The line of the river is very nearly thirty-four miles. More than one hundred and sixty bridges cross it- some of brick, some of iron, and some of wood. There are about sixty culverts that pass beneath its bed the various brooks and rivulets which it traverses in its course. The descent is about three inches to the mile. Both its depth and width vary the former seldom exceeding five feet, the latter averaging eighteen feet.

The springs which originally supplied this river, were, as has been before mentioned, in the villages of Amwell and Chadwell, in Hertfordshire. But these were found unequal to the increasing demand, and recourse was had to the river Lea, which runs in a copious stream near the new river.

An act of Parliament in 1738, authorised this use of certain portions of the waters

50 PREL1MINARYESSAY. of the Lea, on condition of a present sum paid down, and a perpetual annuity, for the improvement of the navigation of that river. The quantity of water to be abstracted from the Lea, was regulated by a balance engine of which the channel was 14 feet long, 6 broad and 2 deep.

When the reservoirs at New River Head, at Clerkenwell, are full, they stand at a level of eighty-four arid a half feet above high water in the Thames which, however, only ;

enabled the Company to fill the cisterns in the basement stories of the houses they supplied. Hence, in 1810, resort was had to steam engines to throw the water up, and then a head was thus obtained 144 feet above the level of the Thames, and high for enough the loftiest houses. Another consequence of employing the steam engine, was the replacing the wooden tubes through which the water was first conveyed, by iron pipes.