LX. R. T. McKAY. 
sents the mean rainfall over the whole catchment. This 
method gives more accurate results than that frequently 
used of taking the mean of all the records within the total 
area. The following shews the formula adopted in arriving 
pete we Spl liesren 
V.vV.V:;etc. = Volumes of rainfall over each partial area 
in cubic inches: 
R, R. R,z etc. = Rainfall in inches over each partial area. 
A, A» Ag etc. = Area in square milesover each partial area. 
A,, = Area in square miles of whole catchment. 
C = 640 x 43560 x 144 = Co-efficient to reduce to sq. in. 
D = Depth in inches of rainfall over whole catchment, then 
Wa | 7 Ty e | t [a 1 
Vy. see Yaa. ‘ye OVA + OAs R2+CA;R; ah. 
oad CA, 
Na R, A> R 2 As Rs 1h 
— ah, ir See | 
A W | A Ww - A Ww 
The above formula resolves itself into ascertaining the 
proportion that each partial area bears to the whole area, 
and using that proportion as a co-efficient to apply to the 
mean of ail the rainfall records of the observing stations, 
Within each partial area. Thirty-five observing stations 
were used to determine the mean rainfall, the highest 
station being at Kiandra with an altitude of 4,640 feet, 
next in altitude being Nimitybelle, 3,465 feet; Adaminaby, 
3,000 feet; Cooma, 2,660 feet; the other stations gradually 
decreasing in elevation as we go northerly to Gilgal, about 
1,200 feet in height. The area of maximum rainfall sur- 
rounds Kiandra, which conforms to the accepted theory 
that rainfall increases with altitude, but the rule is not 
borne out when we compare Cooma with its elevation of 
2,660 feet and Tumut 900 feet, as the following table will 
show. A peculiar belt of low precipitation surrounds Cooma 
on the Monaro Plains. It is situated in what might be 
termed a horse-shoe bend, with mountain ranges to the 
west, south, and east, which intercept the clouds and rob 
