# Bauhaus-Universität Weimar

### Volltext Experimental Psychology: A Manual of Laboratory Practice, Vol. II: Quantitative Experiments, part 2: Instructor's Manual (2 (2))

Titel:
Experimental Psychology: A Manual of Laboratory Practice, Vol. II: Quantitative Experiments, part 2: Instructor's Manual
Person:
Titchener, Edward B.
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit11940/431/
```254
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.
D
We thus obtain :
0.5 1.0 1.5
2
3
4
5
Observed n
O.IO
0.14 0.40
0.65
0.80
0.87
0.96
Calculated n
0.17
0.27 0.40
0-53
0.78
0.93
0.985.
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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