it clearer. Most people, if you describe a train of events
to them, will tell you what the result would be. They can
put those events together in their minds, and argue from them
that something will come to pass. There are few people,
however, who, if you told them a result, would be able to
evolve from their own inner consciousness what the steps were
which led up to that result. This power is what I mean when
I talk of reasoning backwards, or analytically."

"I understand," said I.

"Now this was a case in which you were given the result and
had to find everything else for yourself. Now let me
endeavour to show you the different steps in my reasoning.
To begin at the beginning. I approached the house, as you
know, on foot, and with my mind entirely free from all
impressions. I naturally began by examining the roadway, and
there, as I have already explained to you, I saw clearly the
marks of a cab, which, I ascertained by inquiry, must have
been there during the night. I satisfied myself that it was
a cab and not a private carriage by the narrow gauge of the
wheels. The ordinary London growler is considerably less
wide than a gentleman's brougham.

"This was the first point gained. I then walked slowly down
the garden path, which happened to be composed of a clay
soil, peculiarly suitable for taking impressions. No doubt
it appeared to you to be a mere trampled line of slush, but
to my trained eyes every mark upon its surface had a meaning.
There is no branch of detective science which is so important