28 ANNUAL OF SCIENTIFIC DISCOVERT. 



nbove the water line, but, -when filled, another five feet Avill bo 

 add I'll. 



The ano^les of the crib were armored with iron two and a half 

 inches tliiek. Tin' three distinet walls or shells, one wilhin an- 

 other, WL-re t'ach construeted of TJ-int-h S([uare timln'r, eaulkcd 

 watei'-ti;^ht like a ship, and all three braced and girded together 

 in every direction, with irons and timbers, to the utmost possible 

 pitch of nu'i'hanical strength. Within these sjjaces were con- 

 struct«'d fifteen caulked and water-tight coniparlmcnts, Avhich were 

 filled with clean rublde stone, alter the crib was placed in i)osi- 

 tion. By this means the crib was sunk to the bottom, where it 

 Mas finnly moor«d by cables reaching in every direction to Inige 

 screws forced ten feet into the bed t)f the lake. The water in 

 which it was sunk was thirty-five; feet deep, leaving five feet of the 

 structure altove the surface. This was in June, lUGo. The crib 

 had cost .'?inO,(Hi(). 



The crib stands 12 feet above the water line, giving a maximum 

 area of 1,"J00 feet whicli can be exposed at one sweep to the acti(jn 

 of the waves, reckoning the resistance as perpendicular. The 

 outside was thoroughly caulked, e(jual to a first-class vessel, with 

 three threads in each seam, the first and last iieing what is called 

 "horsed." Over all these there is a layer of lagging, which will 

 keep the caulking in jdace.and proti'ct the cril) proper from the 

 action of the waves. A covered i)latfonn or house was Ijuilt over 

 the crib, enabling the workmen to prosecute the work uninter- 

 rupted by rain or wind, and afi'ording a protection for the earth 

 brought up from the excavation, and permitting it to be carried 

 away by sctnvs, whose return carg()es ha\ e been l)ricks for the 

 lining of the tunnel. The top of the cylinder will be covered 

 with a grating to keep out floating logs, fish, &c. A sluice made 

 in the side of the crib will be opened to let in the water, and a 

 lighthouse will be built over all, serving the double purpose of 

 guarding the crib from injury by vessels,and of showing the way 

 to the harbor of Chicago. 



The next thing was to sink a water-tight shaft within the well 

 of the crib and into the bottom of the lake some 30 feet further, 

 making G6 feet in all below the surface of the water. Seven great 

 ii'on cylinders, each nine feet long, nine feet in diameter, two and 

 a half inches thick, and weighing 30,000 pounds, were cast for 

 this purpose. The seven iron cylinders, making the iron part of 

 the shaft, and 03 feet of it in height, Avere one by one connected 

 by bolts, and lowered to the bottom of the lake within the 30 feet 

 open space in the centre of the crib. In the next to the upjier of 

 these cylinders are the gates or A'alves b}^ which the water will 

 be let in to and shut out from the tunnel. The cylinders Avere 

 then, after having been brought to exactly the right position, 

 forced downward into the stiff, hard clay of the bottom some 25 

 feet, the Avater being Avholly excluded. 



The Avater was now pum])ed out, the tojj of the shaft Avas closed 

 as nearly as possible air-tight, and a powerful air-i:)ump, driven by 

 steam, commenced to exhaust the air also. As fast as a vacuum 

 could be created, the atmospheric pressure, added to its OAvn 



