Notions sur la machine analytique de M. Charles Babbage

The First Computer Programs Ever Published. First edition, the journal issue, of the first published account of Charles Babbage's Analytical Engine - and, printed a full year before Ada Lovelace's celebrated English translation of it, the first appearance in print of computer programs: the operation-tables setting out, step by step, how Babbage's projected machine would be driven through a calculation. The paper appeared only in this Swiss journal, which survives chiefly in institutionally-stamped subscription copies; the present example is uncommon in carrying no library stamp at all. Babbage had conceived the Analytical Engine in 1834, in the aftermath of his uncompleted, government-funded Difference Engine. It was to be a general-purpose programmable calculating machine - never built in his lifetime, yet embodying in its design most of the essential features of the modern digital computer. From the Jacquard loom Babbage took control by punched cards; from the vocabulary of the textile trade he took the names of its parts, calling the processing unit the 'mill' and the memory the 'store'. Its signal feature, and the hardest for his contemporaries to grasp, was its capacity to govern its own course: to advance or back its cards according to the results of its own previous calculations - what is now called conditional branching. Babbage's countrymen showed little curiosity about the machine, and he never presented it publicly in England. The one occasion on which he set out its principles before a company of competent scientists came abroad. In 1840, pressed by the Turin astronomer Giovanni Plana (1781-1864), he travelled to the congress of Italian scientists at Turin, carrying drawings, models and sheets of his mechanical notation, and over several mornings in his apartments expounded the Engine to Plana, Menabrea, Mossotti, MacCullagh, Plantamour and others. The difficulty, as Anthony Hyman records, lay less in the mechanism than in the concept: Mossotti could accept that the machine handled arithmetic and even algebra, but balked at how it might take a course of action determined by its own results - until Babbage, by a series of examples, brought his listeners to see how the Engine could advance or back its operation cards by any number of steps. The Turin discussions, Hyman writes, were 'the only public presentation before a group of competent scientists during Babbage's lifetime' of the ideas behind the modern digital computer. Plana had meant to write up the lectures himself, but he was old and ill, and the task fell to the youngest of the group - Luigi Federico Menabrea (1809-1896), a captain of military engineers ('capitaine du génie militaire', as the paper styles him) who taught mechanics at the Turin military academy and would rise to become Prime Minister of the newly united Kingdom of Italy. Babbage sent him further explanations to supplement the notes taken at Turin; Menabrea rewrote the article entirely, and on 27 January 1842 wrote that he would give it its last touches and send it to Geneva. It appeared that October, as number 82 of the Bibliothèque Universelle de Genève. Babbage had chosen the venue deliberately, wanting the machine's existence not to rest, as he put it, upon his 'unsupported testimony': the discovery, he wrote, was 'so much in advance of my own country, and I fear even of the age' that he had selected the celebrated Turin academy as the place of its first announcement. Menabrea's account said little of mechanical detail. What it did instead was decisive: to show what the machine could do, he printed several tables - 'cartons des opérations', 'cartons des variables' - setting out the ordered sequence of operations through which the Engine would be directed to solve a given problem, from a difference-table for the series of squares to the working of a pair of simultaneous equations. These tables, reproduced from those Babbage had brought to Turin, are what Hook and Norman call 'the first exam.…