( 279 ) 
Il. Determination of the latitwle of Chiloango from circum- 
meridian altitudes. 
To determine the latitude of Chiloango a great number of obser- 
vations of circummeridian altitudes of stars have been made. For these 
observations the vertical circle was turned successively in different 
positions and in each position one or more pairs of stars were 
observed, each consisting of a northern and a southern star culmi- 
_ nating as near as possible (within a few degrees) at the same zenith 
distance. In this way we already eliminate in each position of the 
circle besides the flexure of the telescope a great part of the periodic 
division errors, while the influence of the latter, especially to be 
feared with a small instrument, is further diminished by the combi- 
nation of the different positions. 
At first observations were made in the 4 positions, indicated by 
zenith-point O°, 90°, 180° and 270°; of these however the 1st and 
3rd, and also the 2ud and 4 bring the same divisions under the 
two microscopes. After this the two positions 225° and 135° were 
added. But before the observations in the last position had com- 
pletely succeeded, I resolved to start an entirely new series of 
observations, consisting of the 4 positions 0°, 45°, 90° and 135°, 
which moreover allowed me to improve upon the arrangement of 
the observations themselves. 
Hence my observations may be divided into two series. 'The second 
series by its arrangement would seem to be the more accurate; it 
was found however, that the weight of the first series was not so 
much less. Therefore I have only rejected my very first observations, 
and of the later ones only those where the pointings had succeeded in 
one position of the instrument only. 
I now proceed to describe the arrangement of my observations. 
The star was always bisected by the horizontal middle thread, or 
in the position the reticule had before February 1901, alternately 
by the two horizontal threads. Near the meridian the pointings 
were made by means of the screw for slow motion ; but whenever 
possible I let the star come on the thread by its own motion and 
determined the moment of bisection. The readings were always made 
with each of the two microscopes on the preceding and on the 
following division. Care has always been taken that the bubble 
of the alidade level did not deviate more than three divisions from 
the middle; in the second series the deviations were generally even 
smaller and were equalised as much as possible in the two positions 
Us) 
Proceedings Royal Acad. Amsterdam. Vol. IV. 
