v.] DRY SOILS ARE EARLY 135 



which there is always a gentle downdraught of cold 

 air from the clear sky above. But the circulation of 

 air in an anti-cyclone is always reversed at a certain 

 elevation, so that as one ascends, the downdraught of 

 cold air becomes less and eventually ceases ; the mean 

 temperature at the same time rises instead of falling 

 with the elevation. 



Observations of the minimum temperature on the 

 grass made at two stations on a gentle slope of the downs 

 at Wye, about a mile apart and differing in level by 

 100 feet, showed during a period of thirty-six days 

 in February and March 1902 (which was exceptionally 

 calm and mild), a mean difference of i° in favour of 

 the upper station, but on two occasions the lower 

 thermometer fell to 24°- 5 and 2i°-5, when the upper 

 thermometer was 30°* 5 and 29°- 5 respectively. 



The accompanying curves (Fig. 13) show the daily 

 maxima and minima of the air temperatures of 4 feet 

 from the ground for a few days before and after the 

 occurrence of a disastrous late spring frost in May 1902. 

 One station, A, was in a river meadow about 100 feet 

 above sea-level, the second, B, was on a terrace about 

 50 feet higher and half a mile away ; the third, C, was on 

 the flat summit of the down, 500 feet above sea-level 

 and about ij mile from the first station. It will be 

 seen that the river-side station gave always the highest 

 maxima during the period and the lowest minima, 

 showing on the one occasion n° of frost. 



Early and Late Soils. 



From all the considerations developed above it will 

 be seen that an early soil is essentially a coarse-textured 

 and well-drained one. Such a soil retains little water, 

 thus possessing a low specific heat, and is easily warmed ; 



