with the pump through it, as represented in the figure. To the centre of one or both ends of the case is screwed fast a thick piece of brass whose outline resembles that of the letter D: the flattened side is placed towards the butment and is so formed that the same distance is preserved between it and the opposite parts of the butment, as between its convex surface and the rim of the case. The pistons, as in the last figure, are rectangular pieces of stout metal, and are dropped into slits made through the rim of the drum, their length being equal to that of the case, and their width to the distance between its rim and the D piece. They are moved by a crank attached to the drum axle. To lessen the friction and compensate for the wear of the butment, that part of the latter against which the drum turns is sometimes made hollow; a piece of brass is let into it and pressed against the periphery of the drum by a spring.

In No. 138 the axis of the drum or smaller cylinder is so placed as to cause its periphery to rub against the inner circumference of the case. Two rectangular pistons, whose length are equal to the internal diameter of the case, cross each other at right angles, being notched so as to allow them to slide backwards and forwards to an extent equal to the widest space between the two cylinders. The case of this pump is not perfectly cylindrical, but of such a form that the four ends of the pistons are always in contact with it. An axle on the drum is moved by a crank. This pump, and another similar to it, were described in Bramah and Dickenson's patent for three rotative steam-engines in 1790. Rep. of Arts, vol. ii, 85. Fire engines have been made on the same principle.

Another class of rotary pumps have their pistons made somewhat like the vanes of wind mills. They were originally designed as steam-engines, and were, if we mistake not, first introduced by Hornblower, in the latter part of the last century. He employed four revolving vanes which were so arranged that, while one passed edgeways through a narrow cavity which it filled, the opposite one presented its face to the action of the steam. These machines have been variously modified as pumps, but generally speaking they are more complex and of course more liable to derangement than others: we have known two of them, fifteen inches diameter and apparently well made, (at a cost of 150 dollars,) which a friend used to force water to an elevation of twenty feet, become deranged, and thrown aside as useless in the course of three or four weeks.

A centrifugal forcing pump may be made by enclosing the arms of an atmospheric one, (such as represented at No. 95, page 229,) in a close

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Rotary Pumps.

291

drum or case, to which an ascending or forcing pipe is attached: the water would rise through the pipe, provided the velocity of the arms was increased according to the elevation of its discharging orifice. In place of tubular arms, two or more vanes radiating from a vertical axis and turned rapidly in the case would produce the same effect; the suction pipe being connected to the bottom at the centre and the forcing pipe to the rim or the top. Such pumps are in their construction simpler than other rotary ones, besides which no particular accuracy is required in fitting their working parts; nevertheless, they are as liable to derangement as others, for the velocity required to be given to the arms is so great, that the teeth of the wheels and pinions by which motion is transmitted to them

are soon worn out.

Centrifugal pumps like those just described have been tried as substitutes for paddle wheels of steam-vessels: i. e. the wheels were converted into such pumps by inclosing them in cases made air-tight, except at the bottom through which the ends of the paddles slightly projected; a large suction pipe proceeded from one side of each case (near its centre) through the bows of the vessel and terminated below the water line: by the revolution of the wheels water was drawn through these tubes into the cases and forcibly ejected below in the direction of the stern, and by the reaction moved the vessel forward.

It must not be supposed that the preceding observations include an account of all rotary pumps. We have only particularized a few out of a great multitude, such as may serve as types of the various classes to which they belong. Were a detailed description given of the numerous forms of these machines, modes of operation, devices for opening and closing the valves, moving the pistons, diminishing friction, compensating for the wear of certain parts, for packing the pistons, &c. &c., those readers who are not familiar with their history would be surprised at the ingenuity displayed, and would be apt to conclude that all the sources of mechanical combinations had been exhausted on them. We would advise every mechanic who thinks he has discovered an improvement in rotary pumps, carefully to examine the Repertory of Arts, the Transactions of the Society of Arts, the London Mechanics' Magazine, and particularly the Journal of the Franklin Institute of Pennsylvania, before incurring the expenses of a patent, or those incident to the making of models and experiments.

