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 package of them all! Take an instance. Let a leadsman cry,
'Half twain! half twain! half twain! half twain! half twain!' until it
become as monotonous as the ticking of a clock; let conversation be
going on all the time, and the pilot be doing his share of the talking,
and no longer consciously listening to the leadsman; and in the midst of
this endless string of half twains let a single 'quarter twain!' be
interjected, without emphasis, and then the half twain cry go on again,
just as before: two or three weeks later that pilot can describe with
precision the boat's position in the river when that quarter twain was
uttered, and give you such a lot of head-marks, stern-marks, and side-
marks to guide you, that you ought to be able to take the boat there and
put her in that same spot again yourself! The cry of 'quarter twain' did
not really take his mind from his talk, but his trained faculties
instantly photographed the bearings, noted the change of depth, and laid
up the important details for future reference without requiring any
assistance from him in the matter. If you were walking and talking with
a friend, and another friend at your side kept up a monotonous
repetition of the vowel sound A, for a couple of blocks, and then in the
midst interjected an R, thus, A, A, A, A, A, R, A, A, A, etc., and gave
the R no emphasis, you would not be able to state, two or three weeks
afterward, that the R had been p