between each of which there is a filter, which deprives the water, in its passage, of all the impurities it contains.

The cast-iron pipes, through which the water is conveyed through the streets, measure 983 miles. The two mains, leading from the reservoirs to the town, are 22 inches in diameter, while those laid in the streets are only from 3 to 12 inches. The pipes are connected together by spigot and faucet joints. The average cost of the mains and pipes was 7s. 1d. per lineal

foot.

Wherever water-power can be substituted for that of steam, a great saving will be effected.

The town of Richmond, in Virginia, is supplied with water from the James river, in the same manner as at Philadelphia. In these works two wheels are employed, which raise the water 160 feet into two reservoirs, measuring 194 feet in length, 104 feet in breadth, and 10 feet 8 inches in depth, and which therefore are capable of containing upwards of two millions of gallons of water. The water is made to pass through two gravel filters, which purify it. The water falls on the wheels from the height of ten feet, the diameter of each being eighteen feet, and breadth ten feet. The barrels of the two force-pumps are nine inches in diameter, the length of stroke being six feet. When only one wheel is at work, 400,000 gallons of water are raised in 24 hours.

The cast-iron main, leading from the pumps to the reservoir, is eight inches in diameter. The works cost about £20,000.

The city of Limerick was for a long time very badly

supplied with water; the quantity being scanty, and the quality of the very worst description. The condition of the city, however, is now somewhat improved in this respect. In or about the year 1834, a company was formed, called the "Limerick Pipe-water Company," and incorporated by act of parliament, for the purpose of supplying the city with water. Pipes are laid down through the entire city, but the inhabitants, in numerous instances, do not take advantage of the supply, being under the impression that the company's charges are too high, and the quality not of the best. The tank which supplies the city is about a quarter of a mile from it, and commands a sufficient height for the water to flow into all the houses. The supply is procured from the river Shannon, at Plassy, about a mile from the city, and forced thence to the tank, a distance of about a mile, up an inclined plane, the force employed being two steam-engines of twenty horse power each.

It would have been better to have brought the water from the Ballysimon wells, distant two or three miles from the city, which would afford a sufficient supply of the purest water.

The city of Cork is supplied with water from the river Lee. The water is raised from the river into a reservoir near Sunday's Well, which commands the city; the pumps employed being worked by two large wheels, which are turned by the stream.

The town of Belfast has long felt the want of a sufficient supply of water; depending, in a great measure, on the uncertain and scanty supply afforded by the

water carts.

This town might be abundantly supplied from the streams descending from the neighbouring heights. It is probable there may be some legal difficulty in applying these streams to the use of the town. If some vested right did not prevent their application to so useful a purpose, it is to be supposed that the spirited inhabitants of that rising town would not have suffered a want of such magnitude to exist, without having long ere this supplied it.

The City of Dublin is supplied with water from the Grand and Royal Canals, the former supplying that part of the city lying south of the River Liffey, and the latter that on the north side. In the immediate neighbourhood of the city are two basins, fed from the canals, the one on the north, and the other on the south side. In these basins the water is filtered, and from them conducted through metal pipes to the different streets, for the use of the inhabitants. The quality is good, and the quantity sufficient for culinary and other domestic purposes; but in cases of accidents by fire, the supply is lamentably deficient. The want of an ample quantity of water, and a systematic or properly organised plan to arrest the progress of the destructive element, are in most instances the cause of the loss of much valuable life and property, which a more abundant supply, under better management, might have prevented.

To compute the quantity of water that passes through a bridge or any section of a river.-Procure a slender wooden rod, to one end of which attach a weight sufficient to sink it, leaving the other end above the water. This being put into the stream whose

velocity is required, the greater velocity at the surface will make it incline towards the direction in which the water runs, and therefore, when it has acquired an equilibrium, it must move in an oblique position, the velocity being pretty nearly equal to that of the water at that place. As the velocity of the stream varies with its depth, the experiment should be tried in different parts of the cross-section, and a mean of all taken for the mean velocity. Now, having ascertained the mean velocity of the stream, the next thing to be done is to find the area of the cross-section, by taking the depths at several places, at equal distances across the stream. In making these experiments, a stop-watch, which tells the time to seconds, is necessary. M. Pitot invented a Potamometer, or stream measurer, which is by far the best for ascertaining the velocity of water. It consists of a tube of glass bent at right angles, the shorter branch being funnel shaped at the mouth, and the longer branch raised vertically to exhibit the elevation of the water in the tube, which corresponds to its velocity. The scale on the vertical branch is graduated by the following rule:

To find the height due to a given velocity, square the velocity per second, and divide by 64; the quotient will give the required height in feet. "On this principle, the divisions on the scale of the potamometer for miles, would be numbered at the following heights above the surface, in inches:

Divisions 1 2 3 4 5 6 7 8 9 Heights .4 1.6 3.6 6.4 10 14.5 19.7 25.8 32.7 Doctor Gregory says that "a similar instrument, made partly of tin, and cemented to a tube of glass,

might be introduced into a ship or steam-boat, for measuring the ship's way at sea, or for ascertaining the velocity of the steam-boat. If introduced into the cabin, the passengers could tell, by consulting the scale, the rate per hour at which the vessel was sailing, and consequently how soon they were likely to reach port."

To illustrate this, let us suppose the breadth of the river to be 60 feet, and the depths at six different equidistant places, to be 2, 4, 5, 7, 5, 3 feet, the first and last being the depths at the banks. Here 2+3=5, and 5÷2-21; then (23+4+5+7+5)÷5=231÷ 5=476, and 4×60=282 square feet for the area of the cross-section. If we now suppose the velocities taken at six different places, in the cross-section, to be 50, 56, 60, 70, 60, 54 feet per minute, the mean velocity will be (50+56+60+70+60+54)÷6=350 ÷6=58 feet, for the mean velocity per minute: then 282×581=16450 cubic feet, the quantity that flows through the section of a river in one minute.

To find the force of water impinging directly against a plane surface.-Multiply the area of the surface in feet, by the square of the velocity in feet per second, and the product, diminished by th part, will be the force required in lbs. nearly. If we suppose the velocities in feet, per second, to be 1, 2, 3, 4, 5, 6, 7, 8, 9; the forces in Ibs. upon one square foot of surface, will be 1, 4, 9, 151, 24, 35, 482, 621, and 79fbs. respectively.

When the velocity is given in miles per hour; you multiply the area of the surface in feet, by the square of the velocity, and double the product increased by th part, for the force required in lbs. nearly. If we