The essentials of mental measurement . on is now made that the relationship between the * 6. E. Miiller, Ueber die Maassbestimmungen des Ortssinnes der Haut mittels deiMethode der richtigen und falsohen Falle, Pflugers Archiv fur die ges. Physiologic, 1879,XIX. pp. 191—235, especially par. 5 et seg.: also Die Oesichtspunkte und die Tatsachender paychophysiachem Mefhodik, Wiesbaden, 1904, par. 11, where the classical descriptionof this method will be found. B. & T. 5 66 PSYCHOPHYSICS [ft. i stimulus s, and the frequency p with which the answer heavier is returned,is given by the equation ^_r *_
The essentials of mental measurement . on is now made that the relationship between the * 6. E. Miiller, Ueber die Maassbestimmungen des Ortssinnes der Haut mittels deiMethode der richtigen und falsohen Falle, Pflugers Archiv fur die ges. Physiologic, 1879,XIX. pp. 191—235, especially par. 5 et seg.: also Die Oesichtspunkte und die Tatsachender paychophysiachem Mefhodik, Wiesbaden, 1904, par. 11, where the classical descriptionof this method will be found. B. & T. 5 66 PSYCHOPHYSICS [ft. i stimulus s, and the frequency p with which the answer heavier is returned,is given by the equation ^_r *_e->-3)cfe = 0 (1). J -00 V (?) That is to say, it is assumed that the successively increasing percentagesof answers heavier correspond to the increasing area of the portion ofa Normal Curve which is shaded in Fig. 9, as the point s moves tothe right in that figure. To obtain this equation in a more convenient form for our purpose, ^^* h{s-T) = t - V (2). This corresponds to measuring the stimuh in a special unit, and is the. T Fig. 9. To illustrate Mullers proceBS same device as that used in another connection later by Galton. The equation then becomes 1 rh(s-T) ^-VR)L ^-- (^)- By inserting in this equation the corresponding values of p and sfrom the table of data on p. 59, we obtain seven equations for twounknowns h and T, and as these equations are shghtly inconsistent withone another we have to decide how to calculate the most probablevalues of h and T. No pair of values will exactly satisfy all sevenequations. Instead of coming to zero they leave small residuals adopted the Method of Least Squares, an account of which willbe found on p. 44 in Chapter II. In passing a note must be made of the fact that Miiller assumedtacitly that these observation equations, being each based on the samenumber of experiments, are of equal importance or weight*. We shallallow this assumption to pass for the present but shall return to it later. Unfortunately, the equations are v
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