Difference Engine
The real beginnings of computers as we
know them today lay with an English mathematics professor, Charles
Babbage. Frustrated at the many errors he found while examining calculations for
the Royal Astronomical Society, Babbage declared, "I wish to God these
calculations had been performed by steam!" With those words, the automation of
computers had begun.
A difference engine is a
special-purpose mechanical digital
calculator, designed to tabulate
polynomial functions. Since
logarithmic and
trigonometric functions can be
approximated by polynomials, such a machine is more general
than it appears at first.
The conversion of the original design
drawings into drawings suitable for engineering manufacturers' use
revealed some minor errors in Babbage's design, which had to be
corrected. Once completed, both the engine and its printer worked
flawlessly, and still do.
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A replica of the Difference Engine in the London Science Museum
This machine used the decimal number system and was powered by cranking
a handle. The
British government initially financed the project, but
withdrew funding when Babbage repeatedly asked for more money while
making no apparent progress on building the machine.
Babbage went on to
design his much more general
analytical engine but later produced an improved difference
engine design (his "Difference Engine No. 2") between 1847 and 1849.
Inspired by Babbage's difference engine plans,
Per Georg Scheutz built several difference engines from 1855
onwards; one was sold to the British government in 1859.
Martin Wiberg improved Scheutz's construction but used his
device only for producing and publishing printed
logarithmic tables.
The difference engine and printer were constructed to tolerances
achievable with
19th century technology, resolving a long-standing debate
whether Babbage's design would actually have worked. One of the reasons
formerly advanced for the non-completion of Babbage's engines had been
that engineering methods were insufficiently developed in the Victorian
era.
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