565 
Combining these 5 results with equal weights we should find 
+ 2™ 345.95 
which agrees with the final result adopted by us just within the 
limit of its mean error. 
7. Reduction of the results to known points in the two cities. 
Longitude of Mecca from the meridian of Greenwich. 
The situation of the observation-station at Jidda, (the Dutch consulate} 
relative to the Mecca-gate has been measured four times by 
Mr. Sarim by means of the determination of the direction and the 
length of the 4 parts of the road, the first by the boussole, the last 
by counting the steps, the length of which was found to be equal 
to 0™.768. To the directions counted from magnetic North to East 
first of all must be added, to reduce them into astronomical azimuths, 
the magnetic declination tor which, according to the English admiralty 
chart, —2°.4 was adopted. The thus corrected results, however, 
appear to be still in need of a correction of + 1°.6 *) according to the 
results obtained with the same instrument about the road from Jidda 
to Mecea, of which we shall treat hereafter. So the total correction 
of the lectures of the boussole was — 0°.8. 
From the directions and distances the rectangular co-ordinates have 
been derived taking as axes the parallel and the meridian. The mean 
results of the 4 measurements expressed in meters were as follows 
(see Plate II, tig. 1, the scale of which has been given in hectometers) : 
Ax Ay 
b—a — 94m + 350" 
c—b — 313 + 92 
d—-c 0 — 14 
e—d — 58 — 27 
Sum — 465™ +. 401™ 
The sums of the two first Av and Ay give as co-ordinates of the 
Medina-gate relative to the Mecca-gate 407" and + 442™, for 
which is found — 368™ and + 349™ according to the English ad- 
miralty-chart Jidda with its approaches. 1 adopted the mean of the 
two results and thus found as co-ordinates of the Dutch consulate 
relative to the Mecca-gate : 
1) The accurate result is + 27.0, but this difference is here immaterial. 
37* 
