76 
HINTS TO TRAVELLERS, 
The scale of the intended survey is an important point. 
This will vary ranch with circumstances, but the limits of scale for 
ordinary route surveys may be roughly stated as from half an inch to 
one-tenth of an inch to the geographical mile. 
The geographical mile should be chosen, as it facilitates the intro¬ 
duction of astronomical positions from time to time. 
While parts which seem to require more detail may be mapped on a 
larger scale, and reduced into the general map, it will ordinarily be 
found that a scale of five geographical miles to an inch will be the most 
convenient. 
It is above all things necessary that a traveller should state distinctly 
how his map has been made, the bases used, the instruments employed, 
and generally all information that will enable the map compiler to judge 
of the value of the work. The compiler has in most cases to fit the new 
work into old, and without some information which enables him to 
appraise the value of both, he is at a loss what to do when dis¬ 
crepancies, which are unavoidable in such work, occur. 
Some portions of a route map are certain to be less accurate than 
others, and the traveller should append remarks on this head, because 
the object of all travellers surveying is to add to correct mapping, and 
not to displace previous work by the new, without regard to the accuracy 
which may attach to it. 
Any work incorporated from a previous map should be distinguished 
in some way to avoid confusion, and if such work has been altered to fit 
the explorer’s positions, it should be stated. 
Route Survey with Prismatic Compass , Boiling-point Thermometer , 
and Aneroid. 
For the purpose of illustration, suppose the following to be an extract 
from a traveller’s journal 
June 1st. —Camp at the foot of hill A,’ and 2f miles distant from its 
summit, the magnetic bearing of which was 146°. 
To measure the height of the hill A, above the camp, I read the 
aneroid and thermometer, first at camp and then on its summit, with 
the following resultsAt camp, aueroid, 25*67 inches; temperature in 
