DISCUSSION. 73 



moisture does not fall to the ground and is removed by 

 evaporation. 



Mr Mann : — On the Illawarra the decomposed leaves are 

 never dry. There could never be a fair test. 



Mr. Russell : — It is usual in taking observations to determine 

 the rainfall in forests, to place one rain guage on the ground in 

 the open near the forest, and another in the forest in a place 

 where the trees are cleared away, the reason, no doubt, why an 

 elevated rain guage catches less rain than one on the ground is 

 that the velocity of the wind is greater as you rise from the 

 surface of the ground, and the mouth of the guage produces a 

 little vortex motion of the wind which throws the rain out. 

 The question has never been thoroughly investigated as to what 

 effect, if any, forests have upon the rainfall, in fact it would 

 require a great many years of observation before the question 

 could be settled. 



Mr. W. M. Hamlet : — I quite agree with Mr. Russell, that we 

 have no scientific data to enable us to determine the effect of the 

 rainfall in connection with forests. It appears to me one thing 

 has been lost sight of in connection with this discussion, and that 

 is the natural function of the leaf of a tree, namely, that of 

 evaporation ; and my own idea is that we may account for the 

 occurrence of these springs after ring-barking in this way. Let 

 us take the total area of all the leaves of a tree or a number of 

 trees, and compare that with the area of the ground upon which 

 the tree stands, the total area obviously will be considerably 

 greater. Now, during a tree's life evaporation is going on, and 

 water is being drawn up from the soil in order to produce the 

 effect of growth in the tree. After ring-barking evaporation 

 ceases, and there being no longer any outlet for the water from 

 the soil, it must necessarily follow that the water which is already 

 in the soil, and which has been accumulating in consequence of 

 repeated rains, must find an outlet. That, I think, will account 

 for the boggy nature of the soil after ring-barking under the 

 conditions stated by Mr. Mann. Then, with regard to the 

 remarks made by the gentleman who opened this discussion 

 to-night. He said that there was a difference of atmospheric 

 pressure on forest land — that there was a greater amount of 

 pressure on forest land than on cleared land. I think that is 

 utterly erroneous. I think if we took a barometer and stood it 

 in a forest, and then took it to cleared land in the vicinity, there 

 would be absolutely no difference whatever with regard to 

 pressure, and that the diminution of pressure in any one place 

 would not account for this previously dry place becoming covered 

 with streams of water. I think the true explanation would lie in 

 the question of evaporation. 



