PHYSIOGRAPHY 83 
Slope 
121. Concept. This term is used in the ordinary sense to indicate the 
relation of the surface of a habitat to the horizon. Although it is a com- 
plex of factors, or rather influences several factors, these are readily de- 
terminable. The primary effect of 
slope is seen in the control of run- 
off and drainage, and consequently 
of water-content, although these 
are likewise affected by soil tex- 
ture and by surface. Slope, more- 
over, as a concomitant of exposure, 
has an important bearing upon 
light and heat by virtue: of deter- 
mining the angle of incidence, and 
also upon wind, and, through it, 
upon the distribution of snow. At 
present, while it can be expressed 
- definitely in degrees, it has not yet 
been connected quantitatively with 
more direct factors. This is, how+ 
ever, not a difficult ‘task, and it is 
probable that we shall soon come 
to express slope principally in 
amount of run-off, and of incident 
heat. 
122. The clinometer. In the 
simplest form, this instrument is 
merely a semicircle of paper, with 
each half graduated from 1-go”. It 
is mounted on a board and placed 
base upward, upon a wooden strip, 
2 feet long and 2 inches wide, 
which has a true edge. At the cen- 
ter of the circle is attached a line 
and plummet for reading the per- 
pendicular. A more convenient 
form is shown in figure 28, which 
is both clinometer and compass. Fig. 27. 
. : : : Mountain barometer: (@) in carry- 
This also necessitates the use of a ing case; (5) set up for use. 
