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gineer. Fig. 10 represents the shifting link motion, in mid-gear, at beginning of the back stroke. The origin of the link motion, in an impracticable form however, has been traced to a Mr. Williams of Newcastle; it was worked out by Mr. Howe, and applied to Stephenson's locomotives, and is generally accredited to Robert Stephenson. The motion attained is equivalent to that of a variable eccentric. If two eccentrics be differently set on the same axle, each will be the equivalent of a crank, giving to its rod a definite throw or stroke equal to twice the eccentric radius; and the movement of either eccentric in any part of its revolution can be resolved into two component motions, tangential and radial. Now, in the link motion, two eccentrics have their centres of form in nearly opposite directions from the same axle on which they turn, and their rods, instead of attaching to the valve rod, take hold of the upper and lower ends of a curved, slotted link; the valve rod by a stud or a pin within the slot can be so shifted as to be worked from either end of the link, or from intermediate points in its length. The motion of the link is compounded of the distinct motions of the eccentrics, which, as respectively intended to give forward and backward strokes, are called the fore and back eccentrics. The motion of each eccentric prevails in that half of the link to which it is coupled, the motion at middle point being equally composed of the two; so that the horizontal movement, distance of travel, or throw which the link will impart to the valve rod, is a minimum when the rod is actuated from the middle of the link, and increases toward the extremities, but with a movement in the two in opposite directions. The link is shifted, or the block and valve rod pin within it, by means of the reversing lever at the hand of the engineer; and thus various lengths and speeds of throw of the same valve are secured with various periods of admission, expansion, and release of steam. Link motions are thus of two classes: 1, the stationary link with shifting block; 2, the shifting link with stationary block. With these the results attained slightly differ; and beside, the principle, application, and effects of the link motion are capable of very great variation. Usual dimensions are, to give to the valve a lap of 1 inch, lead inch; the throw of each eccentric, 43 inches; length of eccentric rod, 54 inches; length of the link between attachments of these rods, 12 inches; with dimensions of the subsidiary links and levers in the proportions required. Then, certain main positions of the link and valve rod, as secured by the reversing lever, are as follows:

fore and back gear, and for forward and back strokes, may be had. This the shifting link fails to give; the lead here varies with the expansion, being least in full gear, and a maximum in mid-gear; but it may be made the same for the forward and back strokes. An admission through .75 stroke, is attended with a mean expansion of 16 per cent., with release at .91 of stroke; while .50 admission gives about .30 expansion, exhausting at .80= stroke. The least attainable percentage of admission, with the different forms of link, varies from .11 to.17 of stroke.-If, in an engine working under a given set of conditions, including a given action of valve gear, the boiler cease to supply the number of cylinderfuls of steam required at the velocity, the pressure on the piston and the speed proportionally fall; or if the ascent of grade increase, the resistance and work being greater, the piston cannot advance so rapidly, and the speed again falls, unless the power of the boiler suffice to raise the tension of the steam. On the other hand, if while the grade remains the same the steam pressure rises, or the pressure the same the grade diminishes, the engine runs faster, and until the increasing resistance mounts to an equilibrium with the power. Thus the true measure and limit of power of the locomotive engine are in the evaporative power of the boiler. But the calculations of power and speed belong to the subject and works of railway practice. The following table presents some examples of the tractive resistance per ton gross of engine, tender, and train on a level:

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-Since about the year 1830, and until within a few years past, the rapid improvement and introduction of railway locomotion had quite absorbed the attention of inventors, and the problem of steam carriage on common roads was comparatively neglected. The difficulties in the way of such propulsion of vehicles, moreover, remain considerable. In the great exhibition of 1851 there was but one locomotive for common roads exhibited; but since that time, in England, no fewer than 9 varieties of such engines have attracted attention, some of which have been employed for agricultural or for carrying purposes, and perhaps the most successful of which are the traction engines of Bray and Boydell. Among those interested in the subject in the United States, Mr. J. K. Fisher has thus far been the most successful. He built in New York in 1852 a small experimental steam carriage, with easy springs. This, on the Broadway pavement, in night With the stationary link a constant lead, through trials, outran horses; but it had not steam

Positions.