Rotary pumps have never retained a permanent place among machines for raising water: they are, as yet, too complex and too easily deranged to be adapted for common use. Theoretically considered they are perfect machines, but the practical difficulties attending their construction have hitherto rendered them (like rotary steam engines) inferior to others. To make them efficient, their working parts require to be adjusted to each other with unusual accuracy and care, and even when this is accomplished, their efficiency is, by the unavoidable wear of those parts, speedily diminished or destroyed: their first cost is greater than that of common pumps, and the expense of keeping them in order exceeds that of others; they cannot, moreover, be repaired by ordinary workmen, since peculiar tools are required for the purpose-a farmer might almost as well attempt to repair a watch as one of these machines. Hitherto, a rotary pump has been like the Psalmist's emblem of human life :-"Its days are as grass, as a flower of the field it flourisheth, the wind [of experience] passeth over it, and it is gone." Were we inclined to prophecy, we should predict that in the next century, as in the present one, the cylindrical pump will retain its preeminence over all others; and that makers of the ordi

nary wooden ones will then, as now, defy all attempts to supersede the object of their manufacture.

RECIPROCATING ROTARY PUMPS :-One of the obstacles to be overcome in making a rotary pump, is the passage of the piston over the butment, or over the space it occupies. The apparatus for moving the butment as the piston approaches to or recedes from it, adds to the complexity of the machine; nor is this avoided when that part is fixed, for an equivalent movement is then required to be given to the piston itself in addition to its ordinary one. In reciprocating rotary pumps these difficulties are avoided by stopping the piston when it arrives at one side of the butment and then reversing its motion towards the other; hence these are less complex than the former: they are, however, liable to some of the same objections, being more expensive than common pumps, more difficult to repair, and upon the whole less durable. Their varieties may be included in two classes according to the construction of the pistons; those that are furnished with valves forming one, and such as have none the other. The range of the pistons in these pumps varies greatly; in some the arc described by them does not exceed 90°, while in others they make nearly a complete revolution. They are of old date, various modifications of them having been proposed in the 16th century. No. 139 consists of a close case of the form of a sector of a circle, having an opening at the bottom for the admission of water, and another to which a forcing pipe with its valve is attached. A movable radius or piston is turned on a centre by a lever as represented; thus, when the latter is pulled down towards the left, the former drives the contents of the case through the valve in the ascending pipe.

Belidor has described a similar pump in the first volume of his Arch. Hydraul. 379. The case is a larger portion of a circle than that of No. 139, and the piston is furnished with a valve. A pump on the same principle was adopted by Bramah as a fire-engine in 1793: His was a short cylinder, to the movable axle of which two pistons were attached that extended quite across, and had an opening covered by a clack in each.

No. 140 consists of a short horizontal cylinder: a portion of the lower part is separated from the rest by a plate where the suction pipe terminates in two openings that are covered by clacks c c. The partition A

Chap. 6.]

Application of Pumps in Modern Water-works.

293

extends through the entire length of the cylinder and is made air and water tight to both ends, and also to the plate upon which its lower edge rests. The upper edge extends to the under side of the axle to which the piston B is united. One end of the axle is passed through the cylinder and the opening made tight by a stuffing box; it is moved by a crank or lever. Near the clacks c c two other openings are made through the plate, to which two forcing pipes are secured. These tubes are bent round the outside of the cylinder and meet in the chamber C where their orifices are covered by clacks. Thus when the piston is turned in either direction, it drives the water before it through one or other of these tubes; at the same time the void left behind it is kept filled by the pressure of the atmosphere on the surface of the liquid in which the lower orifice of the suction pipe is placed. The edges of the pistons are made to work close to the ends and rim of the cylinder by means of strips of leather screwed to them. Modifications of these pumps have also been used in England as fire-engines.

Reciprocating rotary pumps have sprung up at different times both here and in Europe, and have occasionally obtained "a local habitation and a name," but have never become perfectly domesticated, we believe, in any country. We have seen some designed for ordinary use that were elegantly finished, and decorated with gilding and japan-they resembled those exotic plants which require peculiar care, and are rather for orna

ment than for use.

Reciprocating rotary pumps have also been proposed as steam-engines. Watt patented one in 1782.

CHAPTER VI.

