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facility to the fluctuating demands of the engines, when alternately starting and stopping at short intervals. This ability to hold steam is a most im- portant feature when a steamboat is maneuvering in a narrow channel, or making a landing, as the situations are often critical and frequently require a full head of steam without an in- stant's delay. ues Another feature which _ especially adapts them to service in a steamboat is their remarkably light weight. The steam pressure carried varies from 165 to 185 pounds, but their small diame- ter, rarely exceeding 36 in., permits using very thin boiler plates, and the absence of combustion chambers, stay-rods and boilen tubes results in an enormous decrease in weight over that which would ordinarily be found in other steam-producing apparatus of the same power. But what is particularly advan- tageous to the frail hull of a steam- boat, is that the weight, instead of being concentrated, is distributed over a considerable distance fore and aft. When one considers the great dis- parity between the weight boilers above and the buoyant force immediately beneath, resulting in the production of enormous local stresses whijch_the shallow hull is ill adapted to resist, it will be seen what great importance attaches to this fact. Some kind of mechanical draft is hecessary in order that the size of the boilen plant may be as small as possible, in proportion to the power of the engines. The construction of the furnaces and the open, exposed character of the fire room is unsuita- ble to the use of forced draft. sequently induced draught is used ex- clusively, either taking the form of directing the exhaust steam from the engines into the smoke stacks and thereby creating a partial vacuum, or else fitting separate blowers in the uptakes. The former is objectionable on account of the resulting tremen- dous noise which resembles the roar- ing of a volcano, so that the latter is more often found on passenger boats of the better class. Western river steamboats, whether of the side or sternwheel type, are invariably fitted with two distinct and separate sets of engines. This ar- rangement is obviously necessary in the case of the latter, but it is de- sirable in the former also, on ac- count of the ability to operate the side wheels independently, which it permits. inclined or horizontal type, and are usually simple expansion. Compound of the, . ious Con- . These engines are of the "TAE MARINE REVIEW. engines when adopted at all, have been exclusively applied to stern- wheel steamers, where the high and low pressure cylinders have been ar- ranged tandem, both pistons operat- ing on one rod, which is directly con- nected to the ponderous pitman. Condensers are rarely used, the exhaust steam being generally al- lowed to escape directly into the at- mosphere, or directed into the smoke stacks, in order to increase. the draft to the furnaces. However, a number of boats have recently been equipped with condensers of the jet type. No attempt is made to use the condensed steam for boiler feed; the condenser being intended merely fon the purpose of giving the engines the benefit of the vacuum which they provide. Valve gears, auxiliaries, and other appurtenances of this type of engine differ entirely from those to which the marine engineer is accustomed, but they cannot be described very well without greater elaboration than the length of this article will permit. Suffice it- to say that they are ad- mirably adapted to the engine in its present form. but in action are heter- odox in respect to all accepted tradi- tions of the deep sea engineer. But there is one feature of the steamboat which cannot fail to at- tract attention, and that is, the ingen- instrument which converts the power of the engines into propel- ing force. The tremendous cataracts of yellow water which they raise, and the enormous swells which result, are the familiar sights which accompany the passing of a river steamer. dle wheels of the radial type have, so far, been used to the exclusion of every other form of propeller. The reason for this lies in the fact that paddle wheels possess an_ essential quality which is of paramount im- portance to a steamboat, and that is, equal efficiency in backing and going ahead. Without it no form of pro- peller can be of much service to a steamboat which is entirely dependent on this feature in maintaining its self- control, Feathering paddle wheels have not been experimented with as yet, on account of the danger to their mech- anism from heavy drift, but an at- tempt-has been made in some stern- wheelers to reduce vibration by set- ting the floats on one-half of the wheel, some distance ahead of those on the other half. This arrangement has been attended with a good deal of success, but of course does not re- Pad- -- 29 sult in any increase in propulsive efficiency. The entire wheel, floats, rim, and arms, is constructed of wood, so that any damage can be quickly and cheaply repaired. This question of damage is an important consideration, especially to the floats, which are continually striking logs, smashing into the willows, and otherwise in- juring themselves. The shaft is us- ually of hammered scrap iron, though in one or two exceptional cases nickel steel has' been used. A _ prominent steamboat man has stated that nickel steel shatts, even when complying with the most rigid specifications have repeatedly failed, and that wrought iron seems to be the only reliable material adapted to the inter- mittent shocks which these shafts experience. The steamboat must be under com- plete and perfect control at-all times. -- If this were not so, they would be unable to navigate successfully in the swift current of the western rivers. Running unden numerous bridges with narrow channel spans, and with treacherous cross currents constantly tending to swerve the boat from its . course; effecting a multitude of land- ings in close and restricted quarters where stumps, branches. wrecks and other obstructions threaten to tear the boat's timbers asunder; and al- ways borne on the surface of a rapid current, which renders steering a dif- cult matter, are conditions which constantly demand an unusual de- gree of steerability. On account of the light draught it is impossible to-provide this qual- ity in stern-wheel boats without fit- ting several rudders instead of one. These are of the balanced type, and usually four in number, all hung in a row on the transom, forward of the wheel, and connected by a yoke to two tillers which operate together. In recent years a steam steering ap- paratus has been 'adopted on most steamboats, which consists simply of a steam cylinder placed athwartships underneath the boiler deck, with the piston rod connected through a mov- able arm to the tillers. Steam is admitted to either end of the cylin- der by means of a valve which is operated through a system of rope leads by the steering wheel in the pilot house. In laten styles of this apparatus the pilot does not work the steering wheel, but operates a lever placed immediately behind it. The whole arrangement is unusually simple and free from all complexity and hence is seldom out of order.