And sudden darkness shrouds the shatter'd

walls;

Steam, smoke, and dust, in blended volumes roll,

And night and silence re-possess the pole.

Garden engines are also constructed on a principle similar to that which we have been describing.

This figure is the re-ren presentation of a method

of raising water from

wells of

depth.

considerable

Emma. Is it a more

convenient method than

the wheel and axis?

Father. The wheel and axis are adapted merely to draw up water by buckets: whereas the rope-pump is intended to throw water into a reservoir to almost any height. It consists

of three hair-ropes passing over the pulleys A and B, which have three grooves in each. The lower pulley B is immersed in the water, in which it is kept suspended by a weight. The pulleys are turned round with great velocity by multiplying wheels, and the cords, in their ascent, carry up a considerable quantity of water, which they discharge into the box or reservoir z, from whence, by pipes, it may be conveyed elsewhere. The ropes must not be more than about an inch apart.

Emma. What is the reason of that, papa?

Father. Because, in that case, a sort of column of water will ascend between the ropes, to which it adheres by the pressure of the atmosphere.

Charles. Ought not this column,

in its ascent, to fall back by its own

gravity?

Father. Yes: and so it would, did not the great velocity of the ropes occasion a considerable refraction of the air near them, consequently the adjacent parts of the atmosphere pressing towards the vacuity, tend to support the water.

Emma. Can any considerable quantity of water be raised in this way?

Father. At Windsor, a pump of this kind will raise, by the efforts of one man, about 9 gallons of water in a minute, from a well 95 feet deep. In the beginning of motion, the column of water adhering to the rope is always less than when it has been worked for some time, and the quantity continues to increase till the surrounding air par

takes of its motion. There is also another of these pumps at the same place, which raises water from the well in the round tower 178 feet in depth.

Charles. Pray what is a chainpump?

Father. It consists of two square, or cylindrical barrels, through which a chain passes, having a number of flat pistons, or valves, fixed upon it, at proper distances. The chain passes round wheel-work, fixed at one end of the machine. A whole row of the pistons, which go free of the sides of the barrel, is always rising when the pump is at work; and, as this machine is generally worked with great velocity, they bring up a full bore of water in the pump.

Father. For what purposes is the chain-pump chiefly used?

Father. It has been used in the navy, to prevent the fatal accidents which have sometimes happened on shipboard by the choking of pumps

with valves.

Charles. Is it confined to nautical

uses?

Father. No, it is adapted to the raising of water in all situations, where it happens to be mixed with sand, or other substances, which destroy common pumps, as in alumworks; in mines; in quarries, &c. In its present improved state, it is simple and durable, and may be made of metal or wood at a moderate expense.

Emma. You told us, some time ago, that, when we had seen the nature, and understood the construction of valves, you would explain the action of the water-press.

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