Full gear forward

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Mid-gear..

Full gear backward.

Eccentric
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Length of travel
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the season, at an average of 7 miles an hour, did not still lead to the general introduction of steam propulsion; though this clearsighted pioneer predicted the navigation by such means not only of the western waters of America, but also of the Atlantic ocean. Thus, the actual moving of boats by steam certainly occurred in this country, and perhaps in France, before the trials of Miller and others in Scotland, on which latter, however, the English endeavor to found their claim to priority. Patrick Miller and William Symington, in 1788, propelled on Dalswinton loch twin or double pleasure boats, by means of a paddle wheel placed between them, and by an engine with a 4-inch cylinder, attaining 5 miles an hour. With a larger engine, in 1789, they navigated the Forth and Clyde canal, at a rate of 6 to 7 miles an hour; but owing to insufficiency in the machinery, they were compelled to abandon further attempts. In 1796 John Fitch moved a small boat on the Collect pond, in the city of New York, by a small engine and a worm or propellor screw projecting from the stern of the boat; this being, probably, the first employment of the screw for propulsion. In the same year a work was published in Florence, claiming that an Italian, Serapino Serrati, had successfully propelled a boat by steam on the Arno; if this be true, still no further practical result followed upon it in that quarter. Meanwhile, Robert Fulton was in England and in France, and, if not previously interested in steam propulsion, became so upon inspection of Dr. Cartwright's steam barge, and Earl Stanhope's boat with duckfeet paddles under the quarters, neither of which however proved successful. In 1798 the legislature of New York granted to Chancellor R. R. Livingston of that state, who had been experimenting with steam for boats, the right to navigate the waters of the state by steam for 20 years; and though he failed to satisfy the condition of the grant by propelling a boat 4 miles per hour within the year, the grant was in 1803 renewed, and the time of fulfilment extended to 1805, and afterward to 1807. In 1801 Mr. Symington completed for Lord Dundas a steamboat, the Charlotte Dundas, its engine having a horizontal cylinder of 22 inches diameter and 4 feet stroke; this made, with boats to 140 tons burden in tow, on the Forth and Clyde canal, 3 miles per hour; but a prejudice excited by its washing the banks of the canal compelled its abandonment. About 1799, Mr. Livingston meeting with Fulton in Paris, they became together interested in projects for steam propulsion, and, notwithstanding the jealousy of Des Blancs, made at least two experiments on the Seine previous to 1804, neither of which succeeded. The breaking in the middle and sinking of their boat in the first instance by the weight of the engine, is believed to have led to Fulton's subsequent introduction of the strong and light framing intended to uphold the weight of large engines,

