534 
In Oct. 1909 11 determinations in 9 days gave 1 d. = 7.85 + 0".20 
in Oct. 1910—Mareh 1911 15 determinations 
in 42 Mays rie kT eS eee 
while all the determinations together would yield 1 d. = 8".46 + 0'.17 
Will it be better to use for our observations the value 8".91 or 
8.462 Since 8".7 had been actually used for the calculations, there 
did not seem to be any reason to change. The influence of an error 
in the value of a division on our final results is but small. A change 
in the adopted value by 0.5 would alter the results for the latitude 
of Mecca and of Jidda with less than 0".2. 
The zenithpoint was with a few exceptions determined every 
evening and each time for both the horizontal threads. In the following 
table have been collected the means of the two results together 
with their differences, i.e. the mutual distance of the threads. (See 
the table on p. 535). 
For each period there have been added the means of the daily 
results; in forming these means we have left out of account Nov. 
18 and 24, the results of which days are divergent. 
From this table it appears that in each period the zeiithpoints, 
determined on different evenings, mostly agree satisfactorily, but that 
after every journey the reading for the zenith has become a little 
higher. After the last journey back from Mecea it has considerably 
increased, with about 4.5, probably owing to a displacement of the 
level-tube with regard to the alidade. A few oscillations seem to 
appear in the thread-interval, white two very diverging results occur 
in Nov. 1910. 
4. Determination of the geographical latitude of Jidda 
and of Mecca. 
Coming to the observations proper [ will now first communicate 
the latitude determinations executed at Jidda and at Mecca and the 
results derived from these. For their reduction we must naturally 
know the corrections of the chronometer used, just as knowledge of 
the latitude is required for the reduction of the time determinations. 
I will, however leave the tables containing the chronometer-cor- 
rections till the next paragraph. 
With a few exceptions each latitude determination consists in the 
observation of a northern and of a southern star, each in the two 
positions of the instrument. Every time two pointings were made, 
one on each of the two threads; the level was always read before 
and after the reading of the verniers. 
