Bauhaus-Universität Weimar

Experimental Psychology: A Manual of Laboratory Practice, Vol. II: Quantitative Experiments, part 2: Instructor's Manual
Titchener, Edward B.
The Metric Methods 
(3) We found by our first procedure (p. 96 of the text) that 
the curve of distribution of the RL is not symmetrical. In that 
case, however, we took the median value of the RL to be 1.7 
Paris lines. The derivation in terms of Gauss’ Law gave 1.88. 
We have now to examine the course of the curve in the light of 
this value, 1.88, and of its measure of precision, h = 0.49. 
The method is simple. We replace the value RL and h by the 
numbers 1.88 and 0.49 in all the seven expressions (D — RL) h, 
and then look up in Fechner’s Fundamental Table—paying re¬ 
gard to sign !—the seven «-values that correspond to the result- 
ing Lvalues. 
We thus obtain : 
0.5 1.0 1.5 
Observed n 
0.14 0.40 
Calculated n 
0.27 0.40 
Our previous inference is confirmed : within the limits taken, the 
curve of distribution of the RL drops towards the axis of abscis¬ 
sas in the region of the higher D’s more quickly than it rises from 
that axis in the region of the lower. Nevertheless, there is noth¬ 
ing to suggest that our assumption of the validity of Gauss’ Law 
was wrong,—that some other law of distribution holds in its 
place. The results show a distinct tendency to approximate to¬ 
wards the values required by Gauss’ Law ; and those that diverge 
from it diverge sporadically, and thus bear upon their face the 
marks of experimental inaccuracy. 
(4) It is better to make RL the variable magnitude, for the 
following reasons, (a) The source of the accidental errors may 
be physical, physiological or psychological. In so far as it is psy¬ 
chological, we may more naturally refer the variation to the limen 
than to the objective D. (b) The limen does, as a matter of ob¬ 
served fact, vary from experiment to experiment, whereas it is of 
the essence of good experimental work that D remain constant 
throughout the series in which it is employed. When, therefore, 
we say that the limen = RL ± 8, we are stating a fact ; when we 
say that the compass distance = D ± 8 we are introducing a 
mathematical fiction, (c) In most experiments, we seek to de¬ 
termine more than one type of limen. Thus, in the present in¬ 
stance we may determine both the RL and the UL: in work by 
the method of constant stimulus differences we may determine,.


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