enough for common roads. He has now (1862) nearly completed a large carriage; and four self-propelling fire engines of Messrs. Lee and Larned's patent (see FIRE ENGINE) have been built, so far as their locomotive apparatus is concerned, on his plan. These all have springs of great flexibility, and yet run as steadily as ordinary carriages. This result is attained by using radius rods to hold the driving axle at a constant distance from the engine shaft, which revolves in fixed bearings in the main frame, allowing the axle to swing or to rise and fall, parallel rods being introduced to transmit the power. The parallel and radius rods terminate in ball and socket joints; and the lateral swing is limited by a transverse radius rod held by a spring. By these several methods, not only are the necessary lateral movement and flexure due to roughness of roads allowed, but also the rolling or oscillation of the carriage, without twist of the frame, or interfering with the accurate transmission of the power to the driving wheels. Of the steam fire engines, the cylinders are of 7 inches diameter and 14 inches stroke; the valves operated by a stationary link with reversing lever, and securing expansion in any desired degree. The power is derived from Lee and Larned's annular steam boiler. The speed of steam carriages on good common roads has been made to reach 30 miles per hour for short distances, and for journeys of three miles 20 miles per hour.-STEAM NAVIGATION. Paddle wheels, propelled by windlasses turned by men, or by animal power, were to some extent in use in the war galleys of the ancient Egyptians and Romans; it is uncertain whether they afforded any essential advantage over the use of oars. Even if Blasco de Garay, mentioned in treating of the steam engine, accomplished what has been claimed, the entire abandonment of his project shows that it must have been unsatisfactory; so that he can in no way be regarded as the originator of steam navigation. The attempts made in England and France, prior to 1730, led to no result. Jonathan Hulls in 1736 described a method of propulsion by a stern wheel acted upon by an atmospheric engine; but he is not known to have put his plan in practice. In France, from 1774 to 1796, the count d'Auxiron, the brothers Périer, the marquis de Jouffroy, and M. des Blancs severally constructed and tried boats to be propelled by steam, none of which were successfal. In 1786 John Fitch, of Pennsylvania, propelled by a very small engine, cylinder one inch in diameter, a skiff at fair speed; and in the same year, by a 12-inch cylinder, a boat on the Delaware, the speed however being in this case very slow. In 1787 Rumsey, of Virginia, attained a speed of at least 3 miles an hour on the Potomac, by reaction of water taken in at the bow of his boat by a steam engine and forced out at the stern; he tried this plan in England in 1793, making 4 miles an hour. Fitch's boat of larger size, placed on the Delaware in 1790, and making regular trips through VOL. XV.-5

which is one of the characteristic excellences of American steamboats. It was in 1804 that Oliver Evans, at Philadelphia, propelled his steam dredging machine, the Oructor Amphibolis, upon wheels on land, and subsequently by a paddle wheel upon the water. In the same year John Stevens, of Hoboken, N. J., propelled in the waters about New York a small boat by means of an engine, the steam for which was furnished by a very small tubular boiler, the power being applied by means of a form of screw also invented by him, and substantially that most approved at the present day. Fulton, meanwhile, had again visited England and Scotland, inspecting in the latter country one of Symington's later boats, and receiving from him information respecting its construction and working. Returning to New York in 1806, he commenced at once building, in conjunction with Mr. Livingston, a steamboat for use upon the Hudson. This boat, the Clermont, was of 160 tons burden, 130 ft. long, 18 ft. wide, and 7 ft. deep. She was provided with an engine from the establishment of Boulton and Watt, with a single cylinder 2 ft. in diameter and of 4 ft. stroke; boiler 20 ft. long, 7 ft. deep, and 8 ft. broad. The diameter of the paddle wheels was 15 ft., the boards 4 ft. long, and dipping 2 ft. in the water. On the morning of Aug. 7, 1807, Fulton with a few friends and mechanics, and 6 passengers, and leaving on the shore an incredulous and jeering crowd, started for Albany. The distance, 150 miles, he made at a speed of nearly, and on his return of full, 5 miles an hour. As the speed was still less than had been anticipated, the boat was lengthened to 140 ft. keel, and, being otherwise altered, was early in the year 1808 placed for regular trips on the Hudson between the cities already named. By tracing thus far the history of steam propulsion on water, we find that Fulton cannot be said to have been the originator of steam navigation, nor indeed the inventor of mechanism for such navigation; but the credit belonging to Fulton is that of having been the first successfully to cross the chasm from mere attempts to positive achievement-the man through whose energy and skill was first secured that combination of means which rendered navigation by steam at once practicable and profitable. Very properly, therefore, do the committee of the first London exhibition, 1851, say: Many persons, in various countries, claim the honor of having first invented small boats propelled by steam; but it is to the undaunted perseverance and exertions of the American Fulton that is due the everlasting honor of having produced this revolution, both in naval architecture and navigation." Within a brief period after the first trip of the Clermont, Mr. Stevens launched his boat, the Phoenix; but as Fulton's success had secured the right to navigation of the waters of New York, R. L. Stevens, son of the former, boldly took this boat round to Philadelphia by sea, this being indisputably the first instance of

