n. Nothing short of perfection will do.
That faculty is memory. He cannot stop with merely thinking a thing is
so and so; he must know it; for this is eminently one of the 'exact'
sciences. With what scorn a pilot was looked upon, in the old times, if
he ever ventured to deal in that feeble phrase 'I think,' instead of the
vigorous one 'I know!' One cannot easily realize what a tremendous
thing it is to know every trivial detail of twelve hundred miles of
river and know it with absolute exactness. If you will take the longest
street in New York, and travel up and down it, conning its features
patiently until you know every house and window and door and lamp-post
and big and little sign by heart, and know them so accurately that you
can instantly name the one you are abreast of when you are set down at
random in that street in the middle of an inky black night, you will
then have a tolerable notion of the amount and the exactness of a
pilot's knowledge who carries the Mississippi River in his head. And
then if you will go on until you know every street crossing, the
character, size, and position of the crossing-stones, and the varying
depth of mud in each of those numberless places, you will have some idea
of what the pilot must know in order to keep a Mississippi steamer out
of trouble. Next, if you will take half of the signs in that long
street, and CHANGE THEIR PLACES once a month, and still manage to know
their new positions accurately on dark nights, and keep up with these
repeated changes without making any mistakes, you will understand what
is required of a pilot's peerless memory by the fickle Mississippi.

I think a pilot's memory is about the most wonderful thing in the world.
To know the Old and New Testaments by heart, and be able to recite them
glibly, forward or backward, or begin at random anywhere in the book and
recite both ways and never trip or make a mistake, is no extravagant
mass of knowledge, and no marvelous facility, compared to a pilot's
massed knowledge of the Mississippi and his marvelous facility in the
handling of it. I make this comparison deliberately, and believe I am
not expanding the truth when I do it. Many will think my figure too
strong, but pilots will not.

And how easily and comfortably the pilot's memory does its work; how
placidly effortless is its way; how UNCONSCIOUSLY it lays up its vast
stores, hour by hour, day by day, and never loses or mislays a single
valuable packa