Rain-fall at different points on the same Mountain-Range. 445 



daily and simultaneously for a period of 151 consecutive days, 

 from the ISth of July to the 12th of December 1845^ at two 

 points on the north-western slope of the Pentland Hills near 

 Edinburgh. The long lapse of time previous to their publication 

 has been occasioned by the fact, that the fair copy of the obser- 

 vations, with various calculations founded on them, accidentally 

 passed out of my possession not long after it had been prepared ; 

 and it was only a short time since that I happened to find the 

 original registers, which 1 have reduced anew. 



3. The range of the Pentland Hills extends in a north-east 

 and south-west direction for about thirteen miles. Its north- 

 east extremity is about five miles from Edinburgh towards the 

 south, and seven miles from the Frith of Forth. For about four 

 miles in the middle of its course the range is double, consisting 

 of two parallel chains of summits separated by a deep and nar- 

 row valley called Glencorse, from which a considerable portion 

 of the water-supply of Edinburgh is derived. This valley is tra- 

 versed by a stream which runs towards the north-east, then 

 turns at right angles and escapes towards the south-east through 

 a gorge, now occupied by the embankment of one of the reser- 

 voirs of the Edinburgh Water Company. 



4. The summits of the Pentland Hills vary from 1400 to 

 1900 feet in height above the sea; the ridges between them, 

 from 1000 to 1300 feet. The highest summits are in the double 

 chain, near the middle of the range. 



5. The south-west extremity of the Pentland Hills is a point 

 of divergence of tributary streams of the Forth, Clyde and Tweed. 

 To the west and south-west of this point rise some small tribu- 

 taries of the Clyde. From the south-eastern face of the hills, 

 near the point of divergence, flow some tributaries of the Tweed ; 

 further towards the north-east and from the central valley, tri- 

 butaries of the Frith of Forth. On the north-western face of 

 the range are the sources of the water of Leith and some smaller 

 tributaries of the Frith of Forth ; and on the same face, near its 

 south-western end, some sources of the Almond, also a tributary 

 of the Frith of Forth. From the south-western extremity of the 

 Pentland range already referred to, a range of low hills of from 

 1000 to 800 feet in height extends towards the west-north-west, 

 being part of the boundary between the basin of the Forth and 

 that of the Clyde. 



\ 6. The surface of the Pentland Hills is covered chiefly with 



pasture and heath, with a few patches of peat. Ample details 



of the topography and geology of this range may be found 



in Mr. Charles Maclaren^s work on the Geology of Fife and the 



Lothians. 



. 7. The two points at which the observations of rain-fall now 



