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‘thinking’ was not lost on Babbage or his contemporaries. Harry Wilmot Buxton, a junior col-
league of Babbage wrote:^7
the marvellous pulp and fibre of a brain had been substituted by brass and iron, he [Babbage]
had taught wheelwork to think, or at least to do the office of thought.
In 1833 Lady Annabella Byron, wife of the poet Byron and mother of Ada Lovelace wrote:^8
We both went to see the thinking machine (for so it seems).
The transference from mind to machine is clear in these descriptions.
The ‘mechanical notation’
Babbage quickly found that the intricate mechanisms and long trains of action in the Difference
Engine were impossible to hold in his mind at once. To alleviate the difficulty he developed
his ‘mechanical notation’, a language of signs and symbols of his own devising that he used to
formalize the description of his machines and their mechanisms (Fig. 24.2).
The notation is not a calculus. It is more in the nature of a symbolic description that specifies
the intended motion of each part and its relation to all other parts: whether a part is fixed (a
framing piece, for example) or free to move, whether motion is circular or linear, continuous or
intermittent, driver or driven, and to which other parts it is connected. Each part was assigned a
letter of our familiar Latin alphabet and various typefaces were used (italicized for moving parts
and upright for fixed framing pieces, for example). The physical form of parts and their motion
were indicated by up to six superscripts and subscripts appended to each identifying letter.
One of the superscripts (the ‘sign of form’) indicated the kind of part—gear wheel, arm lever,
spring, pinion, etc. Another index (the ‘sign of motion’) indicated the nature of movement—
reciprocating, linear or circular, or combinations of these. Annotations of this kind are liberally
distributed throughout the technical drawings.
The notation has three main forms:^9
1 a tabular form usually included on the drawing of the mechanisms (the drawings were
called ‘forms’)—the table is a compilation or index of the individual notations that
appear on the drawing and was used as an easy way to locate particular parts;
2 timing diagrams (called ‘cycles’) that describe the phasing of motions in relation to
each other—that is, the orchestration of motion;
3 a flow diagram form (called ‘trains’) that depicts the chain of influence of parts on one
another.
Babbage was inordinately proud of the Mechanical notation, which he regarded as amongst
his finest inventions. He saw it as a universal language with application beyond science and
engineering. Two examples he gave of its extended use were the circulation of blood in birds
and the deployment of armies in battle. It represents a first level of abstraction and he used it
extensively as a design aid to describe the function of the mechanisms.
The fate of the notation, baroque in its intricacy and idiosyncratically novel, has been largely
one of obscurity. The notation pre-echoes what we would now call a ‘hardware description
language’ (HDL). Such languages rose to prominence again in the early 1970s to manage com-
plexity in computer circuit and system design, particularly in solid-state chip design where