CXVI. DISCUSSION. 
With all due respect to the Professor, I may be permitted 
to say that, he appears to have entirely failed to grasp the 
importance of the water table, or level of the saturated 
zone in the soil, which varies greatly in depth below the 
ground surface, and governs the flow of streams in the 
absence of rain, and taken in conjunction with the amount 
of evaporation, degree of porosity of the soil, and the slope 
of the ground surface, controls the surface “‘run off.”” As 
the water table is affected directly by the excess or 
deficiency of rain, the only way by which to determine the 
exact position of the water table, is of course, by ascer- 
taining its level in tubes or wells sunk in suitable places. 
In the absence of these measurements there is no other 
way of approximately estimating the rise or fall of the 
water table, than by ascertaining the accumulated rise or 
fall of rain above or below the mean over a long term of 
years. The residual mass curve shows in the best possible 
way the cumulative effect of the rainfall in excess or 
deficiency in relation to the mean. 
The Professor says that this method is new to him, and 
because the curve as derived from the rainfall at one place, 
does not agree with another, or that a drought is shown in 
a high part of the curve, following abundant rainfall a few 
years previously, he objects to the method. He does not 
seem to realise that, each place is a “law unto itself.” 
The comparison of the curves constructed from the rainfall 
returns at all the long record stations in Australasia, show 
clearly that each place has its own peculiar periods, accord- 
ing to its elevation above the sea level, and its geographical 
position, especially with reference to the distance from the 
coast, and proximity to the mountain range. If he will 
construct a residual mass curve from the Hobart record, 
and compare it with the Melbourne one, he will find that 
the periods are exactly the reverse of Melbourne. If 