APPLICATION of pumps in modern water-works: First used by the Germans-Water-works at Augsburgh and Bremen-Singular android in the latter city-Old water-works at Toledo—At London bridge -Other London works moved by horses, water, wind and steam-Water engine at Exeter-Waterworks erected on Pont Neuf and Pont Notre Dame at Paris-Celebrated works at Marli-Error of Raunequin in making them unnecessarily complex. American water-works: A history of them desirableIntroduction of pumps into wells in New-York city-Extracts from the minutes of the Common Council previous to the war of Independence-Public water-works proposed and commenced in 1774-Treasury notes issued to meet the expense-Copy of one-Manhattan Company-Water-works at Fair Mount, Philadelphia.

BEFORE noticing another and a different class of machines, we propose to occupy this and the two next chapters with observations on the employment of pumps in "water-works," and as engines to extinguish fires -both in this country and in Europe.

The hydraulic machinery for supplying modern cities with water generally consists of a series of forcing pumps very similar to the machine of Ctesibius, (No. 120;) and when employed to raise water from rapid. streams, or where from tides or dams a sufficient current can be obtained, are worked like it by under or by overshot wheels. An account of old European water-works is an important desideratum, for it would throw light on the history of pumps in the middle ages, during which little or nothing respecting them is known. The older cities of Germany were the first in modern days that adopted them to raise water for public purposes; but of their construction, materials, and application under various circum stances, we have no information in detail. Rivius, in his Commentary on

the machine of Ctesibius, speaks of pumps worked by water wheels as then common, (A. D. 1548.) The hydraulic engines at Augsburgh were at one time greatly celebrated. They are mentioned, but not described, by Misson and other travelers of the 17th century. They raised the water 130 feet. Blainville, in 1705, speaks of them as among the curiosities of the city. He observes-"The towers which furnish water to this city are also curious. They are near the gate called the Red Port, upon a branch of the Leck which runs through the city. Mills which go day and night, by means of this torrent, work a great many pumps, which raise water in large leaden pipes to the highest story in these towers. In the middle of a chamber on each of them, which is very neatly and handsomely ceiling'd, is a reservoir of a hexagonal figure, into which the water is carried by a large pipe, the extremity of which is made like a dolphin, and through an urn or vase held by a statue sitting in the middle of the reservoir. One of these towers sends water to all the public fountains by smaller pipes, and the three others supply with water a thousand houses in the city; each of which pays about eight crowns yearly, and receives a hundred and twenty pretty large measures of water every hour." Travels, vol. i, 250. Misson's Travels, 5 ed. vol. i, 137.

Contemporary with the engines at Augsburgh was one at Bremen that is mentioned by several writers of the 17th century. It was erected on one of the bridges and moved by a water wheel it raised water into a reservoir at a considerable elevation, whence the liquid was distributed to all parts of the city. An old author when speaking of it, mentions an android in Bremen, a species of mechanism for which the Germans were at one time famous. At the entrance of the arsenal, he observes," stands the figure of a warrior arm'd cap-a-pe, who, by mechanism under the steps, as soon as you tread on them, lifts up the bever of his helmet with his truncheon to salute you."

There was also a celebrated water-engine at Toledo, the former capital of Spain. It raised the water of the Tagus to the top of the Alcazar, a magnificent palace erected on the summit of the declivity on which the city is built; the elevation being " five hundred cubits from the surface of the river." What the particular construction of this machine was we have not been able to ascertain, nor whether it was originally erected by the Moors who built the palace. It is mentioned by Moreri as a “wonderful hydraulic engine which draws up the water from the river Tagus to so great a height, that it is thence conveyed in pipes to the whole city;" but in the middle of the last century (1751) the author of the Grand Gazetteer, or Topographic Dictionary, remarks (page 1289) that this "admirable engine" was then " entirely ruined."

The introduction of pump engines into the public water-works of Eng land and France is sufficiently ascertained. This did not take place till long after they had been employed in Germany; and both London and Paris were indebted to engineers of that country for the first machines to raise water from the Thames and the Seine. Previous to their introduc tion, cities were commonly supplied from springs by means of pipes. As early as A. D. 1236, the corporation of London commenced to lay a six inch leaden pipe from some springs at Tyburn, a village at that time some miles distant from the city. This is supposed to have been the first at tempt to convey water to that city through pipes, and fifty years elapsed before the whole was completed. These pipes were formed of sheet lead and the seams were soldered: part of them was accidentally discovered in 1745 while making some excavations, and another portion in 1765. (London Mag. for 1765, p. 377.) In 1439 the abbot of Westminster, in whom