RESULTS OF COMPARATIVE OBSERVATIONS I BAVARIA. 239 



The dififerences at the several stations very nearly correspond when 

 the annual results of years are taken, although circumstances of soil 

 or exposure appear to have had a local influence in some cases. But of 

 these causes, none isj more apparent than that of elevation above sea- 

 level, the average becoming cooler as the elevation is greater.^ The ob- 

 served differences between stations are shown in the following table : 



Comparison of annual and summer temperatures of stations. 



It appears from the above table that the laws that govern the changes 

 of temperature in the soil are not much affected by differences of eleva- 

 tion. 



By inspection of the preceding table of temperatures by seasons, it 

 will be seen that while the deeper strata on the annual average are 

 colder than the upper ones, this difference is very slight in winter and 

 very considerable in summer. From this we may infer that the in- 

 fluence of latitude would be very sensibly felt, as the prevailing temper- 

 atures of hot and cold climates assimilate themselves to those of summer 

 and winter. Hence, woodlands afford much greater protection in sum- 

 mer than in winter, and the diffeiences should be more sensibly felt in 

 warm than in cold countries. The relative warmth of soil in winter in 

 the woods, as compared with open fields, may, perhaps, in part be 

 ascribed to its protection against cold winds, while in snowy countries 

 the detention of the snow in an even stratum must exert a notable in- 

 fluence upon the temperature of the soil by hindering the penetration of ' 

 frost. 



The cooler temperature of the deeper strata in spring may explain the 

 reason why trees that send their roots down deep into the soil, such as 

 the oak, do not put forth leaves as early as those where the roots lie 

 nearer the surface. 



The relatively colder soil of woodlands in summer has a close relation 

 to the retention of water and the maintenance of springs in wooded 

 regions, although hinderances to evaporation from the soil and its por- 

 ous condition in woodlands may be the principal reasons for the differ- 

 ences observed. 



On comparing the earth temperatures of spring and fall, we find at 



1 From observations made in the Siebengebirge, Bischof, of Bonn, calculated a de- 

 crease of warmtLi in the soil of 1° (R.) for every 6^3 Pari.s feet of elevation. From 

 observations made in Bavarian forests, a difference of 1° (R.) -was fonnd in 746 feet, 

 ■while between places of nearly the same level a disparity -was noticed that could not 

 be explained except iu inequality of soil and situation. 



