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A device
which has fascinated me is the difference engine designed,
partially built and demonstrated by Charles Babbage. I had heard of
various attempts at modelling one of these machines, generally
unsuccessful. The original was built by a team of skilled artisans
under the guidance of Charles Babbage and cost in real terms about the
same as constructing a town.
It is believed that the original was never actually finished despite
years of effort.
I was amazed to see a working model at the annual Melbourne Society of
Model and Expermental Engineers (MSMEE) exhibition in 2004 held within
the Monash University Civil Engineering buildings. The model is
absolutely mesmerizing while it is performing is miracle of mechanical
mathematics. My two boys and I watched the machine working through
several calculations as its constructor and owner Graham Jost gave an
interesting and knowledgeable talk about how the machine works, even
taking suggestions from viewers for equations to be evaluated. The
remainder of this article is a reproduction of Grahams information card
he has on the display - I felt it best to use Grahams own words to
describe the model. Well done mate, a fantastic job at any time - but
to have built it in Meccano is outstanding!
-- START Graham's article the following text is reproduced with
permission and is © Copyright Graham Yost. --
Babbage Difference Engine No. 1 by Graham Jost
This Meccano model has been more of a constructional challenge to me
than any other to date! Strictly speaking, it is not a model at all,
but a fully working mechanism, realised using Meccano parts, of part of
a 'Difference Engine', similar to that first designed and demonstrated
by Charles Babbage , the 'father of computers', in 1832. The machine
calculates, automatically, successive values of polynomial expressions
using the 'Method of Differences' - hence Babbage's naming the
calculator a 'Difference Engine'.
By the early 19th century, the lack of accurate mathematical tables used
by scientists, actuaries, navigators and others had become a matter of
serious concern - comparisons of tables from different sources
frequently showed iconsistencies. These tables are based on
mathematical functions which can be approximated to any desired degree
of accuracy, over given ranges, by appropriate polynomial expressions.
The Difference Engine was seen by Babbage as a suitable device for
evaluating such polynomials, and hence the tables, utterly free from
error.
Difference
Engine No. 1 was the first of two designed by Babbage - a small portion
of No. 1 was the only working fragment of either of Babbage's
difference engines that was ever actually built.
I can take little credit for this model, other than to rightly claim to
have built it! Its extraordinary able and clever designer is Timothy
Robinson, an Englishman working in California, who has had a lifetime
interested in mechanical calculating machines. On discovering the
existence of his machine, I first communicated with him in July 2003
about it, and he has been unstintingly helpful and encouraging to me
ever since. I eventually succeeded in eliciting occasional correct
evaluations from my machine one year later (!) but have since managed
to improve its reliability considerably.
Meccano parts are not really of the required precision for such
mechanisms, and this model will sometimes produce an incorrect answer.
Nonetheless, it is an extraordinary achievment in Meccano, and its
designer deserves every credit.
First, second and third-order polynomials can be evaluated up to the
value 9999. I have tabulated the values of several of these, and invite
your suggestions as to which one(s) you would like the machine to
evaluate for you, against which you can then check for accuracy - or
otherwise.
Graham
Jost
-- END Graham's article --
The reader should note that Graham is very modest about his
achievement, the design you see in the photos is not the original
design. It has been improved by adding a two digit sequence counter so
you can see where the machine is up to in the calculation sequence and
has been motorised. I understand from Graham that this machine took
around a year to build. An amazing achievement, especially when you
consider that Babbage and his team of engineers, fitters & turners,
and other artisans seemingly never actually finished the real one.
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