THE FRESH-WATER LOCHS OF SCOTLAND. 37 



based upon the mean height, which gave a total annual rainfall of 

 14,857,124,000 cubic feet. 



Applying the same method to the entire catchment-basin flowing 

 out of Loch Lubnaig, we arrive at the following result : 



Cubic feet. 



Levels of lochs to 500 feet, 6 '82 square miles x 74 '6 inches = 1,181,982,000 



500,, 750 7-15 x 77-9 =1,293,991,000 



750,, 1000 9-05 ,, x 82-7 =1,738,769,000 



1000,, 1250 ,, 970 x 87-4 = 1,969,568,000 



1-250,, 1500 9-89 x 92-2 =2,118,434,000 



1500 ,,1750 9-43 x 97 O =2,125,060,000 



17.50,, 2000 8-06 x 1017 ,, =1,904,337,000 



2000 ,,2250 6-64 x 106'5 =1,642,879,000 



J-J50,, 2500 3-30 x 111-3 = 879,148,000 



2500,, 2750 ,, 1-88 x 116'1 = 507,081,000 



_>7.->0 3000 1-02 x 120-8 = 286,256,000 



Over 3000 ,, 0-35 x 126 '6 = 102,941,000 



Total 15,750,446,000 



Here, again, there is a close agreement between the result obtained 

 by this method and that calculated from the mean height, which gave 

 a total annual rainfall of 15,600,760,000 cubic feet. 



A third method of estimating the amount of rain falling on any 

 particular region is afforded by drawing lines of equal rainfall, measur- 

 ing the areas between the lines, and multiplying by the mean annual 

 rainfall. Where the lines are based upon sufficiently numerous records 

 of rainfall at various heights, this method should give excellent results ; 

 but in the cases under discussion the number of observing stations is 

 small, and the majority of the rain-gauges are situated on the low-lying 

 grounds, only two being placed at heights exceeding 1000 feet, both 

 at 1800 feet : therefore the figures obtained in these cases are most 

 probably below the truth. Nevertheless, we have attempted to lay 

 down the lines of equal rainfall from the available records, as shown 

 on the accompanying rainfall map (see Plate III.). The areas enclosed 

 by the lines of rainfall have been measured with the planimeter, and 

 the rainfall calculated for the Loch Vennachar catchment-basin, with 

 the following results : 



Cubic feet, 



50 to 60 inches, 12 '35 square miles x 55 inches = 1,578,040 000 

 60 70 28-97 x 65 = 4,374,714,000 



70 80 18-93 x 75 = 3,298 372,000 



80 ,, 90 8-55 x 85 = 1,688,400,000 



90 ,, 100 ., 4"21 , x 95 = 929,166,000 



100 110 ., 2-28 ,, x 105 = 556,175,000 



Total 12,424,867000 



In like manner, the rainfall has been calculated for the Loch 

 Lubnaig catchment-basin, with the following results : 



