130 A MANUAL FOR NORTHERN WOODSMEN 
denied, however, that rapid weather changes sometimes 
make accurate work difficult. 
Some interior mountain territory is characterized by 
lightly forested ridges contrasting with great density of 
timber and brush along the streams, while logging methods 
are often such that accurate knowledge of grades on valley 
lines is not essential. In circumstances such as these, 
circuits of transit and stadia work carried over the ridges 
have proved a satisfactory method of height control. 
When areas concerned have never been covered by the land 
surveys, angles have been turned and read in addition for 
the purpose of control in the horizontal direction. 
With control laid out in this way the early plans of 
reconnaissance in such country involved, as the next step, 
the crossing of valleys with strip surveys, the aneroid 
being relied on for elevation. This plan of work, starting 
from known points on the ridges and running long lines 
independent of one another, crossing the brooks and valley 
bottoms (where grade was most important) at a long 
distance from known bases both horizontally and verti¬ 
cally, made demands on the aneroid which it was not able 
to meet successfully. 
Height work along the stream lines was an evident 
corrective, but a substitute scheme that at the time of 
writing seems to be filling the requirement is the use of the 
tape and clinometer. 1 Both instruments have, however, 
been subjected to modification. The clinometer has been 
made more efficient in numerous ways; in particular the 
arc has been enlarged and so graduated that instead of 
degree or per cent of slope it gives difference of elevation in 
feet for the given slope and a stated distance (66 feet or one 
chain in present practice). The tape used for the purpose 
is 2 \ chains long, two chains of it marked in links as usual, 
while the extra length or “trailer” is so graduated that 
the inclined distance along any slope which corresponds to 
two chains horizontal may be set directly. By these 
devices two short cuts are accomplished: first, difference in 
1 For a fuller description of this method see “The Timberman,” 
March, 1916, or “Engineering News,” Vol. 75, No. 1 , p. 24. 
