constructing the viaduct is so combined as to be capable of giving passage upon the road to the rolling stock of the large lines during the stoppage of the daily passenger trains.

(3.) The tracks are connected at the extremities by a curve that has the proper incline to compensate for the difference in level between the two, and which has a sufficiently large radius to allow the slope of the track to be kept within the limits admitted. The running of the trains is thus uninterrupted.

(4.) When two lines of different directions bisect one another, a special arrangement permits the passengers from one line to pass to the other by means of what is called a "tangent" station, without the trains of one line crossing the tracks of another, the purpose of which arrangement is to avoid those accidents that would inevitably occur through the crossing of a track by the trains of a transverse line.

(5.) The rolling stock is arranged in a manner that allows the entrance and exit of the passengers to be effected with great promptness.

In ordinary avenues, comprising a roadway and two sidewalks, the elevated railway is placed in the axis of the roadway at a sufficient height to prevent it interfering with the passage of carriages, say 14¾ feet above the surface, while in boulevards or avenues of great width, having contre-allees¹ bordered by a double row of trees, it is installed in one of the contre-allees.

In the first case (Fig. 1), the viaduct is wholly metallic, while in the second it comprises masonry arches surmounted by a metallic superstructure. The viaduct is formed of independent spans supported by metallic piers that rest upon masonry foundations (Fig. 2).

Fig. 1.—PROJECT FOR A PARISIAN ELEVATED RAILWAY.