COMPASS SURVEY. 
81 
direction of the route. In a country thickly covered with forest it is 
most difficult to distinguish landmarks. The traveller may, however, 
sometimes leave a mark recognisable at some miles distance by giving 
a little consideration to it, and knowing the direction in which he is 
proceeding. 
Enter every observation and change made in the general direction 
travelled, with the date and time, in the journal; as without attention 
to this, much valuable information may be lost. When preparing MS. 
to be sent home for publication, write each of the native names, at least 
once , in printing character. Numerous errors and great loss of time 
frequently result from the attempt to decipher proper names written by 
travellers in their ordinary handwriting only. 
As has been stated, p. 80, the weak points in route surveying with 
prismatic compass are the errors caused by false estimates of the distance 
travelled, and those arising from the effects of local attraction on the 
compass. It is by no means easy to guard against these erro:s creeping 
in, and false estimates of distance are * frequently brought about by the 
different nature of the surface of the country travelled over, as, for 
instance, when there is a change from firm open country to jungle or 
heavy sand, as the times occupied to traverse the same distance under 
these changed circumstances will differ considerably, and a time scale 
prepared for one will be useless for the other. 
It is here that sextant observations become so valuable for correcting 
errors arising from the above sources, and even if a traveller has only a 
sufficient knowledge of its use to take the latitude, it will go far to 
increase the accuracy of his map, as the following diagram will 
show (p. 82). 
Suppose a person to travel from A to B in the direction A B, and 
that his estimated distance, by the scale of his map, places him at B 
in latitude 22° N., but when he observes the meridian altitude of a star 
he finds that his latitude is really 21° 55' N., and that he has over¬ 
estimated his distance travelled by the distance C B, and that he really 
is at C and not at B. If this observation had not been taken he would 
have made B the point on his map to commence plotting his next day’s 
journey, which would have led to considerable errors not only in his 
latitude and longitude, but also in the positions of the different points 
he fixed along his route, but by taking C as his starting point he not 
VOL. I. G 
