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WHERE THE BATTLE OF BULL RUN BEGAN. “Run " is the Southern term for “creek." This bridge marks where the Warrenton turnpike the war-worn road across northern Virginia between the Potomac and the Rappahannock — crosses the stream. Here began the sanguinary battle of July 21, 1861, Tyler's division of McDowell's Union army being on the right (east side) of the picture, and on the west or left-hand side Evans's brigade of the Confederate army under Beauregard. There was fighting in the neighborhood of the bridge in 1862 also, and a man standing on this old bridge could have heard the guns of a score of fights in the Civil War.

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SHROUDED IN CIVIL WAR MEMORIES. The old McDowell house at Centerville, Fairfax County, Virginia. It faces westward toward the battlefield of Bull Run three miles away. Here Gen. Irving McDowell had his headquarters, and from this house marched to the fight. Four miles to the rear is the field of Chantilly, where Gen. Phil Kearney was killed; and a few miles north lies Aldie, of Civil War memory. The house several times sheltered the wounded of both armies during the long struggle,

ICHALK

TALKS

by CARL S. DOW.

Number Thirty-Three-Blower System of

Heating

OOMS are warmed to a comfort- ting heat in steam pipes than in large
able temperature by conveying ducts or flues.
to them an amount of heat suffi In the indirect system as installed in

cient to make up for the loss re- small buildings, the air flows to the rooms sulting from radiation through walls and because of natural circulation. The windows, the leaking of air around doors, warm air in the room leaks outward, and windows, etc. The two most successful the heated air rises from the basement to mediums are steam and hot water, for take its place. these readily absorb heat and as readily give it up to the surrounding air and ob

Fan Systems jects.

In large buildings it is often necessary

to supply air in large quantities for ventiDirect and Indirect Systems

lation. This is especially true of buildBoth mediums are applied in systems, ings of a public character, such as known as "direct” and “indirect." In the churches, schoolhouses, theaters, etc., for former, the pipes or radiators through in these structures many people are conwhich steam or hot water flows are placed tained in comparatively small space. In in the room to be heated, and the heat such cases, the natural circulation of air is supplied from them by direct radiation. in the indirect system will not supply a In the indirect, the coil or radiator is lo sufficient quantity, and the direct system cated in the basement, or at the base of is useless for ventilation. To get the rethe flues leading into the room, and the quired air, it must be circulated mechaniair passing over it takes up heat and car- cally, and this is best accomplished with ries it to the room. In some respects the some form of fan or blower. indirect system resembles furnace heating, for the hot air comes into the room

The Blower through registers, no heating apparatus This machine is simply a sheet-metal being in sight.

casing of scroll shape, within which a It is evident that the indirect system steel-plate fan wheel revolves at high is preferable to the direct as to ventila- speed, taking air at the center or shaft, tion, for no ventilation occurs with the and giving it rapid motion by means of latter installation. With the indirect, the revolving blades or vanes. Delivered considerable air is introduced in order to at the tips of the blades, the air leaves the supply the required amount of heat. The fan, under slight pressure, by a tangenefficiency of the direct system is, how- tial outlet. For heating work, the fan is ever, greater, for all the heat is supplied usually operated by a small steam engine, directly to the air and objects in the the set being called a "steam fan.” room, and there is less loss in transmit- There are two distinct methods of fan (342)

(Rights of publication reserved hy Author)

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heating. In one, the air is heated in the the pressure within the building is less basement to a high temperature (higher than that outside, and air leaks in from than that of the room). On entering the all sides. Evidently purer air will be room, the heated air supplies enough heat maintained in the Plenum, for it can be to replace that lost through walls and drawn from a reliable source. windows. By the other method, direct The sketch on the blackboard shows the genradiation (steam pipes or radiators in the eral arrangement of the apparatus used in the room) furnishes the required amount of Plenum system. Air from out of doors enheat, and a fan forces in air at the room

ters through an opening into the Plenum

chamber, in which a small heater, called the temperature, to provide ventilation.

“tempering coil,” heats it to about 70° F. It The first-mentioned method is better for is then drawn into the fan, which forces it buildings that must be kept warm all the time; among and between the pipes of the main it has the advantage of requiring the installa- heater. As it is under slight pressure when tion of but one system. The second is often it leaves the coils, the air passes up through selected for buildings to be ventilated but a the ducts to the rooms above. The apparatus few hours at a time; for the fan need not is provided with suitable dampers, by means operate except when the occupants are in the of which hot air, a mixture of the tempered building, and it is not necessary to supply more air and the heated air, or the tempered air air than that required for ventilation. But alone, may be directed to the rooms. two separate systems must be put in.

For warm weather, the air from outside

may be passed through the fan, and thence to Plenum and Exhaust Systems the rooms, without passing through the heater,

thus supplying frequent changes of air. The fan system may properly be divided into two classes, in the first of The blower system has the advantage which the rooms are under a slight pres- of being independent of the direction of sure; that is, the pressure within is just wind, positive in action, and economical enough to cause all leakage to be out as to cost of running the fan; for the exward. This is called the "Plenum." In haust steam from the engine may be used the second, called the “Exhaust” system, in the heater.

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Surf-Driven Motor THE illustration shows a motor driven 1 by the power the waves bear in their shoreward sweep. A sloping beach is necessary for the operation of the machine. Given surf and a favorable position on the shore line, the inventor believes his device should do excellent service. It is designed as follows:

A platform is constructed, with four standards, one at each corner. These standards support as many sheaves, over which two cables are passed. The cables are for the purpose of drawing the motor into or out of the water as may be de

passes over a series of pulleys, to one of which is attached a counterweight. The purpose of the counterweight is to take up slack when the motor is drawn in toward shore. One of the pulleys is fixed to a shaft; and this, in turn, is connected with additional apparatus, consisting of levers, drums, and other gear, all of which complete the chain and keep the motor in operation.

Wooden Clothes It will probably not be very long before

we can go into one of the dry-goods stores and say to a clerk, "Let me see

what you have in the line of wooden suits." He may reply, "Hard or soft?” whereupon it will be our part to specify that we want a suit of "good" pine, "without any cheap sapwood." Vests of this kind are already worn by the carding-room foremen in some of the woolen mills. The material resembles a stiff, thick cloth, and is apparently as durable as leather. It is not improbable that in

the future cheap suits, costing about 50 cents and guaranteed to last for years, will be made of spruce or pine. Napkins, shirts, collars of the finest quality, have long been made from the fiber of hemp ; and in using wood for heavier cloth, the process is equally simple. The wood is first ground into a soft pulp, and this pulp is pressed through holes in iron plates. It comes out in long ropes about 1/2 inch in di

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COURTESY OF SCIENTIFIC ANERICAN."

A SURF-ACTUATED MOTOR.

sired. This object is accomplished by the turning of a crank. A series of buckets attached to cables comprise the motor proper. As the buckets pass into the waves, they of course fill; and as they are drawn up by the cables, they are overturned and thus emptied of their contents. The motion thus set up is transmitted by cable to the machinery of a framework on shore. This cable

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