THE SCIENCE OP FRONTIER DELIMITATION, 
219 
latitude of that place must be known or it must be fixed. The obser¬ 
vations must be carefully made, by taking circummeridians of a pair 
of stars. As it is possible that different results may be obtained by 
the two commissions, and as it is not likely that the latitude can be 
found within 200 or 300 yards, since the instruments read to 10", 
i.e., to about 337 yards, that amount of error may be expected, taking 
into consideration the difficulty of getting the refraction exact, and 
allowing for personal errors, the simplest course is for the two com¬ 
missions to meet, for each to observe, both parties taking down the 
angles as observed, noting the times with their own watches and 
computing the results independently. From the mean of two or three 
such observations, provided they are reasonably concordant, a good 
value for the latitude should be obtained and the commissioners should 
be able to agree on the position of the starting point. For survey 
purposes, though not for delimitation, the longitude of this point should 
also be obtained. 
When the starting point is fixed, an observation for true bearing 
must be made from it. The best time for this is at sunset, when it is 
possible to see through the telescope both a star and some distant 
object to serve as a referring point. In a country like West Africa it 
is rarely possible to do this, and day observations must be made, or 
night observations with a lamp on some point as a referring mark. 
If the line is to be run with a theodolite, the usual course is to set 
up the instrument at the starting point, to lay off the required angle 
from the referring object so as to bring the telescope into a true east 
and west line, and to send a man to the most distant elevated point 
visible in this line, moving him by signal to right and left till his flag 
rests on the intersection of the cross wires. The instrument is then 
moved to this flag, set up there and laid on the starting point and the 
telescope turned 180° in azimuth, not reversed in altitude, for that 
brings in the error of collimation, and a second flag is fixed in the 
same way as the first. The vernier plate must be brought round 
again till the cross wires intersect on the starting point, and the 
horizontal verniers should be read, to see if there is any deviation 
from 360°. The defect of running a line in this way is that an error, 
which may easily occur from any slight displacement of a flag, in¬ 
creases as the line is delimited. To avoid this, the bearing should be 
carefully taken at each station. A simple and sufficiently accurate 
method of running a parallel is by using an instrument like the French 
boussolle Brosse , a theodolite compass, consisting of a large compass 
in a horizontal position, which, by means of a key, can be set so that 
the readings taken through the telescope are true bearings. The 
compass is adjusted in a true east and west line, and it is then not 
necessary to take any forward bearing as long as the back station is 
visible. The instrument is taken as far to the front as possible so that 
the back station is visible, and is then moved north or south till it is 
in a true east and west line with this station. Observations for 
latitude and time must be taken occasionally in order to check the 
azimuth line and to carry the meridian distance. The closing point 
