Dreyek — On Astronomical Transit Observations. 



503 



moving along the line from left to right, under an angle of 45° and of 

 315° with the horizon, taken in Leyden and in Berlin, have given no 

 difference at all between the two directions.* 



The result of all observations with time-collimators seems to be, 

 that it is never of any great importance in which direction the artifi- 

 cial star goes, as the difference in the estimation never exceeds a 

 few hundreths of a second. If such a difference really exists (as in 

 C. Wolf), it must arise from an unsymmetrical arrangement of the 

 fibres of the nerves in the retina of the eye ; and Wolf really found, by 

 looking at two dots of ink, made on a piece of paper, at equal distances 

 from both sides of a straight line, that the space between the line and 

 the right dot always seemed to him, if he looked at it with the right 

 eye, a little larger than the space between the line and the left dot. 

 This experiment shows that he would always fancy the space between 

 the wire in the telescope and a star to the right of it to be larger than 

 it really was. 



I>ut in perfect opposition to these results were many observations 

 of real transits, with broken telescopes, as by these differences of consi- 

 derable size were often found. Weiss, for instance, remarked, in 1863, 

 by reducing the observations for determining the longitude Leipzig - 

 Dabletz, that the clock corrections were different, according to the 

 position of the instrument. He and Bruhns found the following mean 

 differences :f — 



Obs. East minus Obs. West. 



"Weiss. Bruhns. 



Eye and Ear - 0^-17 + 0^-07 



Chrongr. -0-21 -0-10 ' 



The variation of the personal error with the position of the instru- 

 ment (circle west and observer east, or circle east and observer west) 

 may be seen by the following examples which are found in Dr. 

 Albrecht's book about determinations of longitude (pp. 21-2). The 

 observations were made by the chronograph, each observation com- 

 prising 5 wires : — 



1. Tkai^sit Instetjment in Leipzig, 25th Mauch, 1867. 



Albrecht - Valentiner. 



West. 



-0^-33 

 -0-39 



East. 



+ 08-45 

 + 0-49 



West — East. 



-0 -88 



Each numher is the mean result from 7-9 stars. 



* The ohservations are given in Albrecht's Bestimmung von Langendili'erenzen^ 

 Leipzig, 1869, p. 20. 



t. Astr. Nachrichten, bcviii.. No. 1668. 



