LECTURE XVIII

§ I. Temporal Course of Ideas. § II. The Personal Difference
OF Astronomers ; Eye and Ear Method. § III. Method of
Registration. § IV. Reaction-time. § V. Temporal Determina¬
tion OF Mental Processes.

§  I

WE have solved the problem of determining the ideational
content of consciousness at any given moment. The
next question that arises is that of ideational succession.
This falls into two parts : we must investigate, first, the time-
relations of ideational change, and, secondly, the qualitative
relations obtaining between the changing ideas. The actual
train of ideas must always be regarded under both its temporal
and qualitative aspects. A quantitative consideration of its
time-relations cannot, therefore, neglect the qualitative relations
of the single ideas, just because mental time-relations in general
must be essentially dependent upon the quality of conscious
content. At the same time, we shall find it,best to separate the
two sides of the problem so far, at least, as to deal predomi¬
nantly with temporal properties, and to attend only to those
more general and fundamental qualitative relations which
exercise a decisive influence upon them.

The coming and going, the rise and fall, of ideas have been
often enough described, though a guarantee for the absolute
correctness of the description cannot always be found. The
alleged facts rest partly upon all manner of speculative assump¬
tions, partly on the uncertain ground of introspection. Intro¬
spection unsupported by experiment can just as little lead to
any certain result here as it could in the inquiry regarding the
range of consciousness. And, unfortunately, the phenomena of
ideational succession with which introspection was specially
concerned happened to be just those which are least  of all