Dreyer — On Astronomical Transit Observations. 



505 



across all the wires. The transits look, of course, as if seen in a 

 <;ommon broken telescope, "^^"e take as examples--' : — 



EoGEKSOIf - DrxKix. 



1852. 



D. east. 



Stars. 



D. west. 



Stars. 



Jan. 23, 

 April 2, 

 April 26, 



- 0^-69 

 -0-89 

 -0-65 



4 

 3 

 3 



- 0^-52 

 -0-47 

 -0-21 



4 

 3 

 3 





Dtotki. 



S" - Ellis. 





1853. 



D. east. 



Stars. 



D. west. 



Stars. 



Oct. 14, 

 Oct. 20, 

 Nov. 9, 



O'-OO 

 -0 -01 

 -0 -08 



3 

 3 

 3 



-0=-21 

 -0 -17 

 -0 -19 



3 

 3 

 3 



"We hare now seen from a great number of instances that the diffe- 

 rent direction of the motion has no influence on the personal error in 

 observations of artificial stars, but that the different position of an 

 instrument with a broken telescope often has a very considerable 

 influence on the estimation of the transits. It is impossible to explain 

 this otherwise than by supposing the existence of a disturbing ciixum- 

 stance in the instrument itself. Already, eight or nine years ago, it 

 was suggested, for instance, at the conference in Berlin, 1867, on the 

 European measurement of arcs of meridian, that such a disturbance 

 might arise from an eccentiic illumination, causing an apparent 

 shifting of the whole system of wires. The above-quoted observations, 

 taken with the instrument of the Leipzig Observatory before and after 

 the change of the illumination, show clearly how great an influence 

 this had had. The matter was, however, not yet sufiSciently examined, 

 as long as it was unknown why the influence of the illumination was 

 a diflerent one for different observers. But the determinations of 

 longitudes, which, during the last few years, were undertaken in Swit- 

 zerland, have thrown light on these phenomena, and the investigations 

 of Messrs. Plantamour, Hii'sch, and Rudolph "Wolf have considerably 

 elucidated the question about the constancy of the personal error. 



These three astronomers have taken the obseiwations for the said de- 

 terminations of longitude. The personal equation of the two first-men- 

 tioned was several times determined in the course of the years 1868 to 

 1870, and varied but little. But it was found in August, 1867, in 

 Zurich, that the equation (Hirsch - R. Wolf) was now quite different to 



* GreenTvich Observations, 1852 and 18-53 (inti-od.) 



