d upon, to assist justice
with information that his special knowledge and opportunities have
rendered accessible to him. You see the bearing of this?"

"You mean that I should note down what I have seen and heard and say
nothing about it until I am asked."

"Yes; if nothing further happens. But if you should be sent for again, I
think it is your duty to make further observations with a view, if
necessary, to informing the police. It may be, for instance, of vital
importance to identify the house, and it is your duty to secure the
means of doing so."

"But, my dear Thorndyke," I expostulated, "I have told you how I was
conveyed to the house. Now, will you kindly explain to me how a man,
boxed up in a pitch-dark carriage, is going to identify any place to
which he may be carried?"

"The problem doesn't appear to me to present any serious difficulties,"
he replied.

"Doesn't it?" said I. "To me it looks like a pretty solid impossibility.
But what do you suggest? Should I break out of the house and run away up
the street? Or should I bore a hole through the shutter of the carriage
and peep out?"

Thorndyke smiled indulgently. "The methods proposed by my learned friend
display a certain crudity inappropriate to the character of a man of
science; to say nothing of the disadvantage of letting the enemy into
our counsels. No, no, Jervis; we can do something better than that.
Just excuse me for a minute while I run up to the laboratory."

He hurried away to Polton's sanctum on the upper floor, leaving me to
speculate on the method by which he proposed that a man should be
enabled, as Sam Weller would express it, "to see through a flight of
stairs and a deal door"; or, what was equally opaque, the wooden
shutters of a closed carriage.

"Now," he said, when he returned a couple of minutes later with a small,
paper-covered notebook in his hand, "I have set Polton to work on a
little appliance that will, I think, solve our difficulty, and I will
show you how I propose that you should make your observations. First of
all, we have to rule the pages of this book into columns."

He sat down at the table and began methodically to rule the pages each
into three columns, two quite narrow and one broad. The process occupied
some time, during which I sat and watched with impatient curiosity the
unhurried, precise movements of Thorndyke's pencil, all agog to hear the
promised explanation. He was just finishing the last page when th