THE MEASUREMENT OF EAIN. Sff* 



That city is supplied with witer from the Pentland hiHs. 

 It is mainly collected in a large reservoir called the Glen- 

 corse reservoir, about 730 feet above the level of the sea, 

 which affords the means of ascertaining with the greatest 

 accuracy the quantity of water which flows into it from the 

 elevated tract of country above. The mean height of this; 

 collecting ground, which consists of 3820 statute acresy is 

 about 1100 feet above the sea, the summits varying from 

 1300 to 1500 feet. 



A rain gauge is kept at the Glencorse reservoir, the 

 mean rain of 1844, 1845, and 1846 being 37*403 inches — 

 the average for sixteen years is 37*067 ; the maximum (1836) 

 49*080 ; the minimum (1842) 25*675 inches. 



From the 1st December 1846 to the 3 1st March 1847, 

 there came into the reservoir a quantity of water equal to 

 a depth over the whole drainage ground of 4*53 inches : the 

 rain during the same period as registered by the rain 

 gauge being 4*35 inches. 



This period was remarkably dry in Scotland, the mean 

 of sixteen previous years being 11*442 inches, and the mean 

 of the four lowest G*150 inches. 



Here is an instance, from the most accurate measure- 

 ment, of the flow of water exceeding for four months the 

 fall of rain. The gauge is certainly placed at the lowest 

 point; but the fall of rain was so small, that a larger propor- 

 tion than usual would be lost by absorption and evaporation. 

 The feet must be accounted for by supposing that the fall 

 of rain was much heavier in the highest parts of the district, 

 as the springs alone, unswollen by rain, would not have" 

 yielded the quantity. 



In another more elevated part of the Pentland hills, the 

 Bonally district, the fall of rain from the 1st of December 

 1846, to the 28th February 1847, was 4*71 inches; the pro- 

 duce 4*55 inches: this was ascertained by repeated gaugings. 



