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CHAPTER, XIIL
a pilot's needs.
but I bxo. wandering from what I was intending to do, that is, make
plainer than perhaps appears in the previous chapters, some of the
peculiar requirements of the science of piloting. First of all, there is
one faculty which a pilot must incessantly cultivate until he has
"brought it to absolute perfection. 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 j for this is eminently one of
the * exact^J 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 1' One cannot easily
realise what a tremendous thing it is to know every trivial detail of
twelve hundred Tnil.es 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 Biver in his head. And then if you will go
on until you know every street crossing, the character, size, and posi-
tion 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 posi-