HISTORY OF

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will be of moment. These can be fixed upon only by an accurate sur-vey and knowledge of the country through which the canal is intendedto pass.

2clly. The supply of water*

It is almost needless to mention the absolute necessity of a supply ofwater for a canal, which must be in requisite quantities in the summit,or reservoirs, which may be supplied by the neighbouring springs; or,if these fail, water must be thrown up by engines from a lower level.

A

Reservoirs are large bodies of water collected together for theuse of such parts of the canal as are likely to be deficient; into which itis let by sluices, when and where wanted.

The quantity of water requisite for the use of a canal depends in agreat measure upon the quantity of trade carried on. A lock full ofwater must be lost every time a boat passes through, which, in a lockwhose length in the chamber is 75 feet, breadth 7 feet, and lift 6 feet,will be 125 cubic yards of water; which quantity, multiplied by thenumber of boats likely to pass through the summit lock, will give an ideaof the waste of water. Allowance also must be made for exhalationand accidents.

3dly. The mos eligible levels.

The most eligible level is certainly that which has the least fall andthe fewest obstructions, and is best adapted to the face of the country.

4thly. The nature of the ground to be cut through.

The soil most favourable for a canal is clay; the most unfavourable,sand. As foils approach more or less to the quality of clay or sand, insuch proportion are they to be preferred for holding water.

5 thly.