Les regrets de Babbage

Quand Charles Babbage (1791-1871), publie «Passages from the Life of a Philosopher» au soir de sa vie, il avertit le lecteur qu'il ne s'agit pas d'une autobiographie, car la vie d'un savant importe moins que ses travaux. Des travaux, il en a produit beaucoup sur des sujets les plus divers. Pourtant il est amer : son \oeuvre majeure n'a pas été reconnue à sa juste valeur dans son pays. Pire : elle n'a jamais vraiment vu le jour. Le ton est donné dès la dédicace à Victor Emmanuel II, roi d'Italie.
In 1840 the King Charles Albert, invited the learned of Italy to assemble in his capital. At the request of her most gifted Analyst, I brought with me the drawings an explanations of the Analytical Engine. These were thoroughly examined, and their truth acknowledged by Italy's choicest sons.

To the King, your father, I am indebted for the first public and official acknowledgement of this invention.
Sous une autosatisfaction et un détachement affectés, la suite est tout aussi amère : depuis les longues pages consacrées à ses démarches pour obtenir des financements, à ses difficultés à être exposé ou publié en Angleterre, jusqu'aux tout aussi longues pages sur ses amis savants italiens, allemands, suédois ou français qui (eux) ont reconnu sa valeur.

Le chapitre XXVI «Street nuisances» éclaire quelque peu les interactions de Babbage avec ses contemporains.

During the last ten years, the amount of street music has so greatly increased that it has now become a positive nuisance to a very considerable portion of the inhabitants of London. It robs the industrious man of his time ; it annoys the musical man by its intolerable badness ; it irritates the invalid ; deprives the patient who at great inconvenience has visited London for the best medical advice, of that repose which, under such circumstances, is essential for his recovery ; and it destroys the time and the energies of all the intellectual classes of society by its continual interruptions of their pursuits.
...et de lister tous les «intruments de torture» ainsi que les différentes nationalités et classes sociales coupables de les utiliser dans les rues à toute heure du jour et de la nuit. Incluant parmi les «nuisances de rues» l'usage immodéré et éminemment périlleux des cerceaux par les enfants, Babbage énumère toutes ses tentatives pour faire cesser ces scandales, et en appelle aux forces de l'ordre, à la promulgation d'une loi et à la création d'associations anti-nuisances...  non sans reconnaître implicitement que la vigueur de son combat n'était peut-être pas étrangère au fait que certaines de ces nuisances aient pu lui être explicitement destinées (vous l'auriez parié ?). Et pourtant... ! Quand il explique le principe de son Analytical Engine dans le chapitre VIII, quelle clarté, quelle puissance visionnaire !
It is known as a fact that the Jacquard loom is capable of weaving any design which the imagination of man may conceive. It is also the constant practice for skilled artists to be employed by manufacturers in designing patterns. These patterns are then sent to a peculiar artist, who, by means of a certain machine, punches holes in a set of pasteboard cards in such a manner that when those cards are placed in a Jacquard loom, it will then weave upon its produce the exact pattern designed by the artist.

Now the manufacturer may use, for the warp and weft of his work, threads which are all of the same colour; let us suppose them to be unbleached or white threads. In this case the cloth will be woven all of one colour; but there will be a damask pattern upon it such as the artist designed.

But the manufacturer might use the same cards, and put into the warp threads of any other colour. Every thread might even be of a different colour, or of a different shade of colour; but in all these cases the form of the pattern will be precisely the same- the colours only will differ.

The analogy of the Analytical Engine with this well-known process is nearly perfect.

The Analytical Engine consists of two parts:-

1st. The store in which all the variables to be operated upon, as well as all those quantities which have arisen from the result of other operations, are placed.

2nd. The mill into which the quantities about to be operated upon are always brought.

Every formula which the Analytical Engine can be required to compute consists of certain algebraical operations to be performed upon given letters, and of certain other modifications depending on the numerical value assigned to those letters.

There are therefore two sets of cards, the first to direct the nature of the operations to be performed - these are called operation cards: the other to direct the particular variables on which those cards are required to operate - these latter are called variable cards.


The Analytical Engine is therefore a machine of the most general nature. Whatever formula it is required to develop, the law of its development must be communicated to it by two sets of cards. When these have been placed, the engine is special for that particular formula. The numerical value of its constants must then be put on the columns of wheels below them, and on setting the Engine in motion it will calculate and print the numerical results of that formula.

