Picking up the eraser, Dick carefully erased the last two lines
that he had set down.

Then, as though working under a new inspiration, he went ahead
setting down line after line of the demonstration of this difficult
problem. Only once did he halt, and then for not more than thirty
seconds.

Dunstan went through a halting explanation of his problem. Then
Captain Abbott called:

"Mr. Prescott!"

Taking up the short pointer, Dick rattled off the statement of
the problem. Then he plunged into his demonstration, becoming
more and more confident as he progressed.

When he had finished Captain Abbott asked three or four questions.
Dick answered these without hesitation.

"Excellent," nodded the gratified instructor. "That is all, Mr.
Prescott."

As Dick turned to step to his seat he pulled his handkerchief
from the breast of his blouse and wiped the chalk from his hands.
All unseen by himself a narrow slip of white paper fluttered
from underneath his handkerchief to the floor.

"Mr. Prescott," called Captain Abbott, "will you bring me that
piece of paper from the floor?"