57 
necessary to accomplish this, and that, too, to a greater degree if the 
soil be covered with vegetation. The phenomena ‘of autumn generally 
resemble closely those of summer. 
(23) In general the fluctuations in the temperature of the earth 
are not less “dependent on the precipitation than on the variations in 
the temperature of the air. 
SOIL TEMPERATURES AS AFFECTED BY SURFACE SLOPE AND 
COVERING (WOLLNY). 
In reference to the effect of the slope of the earth’s surface on the 
temperature of the soil, Wollny (1888, p. 364) has made an extensive 
series of measurements at Munich from which he draws the following 
conclusions in continuation of those published by him in 1883. His 
temperatures were measured bihourly at a depth of 15 centimeters 
under both fallow soil and grass sod; the differences referred to 
amounted to 3° and 4° F. in individual cases, but on the average to 
searcely 1° F’. 
(1) That soil whose exposure is toward the south is the warmest, 
then comes the east, then the west, and finally the north exposure. 
(2) The southern exposure is warmer in proportion as the inclina- 
tion to the horizon is greater. 
(3) The difference of temperature between the north and south 
exposure is much greater than between east and west. 
(4) The difference in the warming of the soil for north and south 
exposures is greater in proportion as the surfaces have a greater 
inchnation. 
Wollny (1888, p. 415) has also investigated the influence of the 
covering of straw and chaff on the temperature and moisture of the 
soil. He finds the following conclusions: 
(1) That at a depth of 10 centimeters the naked soil is warmed 
more with rising air temperatures and is cooled more with falling 
air temperatures than, under any one of the different forms of straw 
covering. 
(2) That the variations in the temperature within the straw litter 
are very much less than in the earth. 
(3) That the earth is in general somewhat colder than the material 
of which the htter is made, except when the latter is moss. 
(4) That among the various materials forming a litter the pine 
needles are warmed the most, the oak leaves and the fir-tree needles 
are less warm, while the litter of moss is the coldest. 
The different temperatures observed were as follows, on the average 
of the months April to September: Pine needles, 16.93° C.; oak leaves, 
16.62° C.; fir needles, 16.34° C.; the naked soil at a depth of 10 
centimeters, 16.18° C.; moss, 15.95° C. 
