536 
We have always tried to choose the two stars for one evening 
in such a way that their absolute zenith-distances would not be 
too great and almost equal, in order to practically eliminate from 
the result of each evening the flexure of the instrument and the 
systematic division-errors of the circle. We have been fairly success- 
ful in this and find : ) 
Z ZN — ZS Mean (ZN — Zg ) 
Jidda 1st series 37° to 56° 3° to + 4° — 1°.5 
se Pel AE —4 , +2 i 
Mecea 23 + 44 —7 , +2 —2 0 
while one evening only the zenithdistance bas exceeded 45°. 
Both the chronometers employed in the observations (as well as 
the Leroy-watches) had been regulated after mean solar time, and 
so their readings, after having been corrected, had still to be reduced 
to sidereal time. In all our calculations account was taken of course 
of the variation of sidereal time at mean noon with the longitude. 
The pointings were mostly arranged fairly symmetrically with 
regard to the meridian. The reduction to the meridian was computed 
with the aid of AtLsBrecuT’s tables; the term dependent on sin‘ 3 ¢ 
has always been taken into account if it exceeded 0”.05. The star- 
places were taken from the Nautical Almanac, and brsse1’s refraction 
was used. 
Below I shall first give as an example the detailed observations of 
one night, viz. February 25, 1911, at Mecca. 
The given temperatures and barometer-readings are corrected 
ones. The level-readings given are each time the mean of the 
readings before and after those of the verniers, which nearly always 
agreed fairly well iter se. They represent the deviations of the 
position of the bubble from the middle of the graduation, whereby 
the sign is taken positive when the reading of the bubble was too 
low and the reading of the verniers had to be increased. 
In the table the 4st and 2ed column contain the star and the 
position of the instrument; the 3°¢ column contains first the chrono- 
meter time of the pointing, then the hour angle derived from it; the 
Ah gives the readings of the two verniers, the 5‘ the employed 
zenithpoint. The remaining columns need no further explanation. 
Finally we have given the results for the latitude, such as follow 
from the observations of this night. 
