The 1910 partial build of the Analytical Engine

 

Doron Swade, who as Curator of Computing at the Science Museum led the team that built a working replica of Babbage's Difference Engine No 2 to celebrate the 200th anniversary of Babbage's birth, joined the Plan 28 project in 2010 and the next year the project was accepted by the Computer Conservation Society, which has been involved in many historical computer reconstructions in the UK, notably Colossus.

Also in 2011, work commenced on digitizing the Babbage archive as the initial step towards building a working prototype of the Analytical Engine. In his bi-annual report to the Computer Conservation Society in Spring 2015 Swade reported  progress with understanding Babbage's mechanical notation, Babbage’s language of signs and symbols that he used to describe and specify his engines.

However a year later he was less upbeat, reporting:

We have been pecking away at Babbage’s original design drawings for some while now and have found with regret that we are unable to reverse engineer a coherent and consistent understanding of the Analytical Engine from the mechanical drawings alone. There are some 300 drawings and some 2200 Notations – descriptions of the mechanisms using Babbage’s language of signs and symbols. There were three phases of design - early, middle, and late.There is overlap between these, there are ad hoc upgrades, and only fragmentary explanation, where there is explanation at all.

...

To achieve a more comprehensive understanding of the designs Tim Robinson in the US is going through the entire Babbage archive (over 7000 manuscript sheets) and producing a cross-referenced searchable data base. The purpose of this is to marshal all known sources so that we have a bounded idea of all relevant material. The intention is to reveal any explanations and/or drawings that Babbage might have left that have not yet come to light.

Over the next year Swade himself completed a review of the 26 volumes of Babbage’s Scribbling Books – Babbage’s scratchpad daybooks, comprising 8,100 folio sides - with the specific purpose of this review was to identify all material specifically relating to the Mechanical Notation. In the same time frame Robinson had produced a searchable database of all catalogued material with related content fully cross-referenced covering all technical drawings and related Notations.

The problem with going through Babbage's notebooks is revealed in the Autumn 2017 report:

As reported previously the volume of material is substantial and its organisation is not conducive to systematic study: it not indexed or themed by topic, nor is it rigorously chronological. Time and time again Babbage revisits the same or related topics over a period of decades, and these entries, many of which are cryptic, are dispersed through the twenty-five volumes comprising some 7-8,000 manuscript sheets.

Now in the latest, Winter 2017, report comes the hint that however much cross referencing is done there may be gaps that cannot be filled:

The question of the levels of completeness of the various designs is critical to a prospective build and new clues have emerged from the recent work. A manuscript in the Cambridge University Library contains a disconcerting observation by Babbage: that 'when some great improvement arose I only worked out enough to satisfy myself of its truth. I reserved the enquiry into many of its consequences as a treat when I otherwise felt indisposed to work' (1860). This has bleak implications for a definitive detailed design. 

Robinson has also found an entry in the Notbooks in which Babbage refers to Plan 13 as the 'most complete ever made' (1849). This Swade suggests can provide: 

datum set by Babbage himself by which to judge the best expectation of completeness and this promises to give us a first approximation of the size and nature of design gaps we might need to fill in the specification of a meaningfully buildable machine. 

The report concludes that continuing to mine the Notebooks for the searchable cross-referenced database remains the priority for the coming months, so the team is sticking with its daunting task.

So can the engine be built?

It depends on what you mean. If the aim is to build an engine that Babbage would have built then it might not be possible as perhaps Babbage never resolved all of the details - "I only worked out enough to satisfy myself of its truth".

The more subtle question is whether it is possible to build an engine that Babbage would have acknowledged as "Yes that's my analytical engine." This seems more possible, but it is going to be a matter of getting more into his head and seeing the same truth he saw, and this is possibly not as satisfying to a historian.

More Information

Plan 28 Winter 2017 Report

Plan 28

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