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inaccurate theodolite, which did not allow to read beyond ful} 
minutes, I had at my disposal only a sextant. Recently however, 
after consulting with Dr. E. F. van pe SANDE BAKHUIJZEN who 
for a long time already has rendered me valuable assistance in my 
endeavours to obtain useful results, I have bought a portable uni- 
versal instrument, by means of which I hope that my future obser- 
vations will attain a higher degree of accuracy. 
Yet, among the earlier observations there are already some, of 
which the publication may prove desirable, with a view to the great 
uncertainty which still exists about the exact position of several 
places on the South-West coast of Africa. 
I will here communicate my observations for the determination 
of the latitude of Ambriz and of San Salvador, both in Portuguese 
West-Africa. 
I. Determination of the latitude of Ambriz. 
The observations were made with a sextaut of WEGENER with 
vernier on which can be read 10", and an artificial horizon ; besides 
I used a mean time chronometer. Observations referred to the sea- 
horizon, together with some made by means of the small theodolite 
mentioned above, are not communicated, because they are far less 
accurate. 
The errors of graduation of the sextant were determined by 
Dr. Karser at Leiden as follows: 
at 0° 0"0 at 70° + 22"5 
10 + 5.5 80 + 23.5 
20 + 9.5 90 + 24.0 
30 +-19:0 100 4 24.5 
40 + 16.0 110 + 24.5 
50 + 18.7 120 + 24.5 
60 Se OLY 
Before each set of observations I tested the adjustment of the mirrors 
and the telescope. If smal! deviations were found, they were imme- 
diately corrected. The index error was always determined before the 
observations by 4 till 6 pointings on the direct images; in the case 
of solar observations they were equally distributed over both limbs. 
This determination was often repeated in the same manner after 
the observations. 
I assumed for the eastern longitude 13° 8' or expressed in time 
52 m. 32 sec. This value was deduced from determinations of 
