622 Proceedings of Royal Society of Edinburgh. [sess. 
The net result of the gaugings shows that the average annual 
rainfall on the drainage area during the period of seven years was 
62*51 inches. 
Of course, seven years was much too short a period from which 
to fix the average annual rainfall for all time, and recourse was 
then had to the observations from all the adjoining districts, which 
had been kept for a long period, including the seven years in 
question. 
The result of comparing these, showed that the average annual 
rainfall during the seven years was about 4 per cent, less than the 
average during periods varying from fifty to sixty years at the places 
where the records had been kept, and consequently this proportion 
was added to the amount of rainfall obtained from the actual 
gaugings on the drainage area, thus bringing the average annual 
rainfall as over a long period up to 65 inches. 
To arrive at the available annual rainfall, there was then 
deducted from this quantity 12 inches — as fixed by Mr Mansergh, 
F.R.S., after a reference to him — to reduce the quantity to the 
average of the three driest consecutive years, and a further 
quantity of 15 inches, which had been agreed on by the 
authors as the amount represented by evaporation and absorp- 
tion, leaving 38 inches as the average amount of the available 
annual rainfall. 
The extent of the drainage area is 6180 acres, and this gives a 
daily amount of 14,598,000 gallons, one-third of which has to be 
given off as compensation, and the remainder being appropriated 
for the purposes of supply. 
The following points may be noted in connection with the 
gaugings : — 
At the three stations where both daily and monthly readings 
have been kept the two sets of readings agree very closely indeed. 
The average annual rainfall at stations 5a, 6a, and 7a, where daily 
readings were recorded, was 6 TOO inches, while the corresponding 
amount from the monthly readings was 6T01 inches. 
The number of days on which no rain fell was — at 5a, 1036, or 
40*53 per cent. ; at 6a, 1095, or 42*84 per cent. ; and at 7a, 1118, 
or 43*74 per cent. 
The days on which less than T l F of an inch fell were respec- 
