Chap. VII.
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rails are let in about } of an inch throughout, except at the joinings of the rails, where thechairs occur. The chairs are 6 inches square at the base, and | of an inch in thickness,and the rails are bolted down to them securely, the hole in the rail being made a littlelarger than the bolt, to allow for expansion. The bolt and nut weigh 7 ounces, and thechair 10£ pounds ; the latter is held by four spikes, 6 inches in length, the heads of whichpassed over the edge of the chair.
In a mile of road there were 71 tons of rail, 5910 pounds of chairs, 4524 pounds ofspikes, and 481 pounds of bolts and nuts.
About 30 miles from Philadelphia is a tunnel, the length of which is 1932 feet, the width19 feet, and the internal height 17 feet. The sides are cut quite perpendicular, as high as10 feet 9 inches, and above this the section is a half oval, rising 6 feet 8 inches; there is nolining of masonry except at the ends, the rock it passes through being the Grauwacke slate,and sufficiently strong without it.
Beyond the northern end of the tunnel, the Schuylkill is crossed by a stone bridge,18 feet 4 inches wide; there are four spans, each 72 feet, and 3 piers of 8 feet; the roadwayis 24 feet above the level of the river. The versed sine of the arches is 16 feet 6 inches ; thearch is the segment of a circle whose radius is 47 feet 6 inches. Below the water thefoundations are carried down to 10 or 12 feet in depth ; lloman cement was used instead ofmortar, and the whole of the superstructure is executed with cut stone.
Baltimore and Ohio Jiailroad extends 80£ miles, the road bed is in width 26 feet;41 miles from Baltimore there is an inclined plane, in length 2150 feet, rising 80 ; this isfollowed by another, 3000 feet in length, and 100 feet rise ; the summit is 813 feet abovemid tide, and is called Parr’s Spring Ridge. From thence the line descends by an inclinedplane, 3200 feet in length, and 160 feet in height, and by another 1900 feet in length, and81 feet in height, after which the gradients vary from 37 to 52 feet per mile.
The viaducts are all of stone excepting two; between Baltimore and the Potomac thereare thirty-three.
The rails are sometimes laid on granite sills, and at others on timber sleepers ; the ironrails are in 15 feet lengths, each pierced with eleven oblong holes, to receive iron pins.
Baltimore and Port Deposite Road is 95 miles in length, its maximum inclination is 20feet per mile, and its minimum radius of curvature 2000 feet.
Under each line of rails is a sill sawed out of white pine, 8 inches by 6 inches, in lengthsof from 12 to 40 feet. These are laid flat in longitudinal trenches ; on these, at distancesof 3 feet from centre to centre are cross timbers of white oak and chestnut, 8 feet in lengthand about 8 inches by 6 ; each has four notches, two on the lower side, 8 inches wide, and twoon the upper, 7^ inches, in which is a wedge for the purpose of making fast the longitudinalpiece; the thickness left between the upper and lower notch is always 2£ inches. Thelower notches embrace the under sills, and are made to fit, so that no lateral movement cantake place.
The rails are nearly rectangular on their section, and weigh 40 pounds per yard; theyare 2£ inches wide at bottom, 2^ at top, and 1^ inch in height; their length varies from 17feet 9 inches to 18 feet 3 inches, and their ends are cut obliquely to an angle of about 60°.Each is vertically perforated by five holes, by means of which they are secured to thelongitudinal timbers ; the ends of the rails are lodged on plates of rolled iron, J inch inthickness, and about 5$ by 4j inches. On the upper side of these plates are two smallledges, extending their whole length parallel to each other, through which the rail passes,and is prevented from having any lateral movement. Two 9-inch bolts keep the platessecure.
Baltimore and Susquehanna railroad is in length 56 miles; its summit level is 1000 feetabove that of high water ; its steepest ascent is 84 feet per mile, and descent 59 feet. Theleast radius of curvature is 950 feet.
Lexington and Ohio railroad is 92^ miles in length, the minimum radius of curvature is1000 feet, and its maximum inclination 30 feet per mile. Where it descends the valleyof the Green River is an inclined plane 4000 feet in length, and 240 feet in height.
To these may be added the Portland, Saco and Portsmouth in the depaftment of Maine ,in length 50 miles; Concord, in the same department, 35 miles; in Massachussetts , theBoston and Maine , 17 miles; Berkshire, 21 miles; Felchburg, 50 miles ; Nascliua andLowell , 14 miles ; Northampton and Springfield ; Old Colony, and some others. In new York is the Attica and Buffalo , in length 31 miles; Auburn and Rochester , 78 miles;Auburn and Syracuse , 26 miles; Buffalo and Magara, 22 miles; Erie, 53 miles; Long Island , 96 miles; Utica and Schenectady 78 miles; Reading, 94 miles; South Carolina and Columbia, 202 miles, and a great many others in progress; those already completedamount to nearly 2700 miles in length.
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