2 Scientific Proceedings, Royal Dublin Society. 
much attention, because the saturated earth evaporates rapidly. 
What the unobservant observer seems not to notice is that 
irrigated land dries up even more quickly in dry weather than 
land wetted by rain. In any case, the rate of drying depends to a 
great extent upon the nature of the soil: sand, e.g., drying much 
more quickly than clay. The following is a case in point :—Some 
months ago I made a series of comparative observations upon the 
ordinary poor red sand of the South African veldt and the blue 
clay of the Kimberley diamond mines, noting the behaviour of 
each with respect to the absorption and radiation of heat, and the 
absorption and evaporation of water. A rough measurement gave 
the relative specific gravity of the sand to the clay as about 18: 14, 
and the latter showed a much smaller range of temperature than 
the former, when the two were exposed side by side in the open 
air. Also water percolated much more freely into the sand than 
into the clay. In the experiment that bears directly upon this 
discussion I took equal weights of sand and clay, dried them, 
crushed them up as fine as possible, packed them tightly into 
nearly identical silver-plated cups, and then saturated them as 
nearly as possible with equal weights of water, the total weight 
of earth and water being finally 4728 grains. They were then. 
placed side by side in the shade,’ with the object of keeping 
them at nearly the same temperature. The following were the 
synchronous losses by evaporation until they attained a sort of 
hygroscopic balance with the air. 
Tasie 23.—Comparative Losses by Evaporation. 
Blue Clay Red Sand 
First to Third day, : 4 | 90 grains 109 grains 
Third », Fifth day, F 2 | 4D. gy EN As 
Fifth », Seventh day, . ua 58) be CGN Al 
Seventh », Tenth day, 5 ba SOMES 24s, 
Tenth », Twelfth day, . : 29) Te. 19 ,, 
Twelfth », Fifteenth day, . : 2 a So 96 
Fifteenth ,, Twenty-second day, . | Os ie WO 55 
Twenty-second ,, Twenty-eighth day, . | = 8. 5p mass) 5 
1 In the shade of a louvered screen. 
