Mathematical philosophy, a study of fate and freedom; lectures for educated laymen, by Cassius J. Keyser.

THE MATHEMATICS OF PSYCHOLOGY 375
an upper limit-an end as well as a beginning. Observe
that
stimulus
n=log1,r
stimulus
=loge A. log+, e.
Let us now write S=n, R =stimulus -A and C=logx+, e.
Then we have
S =C log R
Such, then, is Fechner's formulation of what he called
the Psychophysical Law. We must not fail, if we are to
understand it, to note very carefully, the meaning of the
symbols. Observe that S, the initial letter of the word
sensation, denotes nothing but a cardinal number. Note
that the constant C depends on r and that r, which is
the same for the sensations of a given sense department,
differs for different departments. Note also that R is
not the stimulus that produces S, as it is commonly said
to be (by Professor James, for example), but that it is
the quotient of that stimulus divided by A, and that A
depends upon the sense department under investigation.
The sense departments that have been most investigated are those of light, muscular sensation, pressure,
warmth and sound. For these the values of r, as reported
by Professor Wundt, are as follows:
For light, r = about f
For muscular sense, r = about
For pressure, r = about 3
For warmth, r = about 1
For sound, r = about ~