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DORPAT AND POULKOVA. 389 



Repsolds, Braucr and others. These have found their most frequent use in con- 

 nection with the geographic and geodetic labors conducted by its astronomers, 

 of which we shall only mention the two grand international undertakings that 

 have not as j'ct been surpassed in their magnitude — we refer to tlie measure- 

 ment of an arc of latitude of 25°, and one of longitude of 69'^. The former we 

 have already frequently mentioned as being a work intimately connected with 

 the foundation and the history of the first 25 years of the observatory's exist- 

 ence. The preliminary steps for continuing this work ten degrees further south- 

 ward to the island of Crete are now being taken. To this meridian measure- 

 ment that of an arc of longitude naturaliy f\>rced itself upfin Struve's attention 

 as a necessary supplemental undertaking, and he liad already, in 1848, prepared 

 the way by enlisting the interests of General Wrontschenko, then engaged in 

 the triangulation of the soathern part of Russia. This original project of a 

 meastuement along the 47th parallel, as proposed by Struve in 1857, having 

 failed of execution, Otto Struve in ISGO priqjosed the measurement of an arc 

 from Valentia, in Ireland, eastward to Orsk, at the southern end of the Ural 

 mountains. This work will be brought to a close this present summer — the future 

 further prolongation of the line through Narvaul and Irkutsk to Nicolaieff may be 

 confidently expected. The Ilepsold Portable Vertical Circle has been used in the 

 latitude determinations on this measurement of an arc of longitude ; the Braucr 

 Portable Extra-meridional Transit has been adopted for the telegraphic longitude 

 determinations, all of the latter being made by two observers, Dr. Thiele of 

 Bonn and Captain Jalinski of Poulkova. The instruments, as well as the observ- 

 ers, exchange places during the season's work. We may, then, soon expect from 

 this grand operation valuable additions to our knowledge of the curvature of 

 the Emopean portion of the earth's surface. Tlie portable instruments alluded 

 to merit more than a passing allusion. The lve})Sold Circle has been made the 

 subject of an elaborate monograph by .Smysslotf; a short notice of its construc- 

 tion and performance will be found in Silliman's American Journal for 1867. 

 The Brauer's Transit has not as yet been similarly brought to public notice ; this 

 is owing to the fact that the few (six) that have been made by Braucr have been 

 in continual use since they left his hands, but it is promised that this neglect 

 shall be remedied ere long. These instruments, constructed at Poulkova at 

 Dollen's suggestion, are specially adapted to use out of the iMeridian, for which 

 purpose nothing can be desired more convenient than the fornnila? given by Dollen 

 in his memoir entitled '' Die Leitbestimmung,'' &c., " 'V\\q determination of the 

 time by means of a portable transit instrument established in the vertical of the 

 Pole Star. St. Petersburg, 1863." 



In connection with geodesy we must not omit to notice the Base-measuring 

 Apparatus used in Struve's work, and now generally adopted by the Itussiau 

 geodesists. This is distinguished by its simplicity and the facility with which it 

 is used, liiich piece is a plain bar of iron furnished at one end with a touch lever 

 and enclosed in a packing of cotton within its wooden case ; two interior ther- 

 mometers and a reversible level complete the apparatus. With such means the 

 rapidity and ease with vvhich a base is measured coujpares favorably with that 

 attained in other countries, and the accuracy of the results have never as yet, we 

 ]>elieve, been called in question. One of the most interesting operations per- 

 formed in connection with this base apparatus was the comparison with specimen 

 bars used in other countries. This work, conducted during the interval 1850-54, 

 has only been surpassed in magnitude by the more recent comparisons made at 

 Southampton. 



Among the geodetic apparatus worthy of special mention is the Pendulum xippa- 

 ratus made by the Ilepsokls for the Central Observatory, and used since 1864 by 

 Professor Sawitsch, Avho proposes to visit all the stations of the Russo-Scandi- 

 navian meridian arc. This apparatus ma}' be defined as Bessel's symmetrical 

 pendulum with reciprocal axes, being constructed according to the views of thai 



