A. MATHEMATICS AND ASTRONOMY. 57 



orbit from that of the modern comet, especially because of 

 the disturbance experienced by the attraction of the planet 

 Jupiter; but allowing for this disturbance, Klinkerfues con- 

 cludes that probably the comet which was seen in the year 

 1162 w^as identical with it, and was also intimately connected 

 Avitli the shower of meteors known to have been observed in 

 the year 524. 19 (7, 1873, 214. 



THE PEIilE VERTICAL TRANSIT INSTRUMENT AT LISBON. . 



It is well known that the transit instrument, when used in 

 the prime vertical, has in the hands of Struve led to the 

 most accurate possible determinations of the zenith distance 

 of the stars and the constants of stellar aberration, nutation, 

 and parallax. The investigation of parallax is, of all others, 

 the most delicate that ens^asfes the attention of the astron- 

 omer. It was, therefore, with great interest that Struve gave 

 to the government of Portugal his advice when consulted, in 

 1861, in regard to the new observatory that was then about 

 to be erected at Lisbon. The geographical position of the 

 Royal Observatory at Tapada was to be such that the bright 

 star Alpha Lyrse must pass near its zenith every day at its 

 transit, and Struve represented the great value that would 

 attach to a thorough investigation of the parallax of this star, 

 to which purpose he knew of no instrument so well adapted 

 as the prime vertical transit. The labor of using this instru- 

 ment is so considerable, and the advantage of a thorough 

 familiarity with the methods of so expert an observer as 

 Struve was so highly esteemed, that the Portuguese govern- 

 ment dispatched to St. Petersburg a young officer of the 

 navy. Lieutenant Oom, whose duty it should be to perfect 

 himself in practical astronomy at the renowned observatory 

 of which Struve was the director. The new observatory at 

 Lisbon contains, besides the prime vertical, also a magnifi- 

 cent equatorial and an excellent meridian circle. While 

 each of these instruments is, in its way, of the most perfect 

 construction, yet especial interest centres in the prime verti- 

 cal transit. This has been manufactured by the famous 

 artists, the brothers Repsold, of Hamburg, who have intro- 

 duced into its construction several novel features. Upon a 

 solid pedestal of stone there stands a pier of iron, manufact- 

 ured at the great establishment of Krupp. On this pier the 



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