( 280 ) 
of the instrument. This was much facilitated by the stability of the 
mounting. 
As already stated before, the pointings have always been made 
in the two positions of the instrument, and though the zenith-point 
has also been determined a few times by means of the harbour-light, 
the results thus obtained have not been used in the computation. 
On an average a complete observation consists of 5 pointings in each 
position; a few times clouds prevented me from making more than 
two. In the first series the instrument was usually reversed only 
once in the middle of the observation, in the second series the 
pointings were made alternately in both positions. Symmetry with 
respect to the meridian was secured as much as possible and I never 
observed in hour angles greater than 30 min. 
For the reduction of my observations all microscope readings were 
first corrected for the error of runs. The amount of this error was 
always derived from all the observations of the night, and the 
required corrections were computed by means of small tables. 
For the level correction, the value of a division could always be 
taken = 5'.40. 
The reduction to the meridian was computed by means of the 
usual development in series; it was always sufficient to retain only 
the terms depending on sin?4¢ and sin*}¢. The refractions were 
computed from CaiLuert’s tables in the Connaissance des Temps ; 
afterwards small corrections have been applied to reduce them to the 
tables of Rapau. The barometric pressure was read on an aneroid, 
of which the correction for a temperature of + 25° amounts to 
— 1.5 mM. as derived from a comparison with a barometer of 
Furss. Except in one case (z = 62°) the zenith distances at which 
the observations were made lie between 40° and 60°. The star 
places are taken from the Nautical Almanac and therefore rest on 
the catalogue of NEWCOMB. 
As an example I give here the original data for one observation 
and choose therefor out of the second series the first at which six 
pairs of pointings were made, viz. that of /? Crucis on May 31. The 
first column of the following table gives the positions of the in- 
strument designated by PR and LZ as the telescope and circle were 
either to the right or to the ieft of the observer at the ocular, the 
second column gives the chronometer times of the pointings; the 
third and fourth give the readings of the two divisions at micros- 
cope A, the fifth and sixth give the same for microscope B, the 
seventh gives the readings of the level. 
