reaching Yen-an Fu were hurried—-owing to various circumstances— 
and the survey got in consequence considerably out, 16' of Long. and 
83' of Lat. It was adjusted by the distance as measured by road-wheel 
—incidentally showing to advantage this less ambitious apparatus—and 
a new base was established as described above in (B), from which the 
survey was begun afresh. 
At Lan-chou Fu, where I again joined the main body, the plane- 
table results checked out to 12' of Long. and 6' of Lat. 
The map, which is based on the plane-table sheets, has been 
adjusted to the correct positions of the various towns, as determined 
by observations. 
Latitudes. 
The Latitudes in the Table (on Page 170) are always the mean 
ot at least two observations, and more often of from four to six. As the 
greatest variation never exceeded 8”, we think they can be taken safely 
as correct. 
In taking the Latitudes for the ends of the base (B) the two 
theodolites were used, both Grant and myself reading 30 faces on each 
instrument. In one case the results checked to within 1°5” and in the 
other to 08". 
Longitudes. 
By the co-operation of Major H. R. Davies, General Staff, who 
kindly offered to take the Tientsin end, we were able to determine the 
telegraphic Longitude of T’ai-yiian Fu. One set of six taps at 10 second 
intervals, and another set of six at irregular intervals were sent and 
received on three nights. Four persons received at T’ai-yiian Fu, and 
two at Tientsin. The mean result was unexpectedly good, working out 
to a probable error of 4 seconds of arc. 
In taking the Longitudes by occultation at Yen-an Fu, Hsi-an Fu 
and Lan-chou Fu, never less than three observers took the time. The 
greatest variation between the times of two observers was three-quarters 
of a second. The immersions were always on the dark limb. These 
results can be taken safely to a quarter of a mile. . 
The Longitudes by Chronometer can, we think, be considered as 
exceptionally good. All but that of Fén-chou, Fu were between two points 
fixed by occultation or telegraph. Two separate Longitudes of Yii-lin 
Fu, one connected with the Longitude of T’ai-yiian Fu and the other 
with the Longitude of Yen-an Fu checked to 1’. 
a 
. 
132 
