But this devil of a man held his banknote before me whichever way I looked, and I had only two pounds left in the world! "Are you going to fight a duel ?'' I asked.
"I have already told you what I am going to do," he answered.
I waited a little.

The infernal bank-note still tempted me.

In spite of myself, I tried him again.
"If I teach you the trick," I persisted, "will you undertake to make no bad use of your lesson ?" "Yes," he said, impatiently enough.
I was not quite satisfied yet.
"Will you promise it, on your word of honor ?" I asked.
"Of course I will," he answered.

"Take the money, and don't keep me waiting any longer." I took the money, and I taught him the trick--and I regretted it almost as soon as it was done.

Not that I knew, mind, of any serious consequences that followed; for I returned to London the next morning.
My sentiments were those of a man of honor, who felt that he had degraded his art, and who could not be quite sure that he might not have armed the hand of an assassin as well.