"Yes, gray hair."
"The color of his eyes was black."
"No, sir."
"Oh, yes."
"No, sir, they were clear blue eyes; I remember that well. Why did you say they were black?"
Jack laughed and answered:
"I was only aiding you to remember—working on the plan of a detective I've read about, who always worked on the negative track, when trying to develop positive facts from witnesses."
"By ginger! I never should have recalled the color of his eyes if you had not positively stated that they were black."
"Then we have verified the theory?"
"Yes, indeed."