river bed. But this condition of things can never be reached on the Mississippi River, and hence the concentration of flood volume will ever be harmful rather than helpful.

It follows from this, that if an additional quantity of water is confined to the channel in time of flood, we must provide accommodation for it at the surface rather than at the bottom of the river. If this point be settled, it is not difficult to approximate to the new stage to pass the new volume. There are many stations on the river below Cairo where discharge observations have been conducted for one or more years. If, for one of these sections, we plot stage and discharge, we get a curve showing the relation of the two from low water to say 50 feet above. If the levees be near the banks, which they usually are, and they be high enough to confine the flood, the conditions of flow will not be materially changed as the water gets above the bank. If, now, we know what the additional quantity will be to confine it all, we could simply extend the discharge curve until we reach the proper volume, and then read off the corresponding stage. The only uncertainties here are in the curve itself, which may not rigidly apply for another year at the same locality, and in its extension. These uncertainties may have a maximum value of several feet, and yet it is the only argument we can use, and it will give approximate results, which are more likely to be too small than too large. If the heights of levee necessary to confine such a flood as that of 1882 be found in this way, and the additional cost estimated, it makes an item of over $50,000,000, to complete the levee system from Cairo to the Gulf. It is questionable if such levees ever will be built.9

In regard to putting the levees farther from the banks, the two main objections have already been mentioned. There would be also little advantage from increased facility of discharge. The ground would have to be kept clear of all timber, weeds, and undergrowth, or else, it would offer very poor opportunities for discharge. This could hardly be done. The water flowing across a neck, also, does more to hinder than to help the flow around the bend, by lessening the volume in the channel.

There is another expedient which has been advocated, which appears to be practicable, but for which there are yet not sufficient

The Miss. Riv. Com., in their report for 1883, estimate this cost at some $11,000,000 but Gen. C. B. Comstock, President of the Commission dissents from this view.

surveys to determine. It consists in having ordinary sized levees, such as are now built, which will confine the ordinary floods, with waste weirs at such points as offer the best facilities of discharge through the swamps, to let off the surplus waters without detriment to the levees and with the least possible damage to the lands. There are a great many natural outlets from the river back to the main drainage channels of the bottoms, which could be utilized in this way. This sort of outlet, however, is more like the spilling of the water over the bank, than like a crevasse in the levee. These weirs would have to be miles in extent so that the depth of overflow need not be more than two feet. This arrangement has been adopted on the Rhone with very satisfactory results.10

The relation of levees to low water navigation has already been trenched upon above in showing the effect of increased stages at time of high water, in building up the bars. What is wanted is the removal of the bars, and for this purpose the low water energy should be increased and the high water effect diminished. In other words, the extremes should be brought nearer together which is all included in the term equalization of volume. Any influence, therefore, which forces these extremes farther apart is hurtful. Levees tend to make high water higher, and therefore, they are an injury to navigation.11

Evidently it would be of no advantage to navigation if the river bed were uniformly lowered a hundred feet, provided the same irregularities remained in the matter of pool and shoal.

If ever the river should be regulated in width so that the discontinuous movement of sediment becomes inappreciable, then the stage may be increased to advantage. It is highly improbable that this ever will be done, and therefore the building of levees on the banks of the Mississippi River will never prove an aid to low water navigation. On the contrary they will always tend to produce a certain amount of damage.

10 See paper by the writer on "Protection of Lower Mississippi Valley from overflow" in Journal of the Association of Engineering Societies, v. 3, p. 169.

11 See paper by Robt. E. McMath on "Levees, their Relation to River Physics," in Journal of the Association of Engineering Societies, v. 3, p. 43,

STEAM-ENGINE PRACTICE IN THE UNITED STATES IN 1884. By J. C. HOADLEY, C.E., Boston, Mass.1

FOLLOWING the usual course of development which rules in all untrammelled, healthful industries, no less than in the works of nature, the steam-engine is daily becoming more and more differentiated, the better to adapt each special form to some particular purpose.

As the machinist's tools used in its construction are specialized and adapted each to a single class of operations, — their increased efficiency for a special purpose more than compensating for the limited range of their utility, so the steam-engine itself, broadly considered, is continually developing new and useful varieties. At the same time, and as a consequence of the earnest study devoted to each variety, a parallel tendency to fixedness of type in each class is no less apparent than is the diversity of types.

Pumping-engines for public water-works, with a few large engines for manufacturing and mining purposes, constitute a class by themselves.

Engines for rolling-mills and general metallurgical purposes form a well-marked class.

Great lumber-manufacturing regions, like Maine and Michigan, have called into being a class of engines particularly adapted to saw-mills and wood-working machines.

Marine engines constitute an important class, of which steamboat and ferry-boat engines are one distinct variety, and engines of shipsof-war another.

