interesting are the thorough investigations made into the errors of the 

 meteorological instruments used in connection with the vertical circle, and into 

 the law of the decrease of temperature with increasing altitude above the earth's 

 surface. 



The Principal Meridian Transit, made by Ertel, at the east end of the west 

 observing room, was designed, in connection with the Kessel nonnal clock, not 

 only to give the time to the rest of tlie observatory, but also for the determination 

 of the absolute right ascensions of some 300 fundamental stars ; this latter num- 

 ber was increased to 400, and the prescribed series of observations was substan- 

 tially finislied in 1853. A preliminaiy series specially directed to the circnmpo- 

 lar stars had been made by Peters in 1840. New piers having been provided, 

 the two meridian marks established, and the normal clock received, obseiwations 

 on the fundamental catalogue were begun b}^ Schweizer and continued by him 

 from 1842 to 1844; by Fuss from 1844 to"^1847; by Lindhagen from 1847 to 

 1850; by Wagner fi-om 1850 to 1857. In 1855 and 1856 the transit was 

 u^ed by Lindelof in determining the right ascensions of stars used in the lon- 

 gitude expeditions. In 1S60 the instrument was given into the hands of Mr. 

 Brauer, the successor of Pohrt as the observatory instrument maker ; several 

 changes, hicluding the regrinding of the pivots, were then made, and in 1865 the 

 objective was mounted upon three points in order if possible to secure greater 

 constancy in the collimation error. Since 1860 the redetermination of the 400 

 fundamental right ascensions has been undertaken by Wagner, and the series 

 will probably be completed before 1870. The reduction of the observations 

 previous to 1853, and the compilation of the resulting catalogue, are now finished ; 

 their publication may be looked for in the present year. The reduction of the 

 second series (made with the transit since its improvement by Mr. Brauer, and 

 recorded chi-onographically) progresses with the observations. 



