20 TECHNOLOGY. 
the rail is generally a uniform layer of broken stone, into which the sleepers 
are imbedded and firmly settled with beetles until no sensible sinking takes 
place. The cross-sills are rough hewn in order to remove the sap-wood, and 
their ends generally project 12-18 inches beyond the sleepers. The longi- 
tudinal sills are let into the cross-sills, and are either wedged or fastened by 
means of chairs. In the South it is best to use yellow pine for these, as 
that wood warps and cracks less from the effects of the heat than oak. 
The arrangement of the timber is shown in pl. 2, jigs. 25 and 26, with a 
rail as in jig. 39. The longitudinal sills or stringers will have a depth of 
from six to ten inches, according to the strength of the rail and the proposed 
burdens ; the supports may be four feet apart, and the length of each 
stringer should not be less than twenty feet in order to avoid too frequent 
breaks, which in one track should always be opposite the middle of a 
stringer on the opposite track. In the same way the joints of the rails 
should never correspond with those of the stringers. 
Superstructures of this kind being very expensive in countries where 
timber is scarce, they have not been introduced to a great extent in Europe; 
even in the United States the lower sleepers have frequently been dispensed 
with on that account, the cross-sills resting in beds of broken stone. In the 
place of wooden supports a stone superstructure has also been employed, 
consisting of two continuous parallel walls of stone, connected by cross-ties 
of stone, which may be replaced by wooden sills of one foot square, or else 
by iron rods and binders, where stones of sufficient length cannot be 
obtained. The direct attachment of the rails to stone being very injurious, 
as stated above, wood must be interposed between the rail and the support. 
Plank of two inches in thickness will suffice for rails of two inches depth, 
but heavier string-pieces will be required for rails of less size. Grooves of 
the width of the wooden stringers are cut into the stone of such a depth 
that the top of the rail is at least two inches above the rough-dressed stone 
surface, in order to allow room for the flanges of the wheels. The fastening 
of the rail may be done as in pl. 2, jig. 83; jigs. 27 and 28 show a super- 
structure of this kind. 
The rails used with continuous supports are of very different forms and 
sizes, varying from three pounds to eight and even thirteen pounds per 
linear foot. The ends are generally cut off at an angle of 45°, sometimes 
also in the form of a metre joint (fig. 40), which is preferable. The rails 
are fastened to the supports by spikes or screws, the holes for which are 
one eighth of an inch longer than required, in order to allow for the effect 
of temperature upon the iron. Under the joints are placed plates of zine 
or iron, to prevent the ends of the rails from being pressed into the wood. 
An excellent form for the flat rail is that shown in jig. 39, weighing nine 
pounds per linear foot, which was devised for the New Orleans and Nash- 
ville railroad. /%g. 41 shows the ordinary flat rail. Of many other different 
forms we only instance that proposed by Strickland, the bredge or U-raal 
(fig. 88), weighing 133 pounds per linear foot, and a similar one by J. K. 
Brune (jigs. 48 and 44), which has a more convex bearing surface than the 
preceding. 
600 
