178 On Canal Levels. (Marcu, 
2. A synoptic view of the rise and fall of several canals in con- 
nexion, without any regard to their respective length, which the 
first chart will show. (Plate LXJIL.) 
3. A section of the canal communication from the Mersey at 
Runcorn, to the Thames at Brentford, showing both the length 
and the lockage. (Plate LXIV.) 
In the second chart I have taken as zero the summit of the 
Birmingham Canal, which is at Smethwick, about three miles from 
Birmingham, ~and continues to. Wolverhampton. ‘This point is 
chosen on account, of the central situation of the Birmingham 
Canal, its connexion with other canals, the height of the summit, 
and because the water from that summit falls, part of it into the 
Irish Channel, and part into the German Ocean. 
The authority on which the rise and falls.of the several canals are 
taken is stated, that any correction, if requisite, may be made 
with greater facility. 
Amongst the documents which have heen consulted are— 
Smeaton’s Canal Reports; General History of Canals, by John 
Phillips, 1803; Carey’s Navigable Canals of Great Britain; 
A. Smith’s Map of Canals, 1815 ; Jos. Plymley’s Agricultural 
Report of Shropshire, in which the article of Canals was furnished 
by Thomas Telford; Rees’s Cyclopedia, article Canals, 1805 ; 
Sutcliffe on Canals, 1816; a great variety of surveys and plans of 
canals; private correspondence, and official information. 
If observations were made with Sir Henry Englefield’s baro- 
meter, at various situations, on different canals, on the same days, 
viz. on March 31, June 30, Sept. 30, and Dec. 31, and at the 
same time, would not they afford some confirmation of these 
surveys, or lead to some further investigation ? 
Information on the following heads is among the desiderata on 
this subject :— 
1. The level of the sill of the lock of the Grand Junction Canat 
at Brentford (in reference to the summit at Tring), instead of the 
present reference to high water mark in the Thames. 
2. The level of the sill of the lock of the Duke of Bridgewater’s 
Canal at Runcorn, where it joins the Mersey, in reference to the 
sill of George’s Dock at Liverpool ; and the level of the sill of 
George’s Dock, in reference to the surface of the water in the basin 
of the Leeds and Liverpool Canal at Liverpool. This would furnish 
a series of levels from London to the River Aire, at Leeds; and 
give fixed points more certain than any which refer to the tides; 
and at the same time would afford the means‘of adverting to the 
high and low water marks as a secondary and additional reference. 
3. The rise of the Thames from the sill of the lock at Brentford 
to the River Kennet near Reading, and from thence to the sill of the 
lock of the Kennet and Avon Canal at Newbury. This would 
connect the Kennet and Avon, the Wilts and Berks, the Thames 
and Severn, and the Somerset Coal Canals. 
