other arrangement employed on any Corliss engine in use at the present day.

Some of the most important features of the Reynolds Corliss Engine are that they are stronger and heavier than most engines of that class; that the valves are under the complete control of the governor, which is very powerful and sensitive, thus insuring uniformity in speed, which is a feature of great importance for milling and most other manufacturing purposes; that the valvegear is simple and conveniently arranged for accurate adjustment; that the fly-wheel is turned on the face and sides and accurately balanced; that the wearing surfaces, whether revolving or rubbing, are ample, which prevents the possibility of rapid wear and the expense of repairs; and that the cross-head pin, crank-pin, and piston-rod are made of steel, and the crank-shafts of the best hammered iron.

The Reynolds Corliss engines are in very general use, and have a well-earned reputation for durability, efficiency, and economy. The condenser and air-pump are new in design, simple, and efficient; in fact, the whole design and arrangement of these engines show them to be the result of mature mechanical deliberation. They are manufactured, both condensing and non-condensing, simple and compound, of any size and power, to meet the requirements of purchasers, by Edward P. Allis & Co., Milwaukee, Wis.

Steam- and Exhaust-Pipes.

The diameter of the steam-pipe varies with leading engine builders between and the diameter of the cylinder, the exhaustpipes being from about 30 to 50 per cent. larger. Some builders make them little, if any, larger; but too small steam- and exhaustpipes are a prevailing vice amongst small builders, especially those in country districts, who do not use an indicator to determine their proportions. The proper diameter for steam- and exhaustpipes may be found by multiplying the diameter of the piston in inches by its speed in feet per minute, and dividing the product

by 1440 for steam- and 1140 for exhaust-pipes; the quotient will be the diameter of the pipes in inches. For short and direct pipes, however, the divisor may be increased to 2000 for steamand 1440 for exhaust-pipes. These latter divisors will give proportions a trifle larger than the average, especially for exhaust.

Rock-Shafts.

Some engine builders make the diameter of the rock-shaft the diameter of the crank-shaft; if subjected to torsion, it should be, and in some cases, the diameter. The torsion on a shaft is in proportion to the length of the arm to which the valve is attached. About 10 times the area of the slide-valve in square inches will nearly equal the force in pounds required to move it under 100 pounds steam pressure, though, when dry or starting, it may amount to 12 times or more. The diameter of a rock-shaft may be found by the following rule. Multiply the maximum resistance in pounds by the length of the arm which divides the valve, and divide the product by 128; the cube root of the quotient will be the diameter of the shaft in inches. The size thus found will answer for ordinary wrought-iron shafts, and will resist greater strain than the above rule provides for. The rocker and rock-shaft are being fast superseded by the guide-block.

Cross-Head Bearings.

The area of the wearing surface of a cross-head (that is to say, the total, above and below) should not be less than the area of the piston, nor ever exceed of it. Many steam-engine builders make the length of the cross-head bearings the diameter of the cylinder, and their width of the same, which appears to be a good proportion, and may be illustrated as follows: of a 12 in. cylinder is 8 inches in length, and is 2 inches in width, which gives 20 sq. inches for each shoe, or 40 for both, which is a good proportion; but it should be slightly greater in the case of

short connected engines running at a high speed. The cross-head gibs are generally termed shoes, and the grooves in which they move are called V's.

Valve-Rods.

The diameter of valve-rods varies for moderate sized engines from to the diameter of the cylinder. Their diameter in any case should be proportioned to the size of the valve, whether it is balanced or not. If the area of the valve be considered as a piston of such area, its diameter will bear about the same relation to its maximum strain as piston-rods do; but valve-rods are generally made somewhat larger than such a rule would give, because they are not so well protected against side strains as piston-rods. Probably, since the area of a piston-rod should be from 3 to the area of the piston, according to its length and material (steel may be smallest), a valve-rod should be about from 30 to 30 of the unbalanced area of the valve for high-pressure engines.

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The Eccentric.

The eccentric.-An eccentric is substantially a crank, with its pin enlarged in diameter so as to inclose the shaft on which it is placed within its periphery. It gives exactly the same motion that would be obtained from an ordinary crank of equal throw. The eccentric is sometimes called a cam, which is erroneous, as the latter is always used to obtain a motion different from what can be obtained from a crank. The term "cam," when used without qualification, is indefinite, and conveys no impression of its precise form or functions. It is a mechanical element of such a form that a solid body held against, but not revolving with, the periphery of contact may have an intermittent, alternating motion.

Fore eccentric. - A "term" applied to the eccentric, which is connected by its rod to the upper part of the link, to move the valve for the forward motion; but the reason that the forward motion is derived from the upper end of the link arises from

convenience, and not from necessity. The reverse conditions could be introduced very easily.

Back eccentric.- -The eccentric connected to the lower end of the link by which the valves are adjusted for the backward motion. Throw of the eccentric.-The "term" throw of the eccentric is understood to be the same as the travel it imparts to the valve, and which is understood to be equal to the width of both steamports with the lap added.

Angular advance of the eccentric means the angle at which it stands in advance of that which it would occupy if the valve were in the centre of its travel, and the crank at its centre.

The Crank.

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The generally prevalent idea among mechanics that there is an actual loss of power in the use of the crank, has stimulated inventors to substitute for it a device that would utilize all the power exerted against the piston without loss. As a result, the U.S. Patent-Office, as well as those of the different countries of Europe, are crowded with arrangements intended to supersede the crank; the most popular, and conse-180 quently the most frequently resorted to, being the rotary engine, in which the effective force of the steam would be constant, while in the case of the crank it is intermittent;

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but, so far, no rotary arrangement has ever been able to compete, in point of economy, with the reciprocating motion of the crank. Strictly speaking, there is no loss of power in the use of the crank, as, while there is a great variation in the power a given

pressure of steam can exert at different points of the stroke, it is known that when the power is least the consumption of steam is least. Suppose an engine has 2-feet stroke, the piston would travel 4 feet for each revolution; during each stroke the effective length of the crank varies from 0 to 1 foot; its average effective length would be equal to the radius of a circle whose circumference was 4 feet, or 7.68 inches. The power of the engine would be the same as if it acted on a constant crank of 7·68 inches, and the displacement, and consequently the consumption of steam, would be the same as before.

If the piston acted on a constant or average crank of 12 inches in length, it must travel a distance equal to the circumference of a 24-inch circle, or 633 inches. Though such an engine would have proportionately more power at the same number of revolutions, it would consume proportionately more steam. The power of a crank is greatest for early cut-offs at the point at which the valve closes, and for late cut-offs when it stands at right angles with the connecting-rod, which point, as may be seen from the cut on page 175, is not in the middle of the stroke.

An examination of the connecting-rod of an engine in motion, will show that the two ends pass over different spaces in a given time. If, for instance, in one stroke the end of the connectingrod that is attached to the cross-head moves through one foot, the end which is attached to the crank-pin, and makes a half revolution in the same time, passes through 1.5708 feet. Suppose that an engine is placed with its crank on the centre, and steam is admitted; no motion will be produced, and consequently there will be no power developed, and no expenditure of steam; but let the piston make a stroke, the power exerted is equal to the force or pressure acting on the piston multiplied by the space passed through, or it will be 100 foot-pounds, assuming the data previously given. During the same time the crank-pin has passed through a space of 1.5708 feet, and the force or pressure exerted has been 63-66 pounds, so that the power exerted during this time, or the product of 1.5708 multiplied by 63-66, is 100 foot pounds.