DORPAT AND POULKOVA. 389 



Repsolds, Bmuer and others. Tbesc Lave found tlicir most frequent use in con- 

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

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

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

 ment of an arc of latitude of 25°, and one of longitude of 69°. The fonner we 

 iTave 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 ste})S for continuing this work ten degrees fiu-ther south- 

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

 ment that of an arc of longitude naturally f(:irced itself upon Struve's attention 

 as a necessary 8up})lemental undertaking, and he had al read}', in 1848, prepared 

 the way by enlisting the interests of Genera! Wrontschenko, then engaged in 

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

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

 failed of execution, Otto Struve in 1860 proposed the meastu'ement of an arc 

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

 mountains. This work will lie lirought to a close this present summer — the future 

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

 confidently expected. The Rep sold Port ahlc Vertical Cirde has been used in the 

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

 PortaUe Extra-mcridmial 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. AVe may, then, soon expect from 

 this grand operation valuable additions to our knowledge of the ciu'vature of 

 the European portion of the earth's surface. The portable instruments alluded 

 to merit more than a passing allusion. The Repsold Circle has been made the 

 subject of an elaborate monograph by Smyssloft'; a short notice of its construc- 

 tion and performance will be found in Silliman's Ameiican 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 Brauer 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 JMeridian, for which 

 pm'pose nothing can be desired more convenient than the formulae given by Dollen 

 in his memoir entitled "Die Leitbestimmung," &c., "The determination of the 

 time bv 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 Russian 

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

 is used. Each 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 which a base is measm-ed couipares favorably with that 

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

 believe, been called in question. One of the most interesting operations per- 

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

 bars used in other countries. This \Aork, conducted during the interval 18o0-54, 

 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 Appa- 

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

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

 na^^an meridian arc. This apparatus may be defined as Bessel's synnnetrical 

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



