Astronomy. 77 



of triangulation in which everything rested upon distances alone, 

 and each night's work could be rendered independent of all 

 changes of scale value due to temperature and other causes. 

 Four stars were selected near the outer limits of the group form- 

 ing angles of a quadrilateral nearly enclosing it. Outside of these 

 and nearly in the extension each way of the diagonals of the 

 quadrilateral four other stars were selected, and the positions of 

 these latter were determined by meridian instruments at other 

 observatories. The two lines of stars furnished the means of 

 determining scale values and deducing absolute positions. 



The distances of each star from the four angles of the funda- 

 mental quadrilateral were then measured, and these distances 

 furnished equations for correcting assumed star places and scale 

 values. The scale values were also independently determined by 

 measures of the " Cygnus arc," a series of stars used for the same 

 purpose in the transit of Venus observations. 



These two series of observations were reduced, the resulting 

 places compared with each other, and hence definitive places of 

 the stars deduced for the epoch 1885 - 0. 



The Konigsberg measures of distances have been known to re- 

 quire changes by reason of errors of assumed scale values and 

 temperature corrections. A new T reduction of these measures is 

 given by Dr. Elkin, and a revised table of places for the Bessel 

 stars deduced for 1 885*0 for comparison with the Yale places. 

 The probable errors of the differences Y. K. are computed, the 

 mean value being 0"-20. Dr. Elkin considers twice this amount, 

 or ±0"'40, as a fair value to adopt, inside of 'which the actual 

 motions are so likely to be mixed up with the errors of observa- 

 tion as to afford little clue to their real amount .or direction. 

 Above this limit of twice the probable error, if its estimate be 

 correct, the large majority of the discrepancies are due to actual 

 displacements. Of fifty-one stars compared nineteen fall below 

 the limit 0"*40, while of thirty-two there is some considerable 

 probability of displacement since 1840. A chart showing the 

 apparent displacements is given, and Dr. Elkin says : 



"The first fact which strikes the attention on examining these 

 values of Y. — K. is, that for the six largest there is a remarkable 

 community of direction and amount ; these stars, shown on the 

 chart with broken lines, are as follows : 



// // // 



No. 14 Displacement in a : -1-43, in <5 : +2-15, total: 2'52 



+ 1-28 2-T6 



+ 1-32 1-78 



+ 1-16 2-01 



+ 2-23 2 54 



+ 1-19 '2-12 



and it is remarkable that this general direction of drift is very 

 similar to the reversed absolute motion of Alcyone as given by 

 Newcomb, namely, for forty-five years : 



// // // 



Eeversed motions of Alcyone from ) . .„„ . , , „ .„ , . v „ „, 



Newcomb's Zodiacal Catalogue: [ in a ; -°' 92 ' 1Uf5; +247 ' total: 2 ' 61 



14 



Displacement in a : 



- 1-43, 



17 





-2-67 



21 





—1-31 



26 





— 1-80 



35 





— 1-32 



36 





— 1-91 



