50 PHYSIOGRAPHY. [chap. 



hours is transferred from the collecting-can to the graduated 

 measure-glass, and its amount accurately recorded. 



Of the rain which falls in any given district, such as the 

 basin of the Thames, part is lost by evaporation and passes 

 invisibly into the air ; at the same time another part soaks 

 into the soil, and this also appears to be lost ; whilst part 

 again flows off the surface of the ground to lower levels. 

 Rain is thus disposed of in a threefold way, but the relative 

 proportion between the three parts will vary considerably 

 in different localities, and at different times in the same 

 locality. It is dependent on climate and season, on the 

 character of the soil, and on the physical features of the 

 district. But whatever the proportion may be, the rain 

 which is absorbed by the ground and that which flows off 

 the surface will contribute sooner or later to the formation 

 of springs and streams.^ And in this way the rains indirectly 

 nourish the rivers, since we have already seen that rivers 

 are mainly fed by spring and stream. The more rain which 

 falls upon the surface, the greater therefore will be the 

 yield of the river. " Rivers," said Captain Maury, " are the 

 rain-gauges of Nature." 



Atmospheric moisture is frequently condensed in other 

 forms than that of rain. If a glass of water recently 

 drawn from a cold spring be brought into a warm room, 



1 From what has been said respecting the origin of springs, it is 

 obvious that, independently of the effects of evaporation, the quantity 

 of water which readies a river may be less than that which falls in the 

 shape of rain upon its catchment basin ; inasmuch as some may go 

 to feed the springs of other catchment basins. And, on the other 

 hand, the quantity of water conveyed by a river may be indefinitely 

 greater than that which falls upon its catchment basin, if the geological 

 sti'ucture of the basin is such as to lead the rain from beyond its limits 

 into the /Springs of the river. 



