618 PRACTICE OF AGRICULTURE. Part III. 



examine all the canals and rivers with which the proposetl canal is to connect, and ascertain the widths 

 and depths thereof, the sizes of their locks, and of the vessels usually navigating them. 



3808. The dimensions, number, and kind of locks or inclined planes, length of levels, &c., may now be 

 determined on, and how far railways or branch canals or roads may be connected with the main line. 

 Many engineers, and especially Fulton, have warmly advocated the formation of small canals. On this 

 subject Chapman, a most judicious artist, observes, " that the system of small canals is particularly eligible 

 in all countries where limestone, coal, iron ore, lead, and other ponderous articles, not liable to damage 

 from being wet, or not likely to be stolen, are the objects chiefly to be attended to ; and where the declivity 

 of the country runs transversely to the course of the canal, which will generally be the case along the sides 

 of mountains, at an elevation above the regular ground at their feet. In those situations, the great falls 

 or inclined planes may be made at the forks of rivers, so that the upper levels may branch up both the 

 vales, and thus give the most extended communication. A situation suited for those canals will often 

 be found in countries that are not absolutely mountainous, but where the ground regularly declines to- 

 wards the vales or large rivers." 



3809. A rough section of the proposed line will enable the engineer to see the places of the heights, and 

 breadths of the various summits, or ranges of high land, that are to be passed, and whether any two or 

 more adjacent ones can be connected by a long summit level, without deserting any considerable town or 

 point of trade, which will diminish the difficulties of supplying the canal with water ; as every such junction 

 of summits preserves the water of two lockages, besides presenting so many more points at which the 

 canal can be supplied with water from springs and rivulets above its level, or where, in less favourable 

 situations, the same can be collected in a lower level, to be pumped up. From one end of the proposed 

 summit level it will be right now to proceed with the survey, tracing the level accurately, and marking 

 the same by pegs or stakes, that will last for some time, and be known by the surveyor, who is to follow 

 and make a plan of the line ; the levels being frequently transferred to what are called bench marks, upon 

 the trunk of a tree, a large post, or a building, the same being noted so particularly in the field or survey 

 book, that they may be readily found for years afterwards. We suppose the engineers, by this time, to 

 have settled the rise that each lock should have, according to the dimensions adopted for the canal, the 

 probable supply of water on the summit, and other circumstances ; the summit level will be traced as above, 

 till the proper place occurs for making a fall of two or more locks, at about 100 yards, or a little more from 

 each other; and the places of these falls being marked, the level is again to be pursued and traced from 

 the bottom of them, and marked out as before, till the opportunity occurs for another pair or more of locks, 

 or till some obstacle, as a gentleman's park, houses, gardens, orchards, mills, roads, &c. present themselves 

 at a distance ; when it will be proper, after transferring the level arrived at to a proper and permanent mark, 

 to proceed forwards, and to examine and well consider the different ways and levels, if more than one 

 present themselves, by which the obstacle can be passed. From the most confined part of the course for 

 the canal, owing to the obstacle, it will be right to level back, till the former work is met, and to determine 

 the most eligible mode of bringing the two levels together, upon the principles before stated; if they can 

 be applied, either by adding another lock, or taking one from any of the sets which had been before 

 marked out, as occasion may require, and marking out the new levels thereby occasioned : the line be- 

 tween the summit and the first obstacle, or confined part of the course, being thus adjusted, a new point of 

 departure is to be taken from such obstacle, and the level pursued as before, till the fall for a pair or more 

 locks can be gained, at the proper distance from each other. In this way, the patience, perseverance, and 

 abilities of the engineer must be exercised, until a practicable line of some length is obtained, and staked 

 out; when the assistant land-surveyor must follow, and make a correct and particular plan of the line of 

 the several proposed locks, embankments, tunnels, &c. upon the same, and of the several fields, or pieces 

 of land through which it passes, or that come within 100 or 150 yards of it in any part : it will likewise be 

 the business of the surveyor to ascertain, with the utmost care, the boundary of every parish and town- 

 ship; what county each is in ; the proper names of the owners and occupiers of every piece of land in 

 each, however small, upon or within that distance of the line, with reference to the same upon his plan ; 

 and to describe correctly all public and private roads and paths that cross or intersect the line, and to and 

 from what places they lead ; the course of all brooks or streams of water, and particularly such as lead to, 

 and contribute to the supply of, any mill : the situation of the houses and towns upon the line, or within 

 some miles of it, should also be determined ; the nearer they are the greater accuracy will be necessary. 

 A complete plan of the line, and all the projected collateral cuts, feeders, reservoirs, &c. being finished, 

 the engineer will enter on a most careful revisal of the whole scheme, with this plan in his hand ; on which 

 all the places where culverts or drains will be required are to be marked, as also the proper places for the 

 bridges, and the necessary alterations of the roads and paths, which will be cut off" by the canal, so that the 

 public may not be inconvenienced and turned long distances round about, and still, that as few bridges as 

 possible, and those in the least expensive places, may be erected. In some instances new channels will 

 require to be cut for brooks and water-courses, to a considerable extent, in order to save culverts, or bring 

 them to the most desirable spots. For proper security against accidental errors, the whole of the levelling 

 should now be gone over again, and the several bench marks compared, and renewed with the utmost 

 care by the engineer's assistants, while he is proceeding with the necessary enquiries and calculations for 

 an estimate of the whole expense of the undertaking. 



3810. The supplying of a canal with water, in a great number of instances, occasions no inconsiderable 

 share of the whole expense, either in the first cost of mills or streams of water ; in land for, and labour in 

 constructing, reservoirs, engines to pump water, &c. ; or annually, ever afterwards, in the fuel for, and 

 repairing of, engines ; hire of water from mills in dry seasons, &c. : this subject should, therefore, employ 

 the most sedulous attention of the engineer, to make the most economical use of what streams he finds, to 

 procure other supplies of water at the least expense, and above all, to secure abundance. The dimensions 

 and heights of the locks, and breadth of the canal, being settled, an accurate calculation should be made 

 of the quantity of water required to fill a lock ; and, with the largest probable number of boats that 

 will pass in a day, of the quantity required daily in every part of the canal : this, with a due allowance 

 for the evaporation, from the surface of the whole canal and its reservoirs, and for the soakage that will 

 take place into the banks, however well they are constructed, will show the number of locks full of water 

 that will be required, from the different sources. 



3811. In estimating the expense of all such works, it will be necessary to have the 

 lengths and solid contents of the several embankments, and the distance from which the 

 stuff or soil must be fetched for the same ; the lengths and dimensions of all the deep 

 cuttings, and the distance to which the stuff must be removed ; the lengths of the tun- 

 nels, and number and depths of the several shafts or tunnel pits ; the lengths or head- 

 ings of soughs that will be wanted to drain the tunnelling work : these, and all the 

 great variety of other works, some of which we have already mentioned and others we 

 shall have occasion to mention in the sequel, being particularly stated, and prices affixed 

 to each species of work and kind of material (which prices ought not to be below the 

 current prices of the best articles at the time, and due allowance should also be made for 

 the advance of prices which will take place during the progress of the work) ; the total 

 nrobable expense, with a due allowance for contingencies, will be thus obtained, on which 