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ocean steam navigation. (See STEVENS.) He also greatly improved the speed of his boats, attaining in 1814 to 13 miles an hour. In 1812 the first regular passenger steamer in Britain, the Comet, built for Henry Bell, appeared on the waters of the Clyde. This vessel was of 40 ft. keel, 10 ft. beam, 25 tons burden, and 3 horse power; her speed was 5 miles an hour. In 1814 Boulton and Watt first applied two condensing engines, connected with the shaft by cranks placed on it at right angles, in a steamer to run upon the Clyde. This plan has since become for boats of larger size a very general one. In 1818 the Savannah, a New York built ship, with side wheels, and propelled by steam and sails, crossed the Atlantic to St. Petersburg via Liverpool, reaching the latter place direct from New York in 26 days, and returning in safety. Although this was the first crossing of the Atlantic by steam, yet as the ship had but small engines, and was unsuited to the risks of such a voyage, the event scarcely demonstrated the practicability of ocean steam navigation. The first regular passages were made by the Sirius and Great Western in 1838, the former making the trip from London to New York in 17 days, and the latter from Bristol to New York in 15 days. In 1811 Fulton and Livingston established a ship yard at Pittsburg, and built an experimental boat, the Orleans, the first ever placed on our western waters. This boat had stern wheel and masts; her first trip from Pittsburg to New Orleans was made in the winter of 1812. This seems to have been the first successful application of the stern wheel, now in very general use on the western rivers, especially for boats of light draught. (See also SHIP.) Of the best class of American river steamers, a good example is the New World, built in 1847, of 1,400 tons, and placed on the Hudson between New York and Albany. Her engines were built by the firm of T. F. Secor and co., condensing, of 76 inches diameter and 15 ft. stroke, provided with double balance valves and Stevens's cut-off, worked by the usual eccentrics, lifter rods, and rock shafts with their levers; the two boilers being circular, and with single return flues. Of this boat the length is 375 ft.; breadth, 36 ft., over guards 69 ft.; depth of hold, 10 ft. 6 in.; the average speed of run, landings not included, is 18 miles per hour. The steamers City of Boston and City of New York, running on Long Island sound, embody a more recent style, in some respects, of construction and of propelling machinery; their engines are from the Novelty iron works, New York, hull by Sneeden and co. The Daniel Drew, running upon the Hudson, has recently made, on a trial trip, a speed of 22 miles per hour. The successful introduction of the screw was through the experiments of Capt. Ericsson and F. P. Smith, on the Thames, in 1837. The speed attained, with a large ship in tow, and against tide, was 43 knots an hour. The next screw vessel, the Robert Stockton,

built in 1839 for an American gentleman, was also successful; while the success of the Archimedes, in 1840, of 232 tons and 80 horse power, was so great as to attract the attention of the English admiralty; and from this time the screw advanced rapidly into favor, employed either as sole or as auxiliary means of propulsion for men-of-war or fast-sailing merchant vessels. Many peculiarities in the construction of marine engines, their accessories, working, and forms of boilers, have already been mentioned in treating of the steam engine. To combine the three things requisite in a steam vessel, the ship, the engines and boilers, and the wheels or other propeller, each of which is in itself a complex study, is one of the most difficult problems of modern engineering, demanding in the highest degree theoretical attainments and practical skill. The marine steam engine is necessarily made as light, compact, and at the same time as economical of fuel as possible. One of its oldest varieties, the side lever form, is still in use in some of the largest paddle steamers, among them those of the Cunard line. Although it has many advantages, yet, in view of the value of space and weight in merchant and passenger steamers, it is probable that the lighter and more compact direct-acting forms of engine, though more expensive in working, are in the total more economical. The screw propeller, or screw, which is the means of propulsion in those vessels named from this circumstance screw steamers or propellers, consists in its simplest form of a very strong metallic plate, standing edgewise on a cylinder or shaft, and winding round it like the blade of an auger, or of two or more blades or vanes, forming parts of such spirals. The shaft is made very strong, continued within the hold of the ship, and intended to revolve. The screw or blades are upon that part of it projecting from the stern of the ship, and space for the turning of the blades is allowed by a vertical oblong recess in the keel and stern, just before the rudder. The position of the shaft is such that the screw shall usually be wholly submerged; and upon the portion of the shaft within the hold one or more engines are made to act, either by cranks formed on the shaft, or by means of geared wheels. The use of such wheels admits of a slow speed of piston with a high speed of the screw; while on the other hand these wheels are necessarily cumbrous, their wooden teeth are liable to be "stripped" or broken off by a sudden stroke of the sea upon the screw, and they are unavoidably attended with a loud and disagreeable rumbling noise. Vessels of considerable draught admit of a diameter and pitch of screw sufficient for propulsion, without undue speed of the piston and without gearing. In the best marine engines the deduction for friction, the working of valves, pumps, &c., from the indicated or gross horse power, in order to find the effective or available propulsive power, may be taken as usually about 25 per cent. To increase the linear

