84 G. H. KNIBBS. 



siderable light upon the possibility of reaching merely approximate, 

 but sufficiently exact solutions for practical requirements in 

 characteristically similar areas or at least of interpreting meteoro- 

 logical records therein. Speaking generally, all hope of attaining 

 mathematical exactitude is quite Utopian. The complexity of 

 natural conditions is utterly beyond our mental grasp : the variety 

 of character, condition, and configuration of soils — on the state of 

 which vegetation is dependent — eludes all possibility of mathe- 

 matical expression. And besides this the effect of weather itself 

 in changing the character of soil in respect of the very thing we 

 propose to solve, viz., its degree of saturation, is wholly unsuscep- 

 tible of statistical definition. 1 The hope of attaining even a toler- 

 ably exact solution must therefore be regarded as illusory. The 

 exact solutions of ideal cases would however afford so valuable a 

 guide in an attempt to form numerical estimates of the resultants 

 of meteorological phenomena, and even in interpreting them, as to 

 fully justify their being undertaken. At the very least they will 

 afford either definite hope that we shall better understand those 

 physical conditions on which life and progress on this planet are 

 ultimately dependent, or else will compel us to realize the futility 

 of attempting to analyse conditions so complex as those which 

 here present themselves. Either would be gain : if one might 

 venture an opinion : the more hopeful view is the more probable. 



Finally it ought to be said that what may be called the biological 

 factors in the problem have not been yet adequately referred to. 

 As has been said vegetation itself is a source of exhaustion of 

 moisture on the one hand, and on the other it probably always 

 assists the saturation of the soil when rainfall occurs. In a satis- 

 factory solution its presence cannot be neglected, since it enters 

 with a large factor into the determination of the relation between 

 the amount absorbed and that lost. Human activity, in producing 

 conditions which promote absorption, is also a factor of moment 

 and cannot be ignored. Cultivated lands present distinct features 



1 For example : — The effect of frost in heating up the surface of a soil, 

 and the cracking of the surface during hot and dry weather. 



