DORPAT AND POULKOVA. 385 



The activitj^ of tlio Central Observatory has doubtless suffered somewhat from 

 the restricted communication between Poulkova and the neighboring cities, St. 

 Petersburg and Tsarskoe-Selo. For, however much this isolation favors the 

 undisturbed prosecution ol" observations and study, it imposes a dreaded inonot- 

 onv upon the lives of the non-astronomical portion of the community, from the 

 efi'ects of which the astronomers themselves cannot be entirely free. To coun- 

 teract the influence of this sameness — so prejudicial to mental and ph^'sical 

 health, and so detrimental to the harmony of society — requires the constant 

 attention of each individual living at the observatory. It uill thus be easily 

 understood that the personal example and the ihlluence of the director asaman,^ 

 no less than liis experience as an astronomer, are needed in order to secure the 

 happiest ^vorking of all the parts. Possibly the sameness of the social circle 

 exaggerates the influence of the monotony of the astronomical "work, for there is 

 in Poulkova no rotation of duties, such as in some other observatories atiurdb a 

 slight relief to the members of the corps. 



It was in accordance with Struve's foresight that the efforts of the observatory 

 to realize its general object, "the advancement of astronomy as a science,''' 

 should be principally confined to stellar astronomy, and that to each astronomer 

 should be assigned the instnunents needed for the work undertaken by him, 

 and for whose execution he is responsible, thus reversing a very common prac- 

 tice of assigning the observer to an instrument. The description of the instru- 

 ments and the mode of using them ma}^ be found fully given in the well knowu' 

 "Description de I'observatoire." The following condensed notice of the progress 

 of the works there indicated as having been begun Avill perhaps have interest. 

 The Great Befntcfor, made by Frauenhofer, in the central dome, has, since its 

 erection, been used principally by the present director. The general survey in. 

 1841 of the northern heavens, requiring the examination of 17,000 stars, and 

 leading to the discovery of nearly 500 new double stars, has been already men- 

 tioned. Up to the present time micrometric ol)servations (jf relative ])o:jitions- 

 have been made upon ] ,200 doul)le stars, which will probably be published in 

 1S69 in all their details. Struve's method of observing position angles, /. c.,, 

 by placing the two parallel threads of his micrometer so that the space iiicl;uled 

 between tliem is bisected by a line joining the two stars, leads probably to tlie 

 interesting systematic errors in observed angles of position, investigated by hiiii. 

 in 1852-56, and again in 1866, by observations upon artificial double stars. 

 In the latter year an investigation was also made of the errors of estimated, 

 small distances, and a simple systematic correction deduced, by which these 

 l)ecome as valuable as actual measurements with the micrometer. Nine opticallv 

 double stars have been made the subjects of special investigations for relative 

 parallax. The determinations of relative positions of comets and faint com- 

 parison stars have next claimed attention. The series upon the Biela's, Faye's^ 

 and Donati's comets, and those of 1861 and 1865-66, are to be specially men- 

 tioned, as also the fruitless search after Biela's comet at its late predicted return. 

 The observations of Neptune's satellite and the determination of the planets' 

 mass have been already mentioned ; a large number of observations upon the 

 satellites of Uranus and Neptune still await publication. The occultations of the 

 Pleiades, in which a dozen observers sometimes combine, have been regularly 

 continued. The study of Saturn's rings and of the great nebula in Orion have 

 also claimed attention whenever circumstances have conspired to favor the pros- 

 ecution of these very delicate observations. The results already attained, and 

 their comparison with those of the Bonds at Cambridge, are already well known 

 to the -world. The instrumental changes made in the great refractor have been 

 quite insignificant ; but on account of increasing unsteadiness in the parallactic 

 movement the director has proposed to replace the clock-'\\ ork by some one of 

 the improved mechanisms now made. This will become the more necessary ir 

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