Minutes of Proceedings. xvii 



observed at Kenilworth (Kimberley) during the ten years 1897 to 

 1906, for depths ranging from the surface down to six feet. The 

 daily maximum temperature of the surface of the ground, like the 

 maximum temperatures in the sun and shade, depends upon 

 the meridian altitude of the sun, i.e., the ground is warmest by day 

 at midsummer and coldest by day at midwinter. But the annual 

 maximum and minimum lag as the depth increases, so that at a 

 depth of six feet the ground is warmest about the beginning of 

 March and coldest about the middle of August. The ground seems 

 to have been generally warmer during the first five years than it was 

 during the second five of the period discussed. As it happens, there 

 was a similar variation in the sun and air temperatures both at 

 Kimberley and Durban. Some interesting results are obtained from 

 the harmonic analysis of the various annual curves of temperature, 

 but the diffusivity for shallow depths computed from the harmonic 

 constants is not very satisfactory. The disturbance of earth tem- 

 perature initiated by rain penetrates downwards at the rate of about 

 ten inches a day. The annual cold spell of the middle of July is 

 felt at a depth of at least two feet. 



