38 BATHYMETRICAL SURVEY OF 



50 to 60 inches, 

 60 ,, 70 ,, 

 70 80 ,, 

 80 90 

 90 100 

 100 110 ,, 



Total 12,737,328,000 



The results obtained by these three methods may be summarized 



Vennachar catchment. Lubuaig catchment. 



First method ... 14,857,214,000 15,600,760,000 



Second ... 14,991,815,000 15,750,446,000 



Third ... 12,424,867,000 12,737,328,000 



Mean ... 14,091,299,000 c. ft. 14,696,178,000 c. ft. 



Since Loch Katrine has been made use of by the Glasgow Corpora- 

 tion as the source of the water-supply to that city, a record has been 

 kept of the amount of water flowing out of Loch Vennachar or rather, 

 a record has been taken twice a day of the depth of water flowing over 

 a weir at Coilantogle, from which the quantity of water discharged may 

 be calculated. When the height of the water on the weir exceeded 5 

 inches, the weir became a drowned weir, so that it was difficult to 

 estimate the outflow, as there was a considerable velocity of approach, 

 especially during floods. 



Mr. Gale has kindly supplied us with the readings, taken twice a 

 day during the year 1869, of the depth of the outflowing water at 

 Coilantogle, and from these figures the outflow has been estimated for 

 that year at 9,572,000,000 cubic feet. The year 1869 was the driest 

 year during a period of twenty-four years, and we are not satisfied that 

 this computation can be accepted as a very correct estimate of the out- 

 flow from this catchment-basin even for that year. It would have been 

 interesting to have calculated the outflow for twenty-five years in the 

 same way as we have done for the year 1869, and to have taken the 

 mean. However, accepting the above estimate for the year 1869, and 

 adding to it the quantity of water supplied to Glasgow for that year, 

 which, from Mr. Gale's table showing the average amount of water 

 supplied per day during the first six months of the years 1866 and 1871, 

 may be taken at about 1,659,300,000 cubic feet, we find that the mean 

 rainfall exceeds the outflow in this year by 



According to the first method 3,625,914,000 cubic feet. 



second 3,760,515,000 



third 1,193,567,000 



Or a mean of 2,859,999,000 ,, 



Leslie* made experiments for twenty consecutive years on the 



* See Jour. Scot. Met. Soc., vol. v. p. 108, 3878. 