advance of a screw against the water, which corresponds with a given rate of turn called the "pitch," the number of revolutions of the screw must be increased; and as the pitch best for effect is limited by the diameter of the screw, and this by the draught, and as for each revolution of the screw two journeys of the piston are allowed, the time, and hence the stroke, is necessarily short; the disadvantages are, the more frequent recurrence of the dead points, a proportionately greater loss of steam in filling the passages to the cylinder, and a narrower limit to the employment of expansive working. Still in most marine engines, whether for paddles or screws, steam is worked expansively, though seldom to the same extent as in land engines; the best results being secured when the cylinder is surrounded both with jacket and clothing, or the steam sufficiently superheated. In respect to the necessity of preventing accumulation of saline matters in the boilers of sea-going vessels, with consequent raising of the boiling point and tendency to scale within the boilers, it is now the usual practice to blow off the requisite quantity of brine continuously, and from the surface as well as the bottom of the boiler, in due proportion to the quantity of feed water admitted, so as to keep the water at that degree of saturation found by experience to be attended with little or no deposit. The density of the brine is known either by the hydrometer, or by instruments for the purpose termed salinometers. One of the most dangerous and troublesome tendencies of a boiler is that known as priming, as, beside the great loss of heat and of steam pressure occasioned by it, it may also cause the breaking down of the engine by the shock of the piston on the incompressible fluid in the cylinder. Remedies resorted to are, the increase of size of the steam chest, increased height of the steam pipe orifice above the surface of the water, and sometimes the adding of tallow to the water in the boiler. By the throttle-valve of marine engines, the flow of steam to the engines is usually regulated or shut off by hand. The ordinary vertical form of governor is of course wholly inapplicable, through the pitching and rolling to which the ship is liable. But in a heavy sea, one wheel or the screw being sometimes lifted quite out of the water, the engine begins to "race," i. e., to fly off at very high velocity, the liability to this result being greater with screw than with paddle steamers; and in such case an automatic and prompt-acting substitute for the hand becomes very desirable. The desideratum in these cases has recently been supplied by 3 or 4 different contrivances. The earliest of these were Silver's "momentum-wheel governor," and his "four-ball" or "balanced governor ;" these instruments act equally well in any position. The same result is secured in a more recent invention, Porter's "marine governor," with suspended and balanced balls, acting by compression, according to speed, of a spiral spring. In

