the curve. Most of the construction was of wood, but the final section of 227 feet (69 metres) over the street was in iron as proposed for future rapid transit construction. Photos exist of the train posed on this section. The line had differing construction techniques: Wooden construction of the cheapest possible kind, suitable "for yard use, not for traffic" -from the beginning of the line to the shed's west door. Wooden construction, with low track following the contour of the ground -through the shed to the start of the main curve. Wooden construction, with continuous grade secured by increasing the heights of the wooden support posts -around the main curve. Wooden construction beginning level but with variable grades thereafter created by varying pole heights -end of main curve to end of second curve. The latter had the steepest grade, at 6.5%. Iron construction, increasing in height until the street crossing was reached at a heigh of 14 feet (4.25 metres) above the ground was reached. Then came a level stretch across the street to the end buffers. This was deliberately built with a slight curve but out of straight track girders to show that the system did not need to have specially curved girders to negotiate shallower curves. A photo exists of the deliberately kinked track. Macke's Three-Rail System The Meigs system had a three-rail competitor proposed for Boston between 1888 and 1891, and discussed by the Massachusetts state legislature. Unlike with the Meigs system, no demonstration line was built. It featured two load-bearing rails and a third traction rail in a gully between the two, with vertical driving wheels attached to the rail by wrap-round flanges. Description of Meigs system Overview Block quotations in the following description are from the 1886 Scientific American article, and the description is based on this. The basic premise for the design of the system was to make the street-level footprint of the line as narrow as possible, to ameliorate the problem of shadowing created by conventional urban elevated railroads. This entailed a single row of iron pillars of variable height, connected by single horizontal girders. On top of these girders was a pair of load-bearing rails, close together. In between the rails was a row of short posts, bearing a thick third rail. Each item of rolling stock (locomotive, tender or passenger car) had two trucks or bogies, each with four wheels.