RESULTS OF COMPARATIVE OBSERVATIONS : SWITZERLAND. 259 



lY.— Difference of mean temperature of tlie soil in the woods above or beloiv that at similar 

 depths in the opien fields. (Centigrade). 



Upon comparing? the numbers in this table it will be seen, that in the 

 winter months the soil of the open fields is almost invariably colder than 

 in the woods; but that in summer, the difference is very considerably 

 changed, the soil of the woods at all depths, and with all kinds of tim- 

 bers observed, being much cooler than that in the fields. The difference 

 at the first and third stations was much greater at the surface, and dimin- 

 ished with the depth. This range of difference is almost invariably 

 greatest in August, and it disappears very rapidly in the autumnal 

 months. As in the case of the temperatures of the open air, the differ- 

 ence increases and diminishes more regularly with the beech than with 

 either the larch or the fir. In all cases, with but a single exception, the 

 difference increases steadily to its maximum, and then again declines. 

 The exceptional instance is that of the surface temperature at the Berne 

 station, where the mean of eight years gives a difference of 4.27 in April, 

 4.05 in May, and 4.56 in June. 



