161 
sun, upon a very interesting occasion, because the 
former was in the west, whereas during all my former 
observations at Djedda, she had been constantly in the 
east. 
During the whole of my stay at Mecca, there was but 
one eclipse of the first satellite of Jupiter. It took place 
on the morning of the 22d of February. I ascended a 
neighbouring mountain to be the better able to observe 
it, for the phenomenon took place shortly after the rising 
of the planet; but another mountain higher than the one 
upon which I stood, hid the star from me until after 
the eclipse had taken place. In consequence of this oc- 
currence, my longitude of Mecca is determined only 
by lunar distances, the result of a great number of ob- 
servations taken right and left. 
I observed at Djedda on the 17th of March an emer- 
sion of the fourth satellite, and an immersion of the first. 
These fortunate observations combined with those of 
the lunar distances taken the first time, gave the longi-' 
tude of Djedda, which is 36° 45' 45" east from the 
observatory of Paris. A number of passages, verified 
and combined with my preceding observations, have 
determined the latitude of Djedda to be 21° 32' 42" 
north. Several solar azimuths, added to those I had 
previously taken, make the definitive magneticai de- 
clination 10° 8' 18" west. 
The magneticai declination at Mokha is reputed to 
be 8° 30', and at the Straits of Babelmandel nearly 7°. 
I ascertained that it was 13° 30" at Suez, so that it 
diminishes constantly along the Red Sea in the direct 
tion of the south-east. 
There is seldom any rain in these countries sur- 
rounded by sandy deserts, except during the autumnal 
Vol. II X 
