e hand that
held the gun. This case, sir, will make a noise."

"Well," said the priest patiently, "and what did you do next?"

"I reckon you'll be shocked," replied Greywood Usher, "as I know you
don't cotton to the march of science in these matters. I am given a good
deal of discretion here, and perhaps take a little more than I'm given;
and I thought it was an excellent opportunity to test that Psychometric
Machine I told you about. Now, in my opinion, that machine can't lie."

"No machine can lie," said Father Brown; "nor can it tell the truth."

"It did in this case, as I'll show you," went on Usher positively.
"I sat the man in the ill-fitting clothes in a comfortable chair, and
simply wrote words on a blackboard; and the machine simply recorded the
variations of his pulse; and I simply observed his manner. The trick is
to introduce some word connected with the supposed crime in a list of
words connected with something quite different, yet a list in which it
occurs quite naturally. Thus I wrote 'heron' and 'eagle' and 'owl', and
when I wrote 'falcon' he was tremendously agitated; and when I began to
make an 'r' at the end of the word, that machine just bounded. Who else
in this republic has any reason to jump at the name of a newly-arrived
Englishman like Falconroy except the man who's shot him? Isn't that
better evidence than a lot of gabble from witnesses--if the evidence of
a reliable machine?"

"You always forget," observed his companion, "that the reliable machine
always has to be worked by an unreliable machine."

"Why, what do you mean?" asked the detective.

"I mean Man," said Father Brown, "the most unreliable machine I know of.
I don't want to be rude; and I don't think you will consider Man to be
an offensive or inaccurate description of yourself. You say you observed
his manner; but how do you know you observed it right? You say the
words have to come in a natural way; but how do you know that you did it
naturally? How do you know, if you come to that, that he did not observe
your manner? Who is to prove that you were not tremendously agitated?
There was no machine tied on to your pulse."

"I tell you," cried the American in the utmost excitement, "I was as
cool as a cucumber."

"Criminals also can be as cool as cucumbers," said Brown with a smile.
"And almost as cool as you."

"Well, this one wasn't," said Usher, throwing the papers about. "Oh, you
make me tired!"

"I'm sorry," said the ot