126 A MANUAL FOR NORTHERN WOODSMEN 
tops by intersection may suffice for topographical purposes, 
while it gives a juster view of the timber than could other¬ 
wise be gained. Locations, too, will be more accurate 
along such a line than where a crooked route is followed. 
4. Extreme points are in general the ones to read on 
for height, — that is to say, ridge tops, brook crossings, etc. 
One may combine with this also a system of reading at 
regular intervals. It will be enough to read the thermom¬ 
eter half a dozen times during a day to get the course of 
the temperature, unless extremely high points are occupied. 
5. Relative heights are frequently of far more importance 
for logging purposes, as, for instance, in connection with the 
grade of roads, than is absolute elevation. It is often ad¬ 
visable, therefore, to establish sub-centers of work and 
determine elevations relatively around them rather than 
refer readings always to a distant base station. On the 
same principle, if a region is hard to get at with the level, it 
may serve the purpose of the map to fix the height of some 
central point in it by two or more aneroid readings, and 
then work around that. 
