540 
Astronomy. — “Determination of the geographical latitude and 
longitude of Mecca and Jidda executed in 1910—11.” By 
Mr. N. Scnuurema. Part II. (Communicated by Prof. H. F. 
VAN DE SANDE BAKHUYZEN). 
(Communicated in the meeting of June 29, 1912). 
4. Determination of the geographical latitude of Jidda and Mecca. 
(Continued). 
About the results given in the two preceding tables it must still 
be noted that some of them in the first series at Jidda depend on 
one pointing only. These are: Nov. 23 North star T. R., Nov. 29 
North star T. L. and T. R. and Nov. 26 and Dec. 1 South star 
a sand ME: 
In the first place we shall now see what may be deduced about 
the accuracy of our observations as regards chance errors, from a 
comparison of the individual results. 
If the mean error of one pointing on a star be . . . .m 
a oe OF » Of one pointing on the signal be. . . . . M 
then we have 
. . . . 1 
m. error of the zenithpoint for the mean of the two threads a M 
(m. error)? of a zenithdistance derived from two pointings 
Dee 1 ih 
on the star in one position of the telescope . . .5m’ + 
We may now consider the m. error of a latitude p to be equal 
to that of the zenithdistance from which it has been deduced and 
thus we obtain: 
; 1 1 
(m. e.)? of p from one posit. = 1 = 3 m + ii M 
1 
OEP — aaa re 
1 
5 of Pr tg) rl 
i ee 
» Of ~(Py— Pg) = aig 0 
i en 
Ge erde — Ni gm 
from which: IL + Ul=1 
1 
T= WS = a. 
4 