--

Locomotives form a distinct class, subdivided into several varieties more or less differentiated, passenger-engines, freight-engines, mountain-engines, shunting-engines, and various small engines for mining and other purposes.

1 The stereotype plates of this paper were furnished by the author. EDITOR.

A. A. A. S., VOL. XXXIII.

The hoisting engine, the steam-crane, the steam-pump, the steamblowing engine, the steam fire-engine, the portable and the semi-portable engine, the traction-engine, are, each and all, clearly marked varieties.

The steam-ploughing-engine, a type highly developed in England, is almost unknown in the United States.

Engines specially designed for driving dynamos, for electric lighting, may almost be said to constitute a class of the quickrunning, or high-speed, group of engines.

Nearly all these classes of engines are in full course of development in the United States at this time, some much more advanced than others, but for the most part in a highly specialized form already, and rapidly taking on greater fixedness of type.

A complete and discriminating notice of all would require a voluminous treatise. The limits of this paper will admit only a few conspicuous examples of some of the leading types; and the time at command will compel a pretty close adherence to the observation and experience of the writer, with the risk of some lack of symmetry and proportion as a probable consequence, and of some apparent egotism.

WATER-WORKS ENGINES.

This classification is rather arbitrary; since it is intended to include only compound engines of a certain type, and to cover certain Corliss and Leavitt engines not used for water-works.

Examples of these engines are to be found in the public waterworks at Lowell, at Lynn, and at Lawrence, and at the sewagepumping station, Boston, Mass.; at the water-works in Providence and Pawtucket, R.I.; at St. Louis, Mo.; and at Saratoga, N.Y.

Engines belonging to this class, although not used for pumping, are the great Centennial Corliss engine, now supplying power for the car-shops at Pullman, near Chicago, Ill.; and the Leavitt engine at the Calumet and Hecla copper-mine, at Calumet, Houghton County, Mich.

LOWELL PUMPING-ENGINE.

This is a vertical, compound engine, having its steam-cylinders and air-pump located on one side of the beam-centre, and its pump and fly-wheel on the other side. The high-pressure cylinder is 36 inches in diameter, with a stroke of 5 feet 1 inches. The lowpressure cylinder, which is located at the extremity of the beam, has a diameter of 57 inches, with 8 feet stroke.

In volume swept through by the pistons, the two cylinders are to each other in the ratio of 1 to 3.9. The air-pump is 25 inches in diameter, with a stroke of 3 feet.

The water-pump, of the Thames-Ditton, or bucket-and-plunger variety, has a stroke of 6 feet, with 36 inches diameter of chamber and 25.45 inches diameter of plunger. The fly-wheel is 25 feet in diameter. The beam is double, and its top is 29 feet 1 inch above the floor of the engine-room.

The contract requirements were: 75,000,000 pounds raised 1 foot for each 100 pounds of coal burned in the boiler furnaces, equal to 2.64 pounds of coal per dynamic horse-power per hour, and a capacity of 5,000,000 Winchester gallons (of 231 cubic inches each) in 24 hours, when making 113 double strokes per minute.

It can be safely and conveniently run at velocities ranging from 5 to 16 revolutions of the fly-wheel per minute. The actual, or static head, is 159 feet; and the virtual, or dynamic head, when the engine is making 9 revolutions per minute, is 161 feet.

This engine was tested, for duty and capacity, by a board of experts, consisting of Mr. James B. Francis, Mr. William E. Worthen, and the writer, in July, 1873, by a run of 80 consecutive hours; and gave a duty of 93,002,272 foot-pounds per 100 pounds of coal burned, and 191.8 mean indicated horse-power, with a mean consumption of 351 pounds of coal per hour, equal to 1.83 pounds of coal per indicated horse-power and per hour.

This engine was constructed by Henry G. Morris of Philadelphia. Its subsequent performance has been still better. During 10 years and 4 months, from Sept. 1, 1873, to Dec. 31, 1883, the duty in foot-pounds per 100 pounds of coal burned for pumping, without deduction for ashes or clinkers, ranged between the annual mean of 108,699,620 and 89,739,070, with a general mean of 98,092,883.

During 5 consecutive years, 1875-1879, the mean duty on the same basis was 104,155,452.

During 9 years, 1875-1883, the duty in foot-pounds per 100 pounds of coal burned for all purposes, including warming the engine-house when not pumping, without deduction for ashes or clinkers, ranged between the annual mean of 72,925,000 and 78,757,528, with a general mean of 77,017,984.

PUMPING-ENGINE, LYNN WATER-WORKS.

This engine, designed by Mr. E. D. Leavitt, jun., and built by I. P. Morris & Co. of Philadelphia, in 1873, presents some features then quite novel, but since often repeated.