194 Report of the Commissioners on the 
as in still water, to obtain the loss from which, the annual 
depth evaporated should be multiplied into the superficial ex- 
tent. We have been kindly favoured by Dr. Davey with the 
results of his experiments on evaporation in still water, for 
the three summer months, which give °55 inch per day, equal 
to 42°5 inches for the three months. He has further furnished 
us with a proportionate evaporation for the rest of the year, 
as follows :— 
Evaporation for the six autumnal months, equal \ UY 
to four-thirds of the three summer months °° ae 
Evaporation for the three winter months, equal) 9.5 ; 
to one-sixth of the three summer months, equal $ 2s: 
And adding evaporation for the three cua 49-5 aneheR 
months con ae and ac Boe 
We have ta aa in ae aa 123°7 inches 
or 10°3 feet equal depth of water evaporated annually. 
As this amount was partly derived from inference and 
therefore not absolutely proved, however certain; we re- 
quested Dr. Davey to furnish us with such an amount as in 
his opinion did not admit of a doubt, and were accordingly 
informed that we might safely adopt nine feet. 
Hence the amount evaporated in the western swamp can 
be obtained by multiplying the superficial extent, equal to 
787,000 square yards by the depth of evaporation, or nine feet, 
but as 17°856 inches has already been allowed for surface 
evaporation over the whole basin, this amount must be de- 
ducted from the nine feet, thus leaving 7°512 to be multi- 
plied into the area of the swamp, thus giving 1,970,648 cubic ~ 
yards evaporated per annum on the western swamp. 
The loss by evaporation in the swamp on the eastern arm, 
must be determined in a different manner, inasmuch as the 
water is not spread over its surface, but rather absorbed by it. 
This loss is accurately represented by the difference between 
the measured discharge above and below the swamp on the 
same day; the discharge of the eastern arm, near the head of 
the swamp, was on January 24th, 37,990 cubic yards per day, 
the sectional area being fourteen square feet, and mean 
velocity 10.18 inches per second; the discharge below the 
swamp, at junction of the Plenty with aqueduct, was 21,653 
cubic yards per day, the sectional area being 13-2 square feet, 
and mean velocity 6°15 inches per second; the discharge 
