Dreyer — On Astronomical Transit Observations. 521 



do not depend on instrumental circumstances, but really on the 

 observer's individuality, can be proved in several ways. Altbough. 

 Schonfeld observed with an annular micrometer, whose construction, 

 certainly, may give rise to constant errors, it is impossible in this way 

 to explain the differences between Schonfeld and the other observers 

 of nebulae. Schmidt observed also with an annular micrometer, and 

 still his observations differ about as much from Schonfeld' s, as those 

 of Schultz, made with a wire-micrometer. Between the right ascen- 

 sions obtained with nearly equal telescopes, and by means of wire- 

 micrometers in Leipzig and Upsala, I found, besides, a difference 

 (Yogel- Schultz): 



Aa cos 8 = - 0^-10,*'' 



which agrees very well with the difference between the equations 

 Schonfeld -Schultz and Schonfeld - Yogel = -0^-34 - (-0^-21)=- 0=-13. 

 But the second series of Schonfeld' s observations, published only a few 

 months ago, have made the reality of the influence of the observer's indi- 

 viduality quite unquestionable. This series contains 153 objects, which 

 also occur in Schultz' s observations, and the author has himself com- 

 pared their E.A.s with those in Schultz's "Preliminary Catalogue of 

 ]S'ebul8e,"t which is less troublesome than the way of comparing chosen 

 by me. The result is : | 



Aa cos S = - 0^-150, 

 while a comparison between this series and the lii'st one gave 

 I. -II. --0^-21. 



These two comparisons agree most perfectly with my result given 

 above, and show with certainty that Schonfeld, being aware of the 

 fact that he made his right ascensions too small, or was inclined to 

 observe transits of nebulae too soon, in the course of years has altered 

 his method of estimating the latter. This proves to some extent that 

 the personal error is not perfectly independent of the individual's will, 

 which must be considered as one of the most important results we 

 hitherto have found respecting this abstruse subject. 



My examination of Schultz's observations has given another 

 result, which also, I think, is of some importance. Julius Schmidt 

 had already, by comparing his own observations with those of 

 Schonfeld, found the equation to be different according to the con- 



* From fifty-five identical differences : nebiila star. I have already mentioned 

 this equation, as -w-ell as the preceding one, in a re-view of Dr. Schultz's work ia 

 the Vierteljahrsschrift der Astronomischen Gesellschaft, x., pp. 64-73. 



t Monthly Notices of the R. Astron. Society, xxxv., p. 135. 



% Astronomische Beobachtungen aiif der Stemwarte zii Mannheim, ii Carlsruhe 

 1875, p. 8. 



