ntity are concerned. In the case
of musical notes, however, the very greatest difference is found in the
ability of different individuals to distinguish pitch. So also the
distinguishing of distance and direction in relation to sound is an
acquired ability, in which different people will greatly differ.
Finally, to interpret the external relations involved in the sound, that
is, whether the cry is that of an insect or a bird, or, if it is the
former, from what kind of bird the sound is proceeding, this evidently
is a phase of sense interpretation in which individuals differ very
greatly. Yet an adequate development of the sense of hearing might be
supposed to give the individual an ability to interpret his surroundings
in all these ways.

=Power of Sense Perception Limited: A. By Interest.=--It should be
noted, however, that so far as our actual life needs are concerned,
there is no large demand for an all-round ability to interpret sensuous
impressions. For practical purposes, men are interested in different
objects in quite different ways. One is interested in the colour of a
certain wood, another in its smoothness, a third in its ability to
withstand strain, while a fourth may even be interested in more hidden
relations, not visible to the ordinary sense. This will justify one in
ignoring entirely qualities in the object which are of the utmost
importance to others. From such a practical standpoint, it is evidently
a decided gain that a person is not compelled to see everything in an
object which its sensuous attributes might permit one to discover in it.
In the case of the man with the so-called untrained sense, therefore, it
is questionable whether the failure to see, hear, etc., is in many cases
so much a lack of ability to use the particular sense, as it is a lack
of practical interest in this phase of the objective world. In such
processes as induction and deduction, also, it is often the external
relations of objects rather than their sensory qualities that chiefly
interest us. Indeed, it is sometimes claimed that an excessive amount of
mere training in sense discrimination might interfere with a proper
development of the higher mental processes.

=B. By Knowledge.=--From what has been discovered regarding the learning
process, it is evident that the development of any sense, as sight,
sound, touch, etc., is not brought about merely by exercising the
particular organ. It has been learned, for instance, that th