both intervals, and which we must suppose to be present in all other
cases; and second, the particular lengthening effect which a change in
locality produces upon the interval in which it occurs. These two
factors may work in conjunction or in opposition, according to
conditions. The bare constant error does not remain exactly the same
at all times for any individual and is probably less regular in
tactual time than in auditory or in optical time, according to the
irregularity actually found and for reasons which will be assigned
later.


3. The third group of experiments introduced the factor of variation
in intensity of stimulation. By the introduction of a loop in the
circuit, containing a rheostat, two strengths of current and
consequently of stimulus intensity were obtained, either of which
could be employed as desired. One intensity, designated as _W_, was
just strong enough to be perceived distinctly. The other intensity,
designated as _S_, was somewhat stronger than the intensity used in
the preceding work.

In the first instance, sixty series were taken from Subject _B_, with
the conditions the same as in the experiments of Group 1, except that
two types of series were taken; the first two stimulations being
strong and the third one weak in the first type (_SSW_), and the order
being reversed in the second type (_WSS_). The results gave values of
_ET_ of 5.27 secs. for _SSW_ and 5.9 secs. for _WSS_.

In order to get comprehensive qualitative results as rapidly as
possible, a three-second standard was adopted in the succeeding work
and only one compared interval, also three seconds, was given,