every book, but we turned over every leaf in each volume, not
contenting ourselves with a mere shake, according to the fashion of
some of our police officers. We also measured the thickness of every
book-cover, with the most accurate admeasurement, and applied to each
the most jealous scrutiny of the microscope. Had any of the bindings
been recently meddled with, it would have been utterly impossible
that the fact should have escaped observation. Some five or six
volumes, just from the hands of the binder, we carefully probed,
longitudinally, with the needles."

"You explored the floors beneath the carpets?"

"Beyond doubt. We removed every carpet, and examined the boards with
the microscope."

"And the paper on the walls?"

"Yes."

"You looked into the cellars?"

"We did."

"Then," I said, "you have been making a miscalculation, and the
letter is not upon the premises, as you suppose."

"I fear you are right there," said the Prefect. "And now, Dupin, what
would you advise me to do?"

"To make a thorough re-search of the premises."