3 §8 DORP AT AND POULKOVA. 



The reduction of tLe "eye and era-'' observations having shown that the 

 Houth-AVctzer clock in the west room, and the Kessel's normal clock originally 

 placed in the central rotunda, were aflected hy the unavoidable changes of temper- 

 ature, the former was replaced in 1861 by a dial connected by electricity with the 

 normal clock, thus avoiding the laborious comparisons by chronometer that had 

 been nntil that time earned on daily. In order to secure a still more uniform 

 temperature the normal clock was then placed in an inner vault underneatli the 

 rotunda, Avliere the daily thermomctric term in the clock rate is quite impercep- 

 tible. Since 1SG2 the observations have been recorded upon a Krille's chrono- 

 graph, which stands iri a warmed room adjacent to the observing room, and differs 

 fronr those in common use in America principally' in that the observer's pen is 

 independent of the neighboring clock pen, and in having a very convenient 

 arrangement by A\hicli the observer at the transit can at will stop the revolving 

 cvlinder or set it in motion again. The clock automatic circuit-breaker is that 

 of Krille. It consists of a thin vertical slip of mica at the extremity of a short 

 arm attached at right angles to the upper portion of the penduliun, and in thei)lane 

 of vibration ; at every second the mica cuts through a small horizontal thread 

 of mercury through which the electric current is passing. The Muston mean tiuie 

 clock was in 1866 connected with the central telegraph station in St. Peters- 

 burg, and regulates several sympathetic clocks. A noonday signal is also auto- 

 matically given. 



The exquisite small Meridian Transit, made by Brauer, and now foimd in an 

 appropriate l)uilding southwest of the larger observatory, was used in the longi- 

 tude expeditions to Dorpat, Moscow, &c., and has been employed by Fritsche 

 in the series of lunar observations recently published by him in the liulletin of 

 the St. Petersburg Academy. A mate to this fine instrument is to be found at 

 tlie naval observatory at Cronstadt. The five-inch Stelnheil objective, mounted 

 in 1866 parallactically in the east dome of the small auxiliary observatory erected 

 in 1863, 100 yards south of the principal one, is intended to be used by 

 Wagner in an investigation into the relative parallaxes of some of the brighter 

 stars. The evidences of the extraordinary accuracy attained with the Meridian 

 Transit are such as to justify the expectation that very decisive results will ensue 

 from this renewal of the method so lately applied hy Auwers to the determina- 

 tion of the parallax of 34 Groombridge. 



The celestial photometry which has remained until lately in so crude a state, 

 thanks to the labors of Steinheil, Sci;»lel, and Zollucr, promises in future to rank 

 as an exact science. An ingenious Photometer^ invented and made by Professor 

 Sclnverd, of Speyer, was mounted in 1866 by Messrs. Smyssloff and Berg in the 

 west dome of the auxilliary observatory, and offers a fine opportunity for research 

 in a field that has as yet been but too little cultivated. A mate to tliis unique 

 instrument has been ordered for the observatory of Bonn by Professor Arge- 

 lander, who has signified his intention of devoting his future years to its use. 



A little to the northeast of the central building is the convenient and tasteful 

 observatory erected at the expense of the military academy, and furnished with 

 a clock, a fixed transit, and very many portable instruments, together with very 

 convenient arrangements for their use. This structure, completed in 1857, is of 

 course exclusively for the use of the officers of the geodetic division of the Nicolas 

 Military Academy whilst pursuing at Poulkova their course in practical astron- 

 omy. Among the A\orks executed by these officers under Dollens's directions are 

 several whose results may be looked for with general interest, such as the twelve 

 repetitions of the measurement of a short base line, in the year 1865, and the 

 observations made in 1866 for the investigation of the local attraction of the 

 plumb line in the neigiiborhood of Poulkova. 



In recoimting the larger fixed instruments of the Central Observatory, we must 

 not omit a few words concerning the smaller portable ones, of which the insti- 

 tution possesses several fine specimens of the best workmanship of Ertel, the 



