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on which the dam will move as it opens and closes.
Under this girder will be another girder, not quite so large, but still large enough not to be ashamed of itself. It will not weigh seventy-five tons, but it will weigh almost fifty-seven. It will lie on its side, instead of standing on its end.
Beneath this second girder there will be an enormous mass of concrete, buried
look like the skeleton of a big leaf, with the stem rising in the middle and seven slender, denuded ribs stretching stiffly out on either hand.
But the last part of the work is yet to be done. Big steel plates will be affixed to the ribs of the skeleton. Each wing will become practically a solid mass of steel. And each wing will be so securely attached to the central girder that the
GIRDER AS LOADED ON FLAT CARS, EN ROUTE TO LOCKPORT..
beneath the bed of the stream and assist whole dam will be practically one big ing the metal of the dam to withstand piece of metal. the push of the waters of the Drainage Between Chicago, therefore, and Joliet, Channel, the waters of the Chicago River which is the end of the Drainage Chanand the waters of Lake Michigan. nel, there will rise at Lockport this strong
At the bottom, then, the mass of con- steel barrier, reaching from bank to bank crete. Above it, the little-brother girder, of the Drainage Channel and restraining reposing on its side. Above that the all possible excessive ambitions on the big girder, standing upright and rising part of the waters of Lake Michigan. to the surface of the water. All these The top of the butterfly dam will rise in the center of the stream.
to exactly the same height above sea level On each side of the big girder, span- as the surface of the waters of Lake ning the distance between its huge bulk Michigan. Not one drop from the lake and the banks of the channel, will stretch will be able to flow to Joliet or to St. the wings.
Louis when the dam is closed. It is Each of these wings will have seven clear, therefore, that in a way the butterribs, seven ribs of steel. Each rib will fly dam will be the southwestern shore be ninety feet long. If the construction of Lake Michigan. It will represent the should stop at this point the dam would farthest southwestern reach of that lake
before it begins to take the rapid, pre- The danger is hypothetical, which, transcipitous descent which lies between the lated from the language of the engineers, butterfly dam and the city of Joliet. means you-don't-need-to-worry-about-it. The water lapping the top of the butter- But in order to guard against even a fly dam will stand at the same level as hypothetical danger the butterfly dam the water which lies at the edge of Grant has been called into existence. Park at the mouth of the Chicago River. It is the first time that the butterfly
Between the butterfly dam, near principle has been applied to an engineerLockport, and the City of Joliet there is ing undertaking of any magnitude. When a sudden drop in surface altitude. Be- the butterfly dam at Lockport has been cause of this drop the Drainage Channel swung across the stream the farms of is able to turn a large number of tur- Illinois may go on producing corn in bines and, in consequence, to produce a peace. The southwestern boundary of large number of kilowatts of electric Lake Michigan will hold back all the energy. Also, because of this drop, the water that has ever been discharged into Drainage Channel, between Lockport and that inland sea by the streams of MichiJoliet, ceases to run in a cañon, cut into gan, Indiana, Illinois, and Wisconsin. the solid earth, and begins to run be- And Chicago will have given the world tween enormous concrete walls, resting the first butterfly dam which has ever on the surface of the earth and confining been erected on a large scale. the flow of its waters to a kind of aërial But—and this is a “but” which exaqueduct, standing prominently above plains the adoption of the butterfly the surrounding country.
principle—the dam at Lockport will not If any part of these walls should ever usually be swung across the stream which give way—which is unlikely—the farms it is constructed to intercept. It will of the neighborhood would be flooded. usually lie parallel with the stream. The
ordinary attitude of this extraordinary Slowly, irresistibly, it swings back on dam will be that of a log lying length- its big metal pins. The rushing waters wise to the current.
of Lake Michigan are driven back beThere will be two metal pins in the fore it. It turns below water like any butterfly dam. One of them, weighing swing-bridge that turns in the air above. six tons, will traverse the central girder In the space of a few minutes the from the top. The other, weighing ten channel can be closed, the waters of the tons, will traverse it from the bottom. The central girder, with its seven rooms, is so constructed that the walls of these rooms are pierced with the holes through which these pins will be thrust.
Turning, slowly turning, on the sixteen tons of cold steel which form its spinal column, the butterfly dam swings from its occasional position athwart the stream, where it holds back Lake Michigan, and gradually approaches its normal, ordinary position, lying finally in the same direction with the current which it controls and allowing the severed portions of that current to flow by unchecked on either side of it. One wing of the dam now lies upstream. The other wing lies downstream. The appearance of the dam is now that of a barge
END VIEW OF CENTER GIRDER OF BUTTERFLY DAM. floating endwise down to Joliet. Now, just suppose that some
one little stretch lake hurled back, and disaster is averted. of one of the concrete walls of the The top of the dam is as high as the top channel below the dam has given of Lake Michigan. And water cannot flow way. Suppose—it is almost impossible, above its own level. The butterfly dam but-suppose that the waters of the swings shut and the fields of Will County Drainage Channel, with the whole pres
This is the use, this is •the sure of Lake Michigan behind them, are adaptability, of the butterfly dam. surging out over the crops of Will times of watery peace it lets the whole County. This dam has not broken. It body of the current go by. In times of has not given way. It has not yet been watery war it intercepts every drop. It used. It is still to be called into service. spreads its steely wings, or contracts It is the reserve force of the engineering them, in obedience to the welfare of army of the Sanitary District.
the state of Illinois.
HE oily face of the camp- "Why, there must be—there must be
satchel, smaller than any of the kinds “Gold!” he whispered. “It's full of usually used for carrying clothing, bound gold! Jim told me to tell you to take up tightly with a scarred strap that had care of it for him."
once been black, with a lock at the top "The deuce he did," muttered Carter. and fasteners at the sides, from which the He eyed the absurdly small leathern grip nickel-plate had been worn by long usage. which, on Bud's information, he had just It was not a pretty thing. In fact, it pulled out from under Jim Bell's bunk was a sufficiently disreputable looking in their miner's shack, and swore softly object to serve admirably as an entirely under his breath.
safe deposit receptacle for its fill of gold “Yes, he said they was gold in it," in- dust. sisted the boy, "and he told me to tell But Carter was puzzled. How in the you to take care of it for him. He said world Jim Bell has accumulated any it would be six weeks before he could such amount of dust as must be in that get back and he wouldn't trust nobody little grip without his, Dan Carter's,
knowledge, was a thing hard to fathom. Carter swore again, not so softly. Jim was his chum and they had been unThen he got to his feet, lifted the weighty successful beyond a very ordinary strike bag to the bench by the door and sat now and then which had produced just down to stare at it. It was heavy-very enough, as Dan said, "to keep 'em rootheavy. He hadn't supposed Jim had so ing after more.” And there had been no much dust as that meant. But Jim was opportunity for Jim to store away a hidalways such a close-mouthed, saving fel- den hoard, even with his partner's knowllow, you couldn't tell what he might edge. Dan had seen the little satchel, as have.
part of Jim's kit, scores of times, but