Every set of cards made for any formula will at any future time recalculate that formula with whatever constants may be required.
Pensez qu'il y a encore 30 ans, les programmes étaient effectivement transmis aux ordinateurs par un paquet de cartes perforées. Comme le dit la citation de Byron que Babbage a placé en exergue du chapitre : «Man wrongs and Time avenges». Comme il le rappelle dans sa dédicace, Babbage est invité à Turin en 1840, et peut exposer ses idées à des auditeurs attentifs. L'un d'eux Louis-Frédéric Ménabréa (1809-1896), natif de Chambéry, deviendra une des figures de la vie politique italienne après l'indépendance. En attendant, ce n'est qu'un jeune ingénieur, à qui l'on confie la tâche de résumer les exposés de Babbage, et de les publier1.
Some time after the appearance of his memoir on the subject in the ``Bibliothèque Universelle de Genève,'' the late Countess of Lovelace informed me that she had translated the memoir of Menabrea. I asked why she had not herself written an original paper on a subject with which she was so intimately acquainted? To this Lady Lovelace replied that the thought had not occurred to her. I then suggested that she should add some notes to Menabrea's memoir; an idea which was immediately adopted.

We discussed together the various illustrations that might be introduced: I suggested several, but the selection was entirely her own. So also was the algebraic working out of the different problems, except, indeed, that relating to the numbers of Bernoulli, which I had offered to do to save Lady Lovelace the trouble. This she sent back to me for an amendment, having detected a grave mistake which I had made in the process.

The notes of the Countess of Lovelace extend to about three times the length of the original memoir. Their author has entered fully into almost all the very difficult and abstract questions connected with the subject.

These two memoirs taken together furnish, to those who are capable of understanding the reasoning, a complete demonstration- That the whole of the developments and operations of analysis are now capable of being executed by machinery.
De nombreux travaux ont été consacrés à la figure attachante d'Ada Lovelace (1815-1852), et à son influence sur Babbage ; mais il est impossible de savoir quelle part elle a vraiment prise dans la conception de la Machine Analytique. Elle est parfois considérée comme l'auteur du premier algorithme de l'histoire, celui qu'elle décrit pour les nombres de Bernoulli. Mais nous avons vu que Babbage affirme s'en être chargé «to save Lady Lovelace the trouble». Ce qui est évident à la lire, c'est qu'elle avait parfaitement compris le fonctionnement de la machine, et surtout qu'elle en avait imaginé le potentiel, avec un bon siècle d'avance. Voici ce qu'elle écrit.
The operating mechanism can even be thrown into action independently of any object to operate upon (although of course no result could then be developed). Again, it might act upon other things besides number, were objects found whose mutual fundamental relations could be expressed by those of the abstract science of operations, and which should be also susceptible of adaptations to the action of the operating notation and mechanism of the engine. Supposing, for instance, that the fundamental relations of pitched sounds in the science of harmony and of musical composition were susceptible of such expression and adaptations, the engine might compose elaborate and scientific pieces of music of any degree of complexity or extent.


It seems to us obvious, however, that where operations are so independent in their mode of acting, it must be easy, by means of a few simple provisions, and additions in arranging the mechanism, to bring out a double set of results: firstly, the numerical magnitudes which are the results of operations performed on numerical data. (These results are the primary object of the engine.) Secondly, the symbolical results to be attached to those numerical results, which symbolical results are not less the necessary and logical consequences of operations performed upon symbolical data, than are numerical results when the data are numerical.


The distinctive characteristic of the Analytical Engine, and that which has rendered it possible to endow mechanism with such extensive faculties as bid fair to make this engine the executive right-hand of abstract algebra, is the introduction into it of the principle which Jacquard devised for regulating, by means of punched cards, the most complicated patterns in the fabrication of brocaded stuffs. It is in this that the distinction between the two engines lies. Nothing of the sort exists in the Difference Engine. We may say most aptly, that the Analytical Engine weaves algebraical patterns just as the Jacquard-loom weaves flowers and leaves.


The bounds of arithmetic were however outstepped the moment the idea of applying the cards had occurred; and the Analytical Engine does not occupy common ground with mere ``calculating machines.'' It holds a position wholly its own; and the considerations it suggests are most interesting in their nature. In enabling mechanism to combine together general symbols in successions of unlimited variety and extent, a uniting link is established between the operations of matter and the abstract mental processes of the most abstract branch of mathematical science. A new, a vast, and a powerful language is developed for the future use of analysis, in which to wield its truths so that these may become of more speedy and accurate practical application for the purposes of mankind than the means hitherto in our possession have rendered possible. Thus not only the mental and the material, but the theoretical and the practical in the mathematical world, are brought into more intimate and effective connexion with each other. We are not aware of its being on record that anything partaking in the nature of what is so well designated the Analytical Engine has been hitherto proposed, or even thought of, as a practical possibility, any more than the idea of a thinking or of a reasoning machine.
«The executive right-hand of abstract algebra» : une belle définition pour Xcas n'est-ce pas ?

         © UJF Grenoble, 2011                              Mentions légales