547 
from which follows AZ—= + 1".0, i.e. the same value as was found 
from the determinations of latitude 
Secondly the results from the eastern and the western star have 
been compared inter se and the mean values obtained were: 
Jidda 23 nights K—W = + 05.13 
Mecca 13 5 +0 .08 
Together 36 7 E—W —= + 08.11 
If this difference is produced by a constant error in the measured 
zenithdistances, then we find for its amount Az = + 0".8, while 
+1".7 had been found from the determinations of latitude in 
which the average zenithdistance was somewhat smaller. From a 
comparison of the separate values for E.—W. with their general mean 
we find, however, as mean error of the difference found in a single 
night + 08.68, hence of the result from 36 nights + 05.10, which is 
equal to the mean difference itself. The obtained results are, howe- 
ver, satisfactory, as we may conclude that no great unknown sources 
of error have been at work. 
Disregarding a possible systematic personal error, we may further 
consider the mean error of }(E-++-W) as equal to that of 4 (E—W), 
and we thus obtain as mean error of a chronometer-correction from 
an eastern and a western star + 05.32, 
At each time-determination the Leroy watches were compared 
with Dent. In the meantime Leroy 5180 = Dutch navy 3 had 
stopped and on the journeys to Mecca only 2 or 3 watches were 
taken (2 on the first and second journeys, 3 on the third) for fear of 
a possible mishap. Prudence demanded this, although now that 
everything went off well, I regret that all the watches were not 
taken each time. Naturally the mean errors of the observed correc- 
tions of the watches will be somewhat greater than in the case of 
Dent, owing to the errors of comparison. 
The following tables contain the observed corrections for Dent and 
the Leroy-watches and the thence derived daily rates; the first two 
tables according to the observations at Jidda, the next two according 
to those at Mecca. On Febr. 25 Leroy 4129 = Dutch navy 77 was wound 
up too late after it had already stopped (see the tables on p. 548—550). 
It is clearly visible from the daily rates contained in the preceding 
tables that the time-determination of Febr. 26 at Mecca, based on 
one star only, has been less accurate. The same appears with even 
greater force for the one of Febr. 21 at Jidda, although the ob- 
servations of that night are apparently irreproachable. 
For a closer investigation of the regularity of the watches we 
shall use the rates which have been obtained during the stay at 
36* 
