those of more primitive life. Such attention
without effort is known as _*secondary passive
attention_. Examples are furnished by the
geologist's attention to the strata of the
earth, the historian's to original manuscripts,
the manufacturer's to by-products, the merchant's
to distant customers, and the attention
which we all give to printed symbols and scores
of other things unnoticed by our distant ancestors.
Here our attention is similar to passive
attention, though the latter was the result
of inheritance, while our secondary passive
attention results from our individual efforts
and is the product of our training.

Through passive attention my concentration
upon a ``castle in Spain'' may be perfect
until destroyed by a fly on my nose. Voluntary
attention may make my concentration
upon the duty at hand entirely satisfactory

till dissipated by some one entering my office.
Secondary passive attention fixes my mind
upon the adding of a column of figures, and it
may be distracted by a commotion in my vicinity.
Thus concentration produced by any
form of attention is easily destroyed by a
legion of possible disturbances. If I desire
to increase my concentration to the maximum,
I must remove every possible cause of