ographers, but wrote in long-hand, so that he could speak
much faster than they could write. What he did, accordingly, was
undoubtedly to give the first copyist a start on the first letter he
wished to send, then turn to the second and give him a start on the
second letter, and so on, getting back to the first in time to keep
him busy. Quite an intellectual feat, certainly! But not a feat
requiring absolutely simultaneous attention to several different
matters. In a small way, any one can do something of the same kind. It
is not impossible to add columns of numbers while reciting a familiar
poem; you get the poem started and then let it run on automatically
for a few words while you add a few numbers, switch back to the poem
and then back to the adding, and so on. But in all this there is no
doing of two things, attentively, at the same instant of time.

You may be able, however, to combine two acts into a single
cooerdinated act, in the way just described under the head of
distraction, and give undivided attention to this compound act.

The Span of Attention

Similar to the question whether we can attentively perform more than a
single act at a time is the question of {262} how many different
objects we can attend to at once. The "span of attention" for objects
of any given kind is measured by discovering how many such objects can
be clearly seen, or heard, or felt, in a single instant of time.
Measurement of this "span" is one of the oldest experiments in
psychology. Place a number of marbles in a little box, take a single
peek into the box and see if you know how many marbles are there. Four
or five you can get in a single glance, but with more there you become
uncertain.

In the laboratory we have "exposure apparatus" for displaying a card
for a fifth of a second or less, just enough time for a single glance.
Make a number of dots or strokes on the card and see whether the
subject knows the number on sight. He can tell four or five, and
beyond that makes many mistakes.

Expose letters not making any word and he can read about four at a
glance. But if the letters make familiar words, he can read three or
four words at a glance. If the words make a familiar phrase, he gets a
phrase of several words, containing as many as twenty letters, at a
single glance.

Expose a number of little squares of different colors, and a
well-trained subject will report correctly as many as five colors,
though he cannot reach th