160 Parallax of 61 2 Cygni, deduced from 



(12.) Pritchard — Researches in Stellar Parallax by the aid of 

 Photography, from Observations made at the Oxford University 

 Observatory, Oxford, 1889. 



In the formation of Table XXIII, giving the various values of the parallax 

 of 61 Cygni hitherto published, I have not placed Pritchard's values in bold 

 type, because they cannot be regarded as trustworthy. They have been dis- 

 carded in taking the means of the determinations for 6i l and <5/ 2 . I have ex- 

 amined the eight sets of normal equations given in the work on 61 Cygni 

 (pages 17-63) and among the eight sets have not found one which is correct in 

 every quantity. The set on page 30 first attracted my attention and so it may 

 be used for illustration. As given there the quantities are : 



— i // .3i4o = + 88.0000 x — 6.7889 dp — 2.5442 7r 

 + 4 .3827 = — 6.7889 +8.4762 +9.7965 

 + 17 .1716 = — 2.5442 +9.7965 +38.7724 



These should be : 



— i // .2i8o = + SS.0000 x — 6.7889 dji — 0.9281 n 

 + 4 .3853 = — 6.7889 +8.4783 +9.7854 

 -I-17 .1967 = — 0.9281 4.9.7854 +38.7849 



This criticism applies not only to the normals for 61 Cygni but for many 

 of the other stars as well. No attempt has been made to verify all the num- 

 bers in each set of normals, nor indeed to extend the test to all sets of normals 

 given in the book, but it can be stated that at least one number is wrong in 

 each of the fourteen sets given on pages 17, 23, 30, 36, 47, 52, 58, 73, 75, 87, 

 104, 106, 107 and 113. 



(13.) Davis — Contributions from the Observatory of Columbia 

 University, New York, No. 13. 



(14.) Wilsing — Untersuchungen iiber die Parallaxe und die 

 Eigenbewegung von 61 Cygni nach Photographischen Aufnahmen. 

 Publicationen des Astrophysikalischen Observatoriums zu Pots- 

 dam, No. 36, pages 152 and 148. 



(15.) Rambaut — On the Effects of Atmospheric Dispersion on 

 the Position of a Star. Monthly Notices, Vol. LV, page 123. 



(16.) Flint — Research Work at the Washburn Observatory. 

 The Astrophysical Journal, Vol. VI, page 420. 



A preliminary announcement of results now in process of computation. 



(17.) Kapteyn — Bestimmung von 250 Parallaxen. Astronom- 

 ische Nachrichten, Bd. 145, S. 300. 



