Abstract
Parallel alleys are perceived to converge to one point. According to Allee Versuch it is verified that forward slightly outstretched alleys are perceived to be parallel. Two walls faced each other with forward out-stretched angle, such as Piazza Campidoglio, have been said to appear to be parallel. This view shoud be investigated by this study. The method is as follows; there are two wall modells (each 2.5m×5.0m), one is fixed on the ground, the other is horizontally rotated around the central axis, subjects stand on several observation points, experimenter rotate the rotative wall with slow velosity and record the angles through the sign which are given by subjects when the two are estimated to be parallel. The conclusion has come to; two walls shoud be faced each other with forward outstretched angle amount of 5°〜6°, wherever observation points are, to the end of appeared parallel.
