used.
This is a form of short-exposure apparatus. The essential idea is to
furnish a field upon which the subject may for a moment fasten his
attention, and then to substitute for this field another containing
certain prepared test-material. This last field is exposed for but a
brief instant and removed, and the subject is then called upon to report
all that he has seen during the last exposure. Tests of this kind have
demonstrated that the range of visual attention is a comparatively
constant quantity with each individual, having but little relation to
general ability or intelligence and being but little affected by practice.

It matters not how painstaking the individual may be, he will fail in
a test of this kind and at work of this kind if the type of attention
that Nature gave him is unfitted for such an "expanded" watchfulness.
Yet in any type of work requiring a focusing of the attention upon a
minute operation so as to note nice discriminations and detect subtle
differences, he might prove a most excellent worker.

[Sidenote: _Kinds of Testing Apparatus_]

The kind of apparatus, the method to be employed and the place for
the experiment are all matters that vary with the conditions of the
special problem. The apparatus may be simple and easily devised, or it
may be intricate and the result of years of investigation and a large
expenditure of money.

If there seems to you to be anything impracticable in the employment
of tests in the manner we have indicated, please remember that for
many years those seeking employment as railroad engineers have been
required to pass tests for color-blindness, tests just as truly
psychological as any that we have here referred to and differing from
them only in respect to the character and complexity of the qualities
tested.

[Sidenote: _Analysis of Different Callings_]

Every calling can be analyzed and the mental elements requisite for
success in that particular line can be scientifically disentangled.
Methods for testing the individual as to his possession of any one
or all of the mental elements required in any given vocation may
then be devised in the psychological laboratory.

Furthermore, definite and scientific exercises can be formulated
whereby the individual may train and develop special senses, faculties
and powers so as the better to fit himself for his chosen field of
work.

[Sidenote: _Exercises for Developing Special Faculties_]

The use of the experi