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Abstract: A standard distance target disc (diameter: 38.2 cm.) was fixed 50 metres from the observer, on a ground strip of 230 metres, and S was asked to divide the strip into equal sections using the 50 metre target as the standard. Carrying a set of discs, E displayed them one by one along the strip in ascending, and descending order, in accordance with directions given by S, thus arranging them in a line with the standard, with perceived "equi-distant-intervals" marked off. Ss were divided into 3 groups. In each group, the experiments were made with a different set of discs. Thus in group A, the discs increased in size, proportionally to the standard disc, by degrees set out in Emmert's Law, in group B, the discs decreased in size consecutively by 20%, and in group C, the size of the discs was equal to the standard.Results: 1) In all the groups the perceived distances deviated from the physical distances, and the degree of error increased with every distance interval farther away from S. 2) In each group judgments showed some consistency; group A produced overestimation of distances, i.e. the perceived distances were greater than the physical distances; groups B and C produced underestimation of distances, but the former showed greater underestimation.From the relationship between disc sizes and values of distance judgments, a formula was derived for computing disc sizes for best distance judgments. To verify this formula, another set of discs whose sizes were computed from the formula were tested on another group of Ss, and this yielded quite accurate judgments, of equi-distant-intervals. This study revealed that in a particular distance range there is a functional relationship between target size and accuracy of distance judgment, and that the latter, therefore, can be quantitatively predicted.

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