all these forms it is true that the remedy must be applied after the evil has begun to develop itself. Jensen, of Copenhagen, has accordingly attempted to produce a prompt and perfect marine governor, by admitting the water of the sea to rise in two small cylinders directly through the bottom of the vessel, and as near as may be to the screw or wheels; pistons moving on and with the water in these cylinders, are made by levers to control the steam valves; and thus the irregular immersion of the vessel itself is caused to regulate the supply of steam to the engines.-Paddle wheels are generally of two kinds, those with common or fixed, and those with feathering floats. Wheels with fixed floats, when a vessel is anchored or is yet moving slowly, act at great disadvantage; since those entering the water strike it obliquely, and waste much of the power in a tendency to lift the bow of the vessel, instead of propelling it, and those leaving the water lift much dead weight in the form of back water. But when the vessel has acquired fair or rapid speed, its very motion largely overcomes these difficulties, and the dip of each float into the water, and its withdrawal out of it, virtually occur nearly edgewise, the effect being similar to the "feathering" of an oar by the rower. But with a paddle wheel badly proportioned, immersed too deeply in the water, or attached to a slow boat, the unfavorable action above referred to is largely experienced. By making the floats movable about horizontal axes through the middle, and controlling their position by a second wheel, set eccentrically to the paddle wheel, as well as in other ways, they are made to feather on entering and leaving the water. By such arrangement the speed has been increased, and the vibration due to the movement of the wheels greatly reduced. The excess of the velocity of the wheel above that of the vessel, called the slip, is in favorable circumstances about the speed of the latter; feathering wheels have less slip. As, in the screw, one, two, or three threads are readily placed within the distance of a single coil, we have thus single-threaded screws, double-threaded, and so on. The distance to which the screw would enter a solid during a single revolution, is of course the distance or length of one complete turn; and this is the measure already named the pitch of the screw. But since, worked in water, the medium gives way in part before it, the screw does not advance the full amount of its pitch, and this deficiency is called the slip of the screw. Supposing the screw cut into portions by planes at right angles to its axis, these would be the vanes or blades; and according as the screw was two-threaded or three-threaded, two or three of these would stand opposite each other. This form, in which each blade is but a small portion of the complete pitch, is that now commonly in use. What is called negative slip in propeller screws, is that result in which, owing to the drawing by the ship of a wake or

current after it, the screw acting in this current causes the vessel to advance faster than the blades of the screw at the same moment are entering the water or would enter a solid surrounding them. Owing to the current, however, the real slip is not apparent. In reference to the comparative value for propulsion of paddle wheels and screws, it may be said that when both are in their best trim, and well proportioned to the vessels and the engines, they are about equally efficient. The screw, however, in ordinary weather, is apt to have a more uniform immersion and action; while a great disadvantage of its use is the increased speed which must be given to the engines.

STEARIC ACID (Gr. σreap, tallow), a fatty acid obtained from mutton suet, and other fats that contain stearine, by the process described in CANDLE, vol. iv. p. 355; symbol, HO,Cs6 HзO3. When recrystallized from ether, until the fusing point becomes constant at 159°, and slowly cooled, the acid forms beautiful, colorless, transparent, rhombic plates; these melt into a colorless oil, tasteless and without odor, and when quickly cooled the substance concretes in a white crystalline mass, which is insoluble in water, but readily forms with hot alcohol a solution having acid reaction. It is the material of the so called stearine candles. Stearic acid exists in fats in combination with glycerine, forming stearine, from which it is separated by saponification. (See GLYCERINE.) It combines with numerous bases, and forms with them both acid and neutral salts, called stearates. Stearate of soda is the basis of ordinary hard soap; stearate of lead is one of the constituents of the common lead plaster.

STEARNS, a central co. of Minnesota, bounded E. by the Mississippi, and drained by Sauk river and lake; area, 1,379 sq. m.; pop. in 1860, 4,505. A portion of the county is prairie, but the W. part is mountainous. There are numerous lakes and streams. Capital, St. Cloud.

STEATITE, or SOAPSTONE, a compact variety of the mineral species talc, consisting of silica 62.14, magnesia 32.92, and water 4.94 per cent., being a hydrous silicate of magnesia. It occurs in massive beds among the metamorphic rocks, often associated with serpentine. The stone is distinguished by its soft and uniform texture, which admits of its being cut by the knife or saw, especially when freshly quarried, and also by its property of withstanding intense heat. Its colors are coarse gray and grayish green, sometimes yellowish; the texture generally granular; lustre dull; specific gravity 2.65 to 2.8; structure compact, sometimes lamellar; and to the touch it is greasy like soap. When crystalline or in thin and flexible folia of pearly lustre, it is commonly known as talc, of which the substance employed under the name of French chalk for removing grease spots is a variety. Meerschaum is another variety. The uses of soapstone are numerous, and beds of it furnishing large blocks unmixed with other substances are val

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