ON THE INDUSTRIAL USES OF THE UPPER BANN RIVER. 145 
summer discharge allowed over Ervin’s Weir, or about 30 cubic feet per 
second (equal to two and a half horse-power to the foot fall at Sir William 
Fairbairn’s estimate of 12 feet in its best application to a water-wheel equal 
to one horse-power), has been granted for 2663 days, or, on an average, 
102 days yearly ; and the reservoir has only been empty 303 days, or, on an 
average, eleven and a half days yearly. The Corbet reservoir has been of 
much more service than its capacity would lead one to expect, as it may be 
filled and emptied four or five times in each year by small floods in the river, 
and all the Sunday’s water can be sent into it and let down to the mills on 
Monday and Tuesday. It is generally exhausted before the upper reservoir 
is called upon, and keeps up a supply when there is a scarcity in frosty wea- 
ther in winter ; and when a flood comes at the end of these short terms of 
scarcity it is ready to receive it, and thus diminish the amount of back water 
on the wheels. If its area were five or six times as great, it would be almost 
that much more valuable, as so many floods pass when it is full; for its 
drainage-area is about sixteen times that of Lough Island Reavy. According 
to the original plan, the embankment should have been raised so as to impound 
the water to a depth of 18 feet instead of 11 feet 3 inches, and contain 
46,783,440 cubic feet instead of 28,177,221 cubic feet ; unless, however, the 
intake from the river was at a much higher level, say at Linen Hill weir, it 
would not be much advantage, for the drainage-area of the lake itself is 
very small. 
The register of the Corbet reservoir has not been kept so long or as accu- 
rately as that of Lough Island Reavy, so it is not possible to show so well the 
service it has done the mills; from the average of three years, however, and 
compurison with the register of Lough Island Reavy, I calculate it has given 
120,000,000 cubic feet in the year, exactly one half that of Lough Island 
Reavy, or a good supply for fifty-one days; add this to the Lough Island 
Reavy supply, and there is a total of 153 days of twenty-four hours each. 
Sir William Fairbairn calculated that when all the reservoirs should be made 
(including the Deer’s Meadow and the full completion of the other two reser- 
voirs), there would be a supply of 60 feet per second for 108 days of twenty- 
four hours each year. Reducing it to 108 days, the supply really has been 
44 cubic feet per second, which is very nearly in the same proportion to the 
amount that can be impounded as his calculation was to that proposed to be 
impounded. As the supply from the reservoirs has only failed, on an average, 
eleven and a half days yearly, the standard water-power may be said to have 
been almost constantly maintained. This constancy in the supply makes the 
Upper Bann most valuable as a power; indeed it is almost as good as steam- 
power, but at a much less cost. 
Whilst the average value of water-power in Ireland is about £2 per horse- 
power per annum, on the Bann it may be estimated at £4 where only ten 
hours’ work per diem is available, and £7 where constant work is maintained 
after paying the water tax. Steam-power on the Bann costs about £6 per 
annum per horse-power, calculating 4 pounds of coal equal to one horse- 
power per hour. The first cost and maintenance of works necessary to render 
these powers available would be greater in the case of steam than water. 
More convenient mill sites can, however, be obtained for the application of 
steam than water. On the Bann it is found more economical to work steam 
and water in conjunction where much power is required, as advantage can be 
taken of moderate floods to ease the steam; this method of working is parti- 
cularly applicable’ to bleach-works, where the steam, after passing through 
the cylinder of a high-pressure engine, can be used for boiling and heating. 
1874. L 
