530 
Fortunately the next year was in all respects more favourable 
for my enterprise. During my furlough in the summer OF 1O1O a 
again had the pleasure to work for three weeks at the observatory 
under the guidance of Prof. VAN DE SANDE BAKHUYZEN, and this time 
the heavens often gave an opportunity for observations. After my 
stay at Leyden I was moreover able to practise quite by myself 
for a few weeks in Gelderland with the instrument I had taken 
with me. 
Under good prospects I therefore returned to Jidda towards autumn, 
and when early in November the greatest heat and also the busiest 
time at the consulate were over, I could begin regular observations 
and also Mr. Sarm could practise systematically under my supervision. 
Soon we were able to execute determinations of time and of 
latitude alternately on succeeding days. But now we met with another 
mischance. The chronometer employed for the observations began to 
accelerate very much and very irregularly and at last it stopped 
altogether (December 2). Since no observations could be made with 
any of my pocket-ehronometers, the only thing left to do was to 
stop our observations until another box-chronometer could be for- 
warded from Leyden. 
Owing to this ill luek and on account of the irregular connexion 
between Holland and Jidda, a delay was caused of more than six 
weeks. Not till the end of January 1911 could we resume the obser- 
vations and with a view to the advanced time, it seemed best that 
they should further be done by Mr. Sarim alone. 
Thanks to his ability and zeal the series of observations undertaken 
could be brought to a satisfactory result between January 25 and 
March 23 1911. During this time three journeys were made to Mecca. 
Before the first journey and after the 1st, 2"¢ and 3" the corrections 
of the chronometers were determined at Jidda on 23 nights and 
during the journeys 14 determinations of time were accomplished 
at Mecca. Besides, the latitude of Mecca was determined on 10 
nights and that of Jidda on 13 nights, while for the last mentioned 
place already 7 determinations of latitude had been accomplished by 
the two of us in Nov.—Dec. 1910. 
Finally, a journey from Mecca to Jidda made on foot by Mr. SALIM 
with the determination of distances and directions enabled him to 
make a map of the road between the two places. 
As much as possible we calculated our observations ourselves, 
also to continually control our instruments, but of course the accurate 
calculation and the systematic derivation and discussion of the results 
could not take place until after my return to Holland.. These have 
