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 influefices several factors, these are readily de- 

 terminable. The primary effect of 

 slope is seen in the control of run- 

 ofif 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 1-90, 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. 

 This also necessitates the use of a 



Fig. 27. Mountain barometer: {a) in carry- 

 ing case; {b) set up for use. 



