14 | TECHNOLOGY. 
impinge against the rails, and the outside wheels must pass over a longer 
space than the inside wheels, and therefore are dragged a certain distance 
over the rail, which causes great friction and torsion in the axles. It has 
been attempted to diminish the dragging of the exterior wheels and the 
friction of the flanges by giving a conical form to the tire of the wheels and 
elevating the exterior rail in curves by a certain amount, by means of 
which the force of gravity will counteract the tangential velocity to some 
extent. Nevertheless the resistance of friction remains very prejudicial in 
practice, and its amount depends on the length of the radius of curvature, 
on the width of the track, on the length and weight of the train and its - 
speed. It will become still more sensible if faults exist in the laying of the 
rails and in the construction of the cars. 
2. ConsTRUCTION OF A Ramroap. In proceeding to the actual work of 
construction after having perfected the plans, the attention of the engineer 
must be directed to a great variety of points, all of which are essential to 
the ultimate success of the road. We will now follow the several steps of 
the construction of a railroad. 
a. Grading. In railroads the principle that they should be dry and 
secure from inundation is of still greater importance than in common roads, 
as it is essential to the duration of the superstructure. 
In order to give solidity to embankments the newly filled earth must 
always be spread equally over the road. HEmbankments of no great depth 
may be made solid by ramming and rolling, but if they are considerable, 
the filling should be done in layers and the material so spread as to produce 
a firm combination of the masses of earth. Ifthe earth is to be moved but 
a short distance, wheelbarrows may be employed, but for distances of any 
considerable length two-wheeled carts are used, which are often made to 
run on temporary railroad tracks. Embankments should not be formed by 
filling from one side to the other, raising the whole at once (s¢de-forming), 
but rather by embanking out from one end in the whole width of the bank, 
by which some solidity is given to the lower portion by the pressure of the 
superincumbent earth as well as that of the carts and workmen. When 
side-forming is resorted to it should be done as indicated in pl. 2, jig. 1 
(that is to say, the filling should be commenced from the bottom for some 
distance along the embankment, by means of a guide-way, b, supported on 
trestles, cc, filling first the part ad of the slope, next de, and so on. The 
core of the profile is considerably solidified in this manner, but the method 
is expensive and slow). For very wide embankments (jig. 2), the two out- 
side portions dc and fg may be completed first with the aid of temporary 
tracks, and the interior part de filled afterwards. All embankments are at 
first to be made higher than the required grade of the road by the probable 
amount of settling of the earth. Very high banks should be allowed at 
least a winter season to settle before the superstructure is laid, a precaution 
to be recommended for all embankments. ‘The inclinations of the side 
slopes should always be less than that which the earth naturally assumes ; 
it will generally be from 1 upon 1 to 1 upon 1}, and according to cireum- 
stances even 1 upon 2 and less. 
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