74 THE HABITAT 
a ready clue to the relative amount of run-off in each fall of rain. The 
measurement of snowfall is often made merely by determining its depth. 
For comparison with rainfall, the rain gauge with receiver and tube with- 
drawn is used. The snow which falls is melted, poured into the measur- 
ing tube, and measured in the ordinary way. The U. S. Weather Bureau 
standard rain gauge, with measuring stick, may be obtained of H. J. Green, 
or of J. P. Friez for $5.25. 
107. Precipitation records. From the periodic character of precipitation, 
rainfall sums, means, and curves have little importance in the careful study 
of the habitat. The rainfall curve for the growing season is an aid in ex- 
plaining the curve of water-content, and the mean rainfall of a region gives 
some idea of its vegetation, though even here the matter of its distribution 
is of primary importance. The rain and snow charts published by the U. 
S. Weather Bureau furnish data of some importance for the general study 
of vegetation, but it is evident that they can play little part in a system 
which is founded upon the habitat. Precipitation records, for reasons of 
brevity and convenience, are united with wind records, and the form will 
be found under the discussion of this factor. 
WIND 
108. Value of read- 
ings. On account of its 
direct effect upon hu- 
midity, and its conse- 
quent influence upon 
water-content, the part 
which wind plays in a 
habitat can not be 
ignored in a thorough 
investigation. It is an 
important element in ex- 
posure, and accordingly 
has a marked mechani- 
cal effect upon the vege- 
tation of exposed habi- 
Fig. 23, Simple anemometer. tats, alpine slopes, sea- 
coasts, plains, etc. 
Owing to its inconstancy and its extreme variation in velocity, single wind 
readings are absolutely without value. When read in series, anemometers 
give some information upon the comparative air movement in different hab- 
