FIG. 13.
The observer looking from A, with his eye midway between the bottom of the carriage and the rail, will see the diameter of the wheels gradually diminish as they recede. The lines 1.2 and 1.4 will appear to approach each other until at the point B they will come together, and the space, including the wheels, between the bottom of the carriage and the rail will there disappear. The floor of the carriage will seem to be sliding without wheels upon the rail 1.2; but the lines 5.6 and 7.8 will yet have converged only to C and D.
The same phenomenon may be observed with a long row of lamps, where the ground is a straight line throughout its entire length as represented in [Figure 14].
FIG. 14.
The lines 1.2 and A D will converge at the point D and the pedestal of the lamp at D will seem to have disappeared, but the line 3.4, which represents the true altitude of the lamps, will only have converged to the point C.
A narrow bank running along the side of a straight portion of railway, upon which poles are placed for supporting the wires of the electric telegraph will produce the same appearance, as shown in [Figure 15].
FIG. 15.