Sketch of the Analytical Engine invented by Charles Babbage, Esq.Menabrea, Luigi Federico
Science
Sketch of the Analytical Engine invented by Charles Babbage, Esq.
Menabrea, Luigi Federico
Babbage, Charles, 1791-1871; Numerical analysis
Let us consider a term of the form ; since the cards are
but a translation of the analytical formula, their number in this
particular case must be the same, whatever be the value of ; that
is to say, whatever be the number of multiplications required for
elevating to the th power (we are supposing for the moment
that is a whole number). Now, since the exponent indicates
that is to be multiplied times by itself, and all these
operations are of the same nature, it will be sufficient to employ one
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single operation-card, viz. that which orders the multiplication.
But when is given for the particular case to be calculated,
it will be further requisite that the machine limit the number of
its multiplications according to the given values. The process may
be thus arranged. The three numbers , and will be
written on as many distinct columns of the store; we shall designate
them , , ; the result
will place itself on the column . When the
number has been introduced into the machine, a card will order
a certain registering-apparatus to mark (), and will at the
same time execute the multiplication of by . When this is
completed, it will be found that the registering-apparatus has effaced
a unit, and that it only marks (); while the machine will now
again order the number written on the column
to multiply itself with the product written on the column
, which will give . Another unit is then effaced
from the registering-apparatus, and the same processes are continually
repeated until it only marks zero. Thus the number will be
found inscribed on , when the machine, pursuing its
course of operations, will order the product of by ; and
the required calculation will have been completed without there being
any necessity that the number of operation-cards used should vary
with the value of . If were negative, the cards, instead
of ordering the multiplication of by , would order its
division; this we can easily conceive, since every number, being
inscribed with its respective sign, is consequently capable of reacting
on the nature of the operations to be executed. Finally, if were
fractional, of the form , an additional column would
be used for the inscription of , and the machine would bring into
action two sets of processes, one for raising to the power ,
the other for extracting the th root of the number so obtained.
Public-domain text, read in full here on John Shaqi.
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