Rain-fall at different points on the same Mountain-Hang e, 447 



September, October, and November 1845, and for the period 

 consisting of these four months. The ratios for the several 

 months in the fourth column of this table show a much less 

 extent of deviation from the mean ratio of one to one and a 

 quarter than those for shorter periods ; and in them also is evi- 

 dent a tendency to increase on the approach of winter. 



11. It is a question of some interest whether the excess of the 

 rain-fall at the gauge G above that at the gauge H is principally 

 caused by the greater elevation of the ground at the former 

 gauge, or by the greater proximity of the gauge G to the chain 

 of summits of the mountain range. 



In order to throw some light on this question, there are added 

 in the fifth column of Table II. the depths of rain, as published 

 by Mr. Beardmore during the four months referred to, at a gauge 

 which I have designated by F, 734 feet above the sea, situated 

 near the embankment of the Edinburgh Water Company in the 

 gorge of the Valley of Glencorse, and in the immediate vicinity 

 of some of the highest summits of the range. In the sixth 

 column are given the ratios of the depths of rain at the gauge F 

 to those at the gauge H for the four months separately, and for 

 the whole period. 



From these data it appears, that although the gauge F was at 

 nearly the same elevation with the gauge H, it received during 

 the four months in question a depth of rain somewhat greater 

 than that at the gauge G, nearly 200 feet higher. This was 

 most probably the effect of the greater proximity of the gauge F 

 to the highest summits of the range. 



The ratios of the depth of rain at F to that at H for the dif- 

 ferent months vary in a very irregular manner ; probably because 

 those points are separated by the mountain-range, and receive 

 the rain-fall of different masses of cloud and different winds. 



12. In the third table the total depths of rain-fall during the 

 four months at each of the gauges H, G, F, are compared with 

 the depth registered in a gauge denoted by E during the same 

 period at the residence of Mr. Adie, immediately to the south of 

 Edinburgh, and a little more than 200 feet above the sea. The 

 rain-fall at this last point is very much less than that at any one 

 of the points on the mountain-range. 



13. The rain-fall at points still nearer the summits of the 

 hills than the gauges G and F must have been considerably 

 greater than that indicated by these gauges. This appears from 

 the facts, that the total flow of water during the period of obser- 

 vation, of a tributary stream of the river Almond, gauged by me 

 at a point near G, corresponded to an effective depth of rain-fall 

 only one-thirteenth part less than that recorded by the rain- 

 gauge; and that the flow from the valley of Glencorse, as gauged by 



