529 
interested in my planus and kindly promised me help and advice. 
The execution of the work was now rendered possible and by the 
kind dispensation of His Excellency the Minister of Foreign Affairs, 
to whom I here respectfully render thanks, I received a royal 
commission to execute astronomical observations in the Hedjaz. 
Let me say first of all in what way I intended to set about the 
proposed plan. As it was quite impossible for me to enter Mecea 
and make observations, the help would be asked of Mr. A. Sati, 
Pupil-Secretary-Interpreter of the consulate. Asa Mohammedan be was 
perfectly free in his movements within the holy domain and having 
finished the 5 years’ course of the Secondary School at Batavia, he 
was sufficiently well-grounded to successfully make the astronomical 
observations. Let me add that Mr. Sarim showed an eager interest, 
when I communicated my plans to him. 
According to the consultations with Prof. BAKHUYZEN a more detailed 
plan was now made out for the execution of the observations. For 
the determination of the latitude of Mecca circummeridian-altitudes 
of stars were to be observed and the same was to be done also at 
Jidda, partly for practice, partly for the examination of the instru- 
ment and of the employed method of observation and finally to 
mutually control the results obtained by the English bydrographers 
and by ourselves. Secondly the difference of longitude between Jidda 
and Mecca was to be determined by transporting some chronometers 
to and fro between the two places, if possible a couple of times, 
while during the stay in each place as many determinations of time 
as possible would be made by altitudes of stars in the east and in 
the west. All the observations at Mecca having to be accomplished 
by Mr. Sati, also the corresponding determinations of time at Jidda 
wanted for the derivation of the difference of longitude were to be 
executed by him. All the observations were to be made with a small 
altazimuth. 
First of all I now tried to use the rest of my furlough to practise 
making observations at the Leyden observatory. The exceedingly 
unfavourable summer of 1909 gave, however, only very rare oppor- 
tunities for observations and so I had to leave again for Jidda at 
the end of July without having acquired sufficient skill in observing. 
Consequently the observations [ accomplished after my arrival at 
Jidda left much to be wished for in arrangement as well as in 
accuracy. Besides, other circumstances, among which an extremely 
busy time at the consulate, concurred in impeding the work. Owing 
to all this the material collected in the winter of 1909—10 has so 
little value that we can henceforth leave it out of account. 
35 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
