Failure of the Yan Yean Reservoir. 145 
TasBie I1I.—Showing the Mean Rain and the amount of Rain 
evaporated, and the Watershed, or that portion of the Rain 
that escapes evaporation in Victoria, deduced from Mr. Demp- 
sey’s Tables :— 
MEAN RAIN. EVAPORATION. WATERSHED. 
January . 1°36 1°34 0:02 
February . 0°95 0°93 0:02 
March . . 1°60 1:57 0:03 
April . . 3813 3-07 0:06 
eS Maye at StOe 3°45 0:22 
June . . 2°41 1:90 051 
lye 2102 er 2:18 171 0°47 
August. . + 3°61 2°85 0-76 
September . 3°27 3°08 0-19 
October . 2°54 2°36 0:18 
November. 427 4:21 0:06 
December. 1°86 1°83 0:03 
Total 30°85 28°30 2°51 
In illustration of this method I shall take our month of 
January, which has a mean temperature of 67° 94. On re- 
ferring to Mr. Dempsey’s tables I find that August in Eng- 
land has a mean temperature of 61° 6. Now, what can be 
more just or more in accordance with scientific accuracy, 
than to conclude that the proportion of the rain evaporated 
in our January is at least as great as that in the August of 
England ? 
In the same way I shall take our July, which has a mean 
temperature of 49° 34, and I find that April in England has 
a mean temperature of 49° 9. Am I not then warranted 
on scientific grounds to assume that the proportion of the 
rain evaporated here in July is equal to that of April in 
England? Now it is precisely in this way that I have de- 
duced from Mr. Dempsey’s tables that 2°51 inches, or one- 
twelfth of the rainfall adopted by the Committee, represents 
the proportion that reaches the Plenty. 
I do not insist that Mr. Dempsey’s tables are correct; but 
if they are so, then it would appear that the watershed of 
the Plenty is much less than I made it. His tables give 
2°51 inches; I estimated 4°50 inches as the nearest approxi- 
mation, and there is a vast difference between 2°51 inches 
and 10°69 inches when multiplied by sixty square miles of 
surface; and this is the watershed adopted by your Com- 
mittee for eight months of the year. And as every point is 
Q 
