58 
The difference between the morning and evening temperatures 
shows: 
(1) That the cooling during the night and the warming during 
the day is appreciably larger for the naked earth than for the various 
kinds of litter. 
(2) That the pine needles warm up most during the day and the 
moss warms up least; that the fir needles cool most during the night 
and the pine needles least. 
The power of retaining moisture varies with the different kinds of 
litter as follows: 
(1) Any litter of forest leaves or needles is moister than the earth, 
but the moss is less moist than the earth; the gradation is from oak 
leaves, the highest, through fir needles to moss, the lowest. 
With regard to evaporation Wollny shows that the naked earth 
loses a greater quantity of moisture by evaporation than do the 
various kinds of litter. 
(2) That the moss litter evaporates the most, but the litter of forest 
leaves the least. 
(3) That the quantity of evaporation is greater the thinner the 
layer of the litter. 
In general, then, the litters of leaves and of pine needles give up 
the rain water that falls upon them to the ground beneath in larger 
proportion, but still continue to be very moist because they lose, rela- 
tively, little water by evaporation; furthermore, that the moss litter 
is distinguished by large variations in its contained water because 
it has on the one hand a large capacity for water and on the other 
hand a very considerable evaporating power. 
SOIL TEMPERATURES OBSERVED AT GREENWICH, ENGLAND. 
Among the limited number of long-continued series of observations 
of temperatures of soil near the surface is that maintained at Green- 
wich Observatory, England, since June, 1846.° This series embraces 
observations at considerable depths that will not interest the student 
of agriculture, but we reproduce in the following table the results of 
observations at 1 inch in depth, as given in the annual volumes of the 
Greenwich Observatory for 1878, and as given in J. D. Everett’s 
memoir of 1860. These soil temperatures can be used in any sub- 
sequent study of English crops throughout the southern half of 
England or in analogous climates. 
