166 OBSERVATIONS ON THE FALL OF RAIN. 
ascertain the quantity of rain which fell in a moun- 
tainous district, and how much water could be 
collected in the basins of the reservoirs. 
The Lough Island Reavy Reservoir is situated 
on the westerly flanks of the Mourne Mountains, 
at an elevation of about 400 feet above the level 
of the sea. It derives its supplies from about 
3300 statute acres of mountain land, rising in 
places to abrupt eminences of from two to 3000 
feet in height. The direction of the general chain 
of the mountains is from north-east to south-west, 
and measuring from Carlingford Bay on the south, 
to Dundrum Bay at the foot of Slieve Donard, 
on the north, about 15 miles in length. They 
form the easterly sea-bord of the island, rising 
abruptly from the sea, the summit of Slieve 
Donard 2796 feet in height, the highest in the 
range, being only one mile and three quarters 
from the coast. Their average width is about 
five or six miles, the interior of the country for 
some distance from their westerly base, being 
comparatively level, rising to no great elevation 
above the level of the sea. In these mountains 
the River Bann and its early tributaries take 
their rise, within six or seven miles of the sea, 
from which they run in a westerly direction to- 
