Barbeau is thus strongly connected to cartographic practice, and might well, on mapping historic time to the page, have adopted the pictorial approach from cartography favoured by Martignoni. However, he interpreted cartography in a very different way. His chart in fact connects the new cartographic fashion to the old typographic tradition, though he modifies both significantly. He assisted, after the death of the Abbé Lenglet du Fresnoy in 1755, in re-editing the latter’s Tablettes Chronologiques, traditional tabular books of historic chronology published in 1763 [69] and 1778 [70], and must have been familiar with two earlier publications by Lenglet, the 1729 Méthode pour étudier l’Histoire [71] and the accompanying Tables Chronologiques [72], which appeared when Barbeau was nineteen. The four folio sheets of Lenglet’s Tables together comprise a matrix of roughly synchronised columns of dates, two sheets for dates before the birth of Christ, and two for dates after. They distribute kingdoms by column, and dates by row, with the earliest dates at the top. Lenglet claims that his is une méthode que je présente autant aux yeux qu’à l’esprit (a method that I present as much to the eyes as to the intellect) [73], which suggests a striking visual design, though in fact the layout harks back to the many tabular, typographic productions of earlier years. In particular, the widths of the columns are more or less arbitrary, being dictated by the amount of information they need to contain, and the vertical intervals are not arithmetic, simply listing one event after another regardless of the time elapsing between. Barbeau would subtly but significantly rework this design on a more rigorous, a more arithmetic, basis, true to both aspects of his own description: ‘ordre & précision’ (order and precision) [74].
      In 1750 Barbeau produced his Mappemonde, described later as a carte ingénieuse & vraiment nouvelle, où il a su réunir en un seul systême la géographie, la chronologie & l’histoire (an ingenious and truly new chart in which he knew how to unite, within a single system, geography, chronology and history) [75]. Although Barbeau’s design is entitled Mappemonde, it is clearly not an ordinary map and indeed his Explication immediately asserts, as Lenglet also had done, that for a historian to be familiar with geography is a prerequisite. For that purpose he recommends maps by Delisle and Buache [76]. There was a long tradition, dating back at least to Chytraeus in 1563, of regarding chronology and geography as the two ‘eyes of history’ [77], a tradition explicitly referenced by Barbeau who erroneously attributes its origin to Cicero [78], After a court préliminaire (short preparation) in geography, one is ready to make use of the Mappe-monde. Barbeau immediately establishes the principle on which the chart is constructed:

 

1º. Les Divisions Géographiques, marquées au haut de la Carte avec les noms des Pays, & continuées jusqu’au bas par des Lignes perpendiculaires. Ces Divisions forment ainsi pour chaque Pays une Colomne, où se voient indiqués les Evenemens principaux, & les Révolutions, depuis les premières Peuplades faites après le Déluge jusqu’à présent.
2º. Les Divisions Chronologiques (qui ont rapport aux Temps ou aux Années) tracées par des Lignes horizontales, qui partent des chiffres marqués aux deux côtés de la Carte; laquelle est divisée de cette seconde manière par longues Bandes, selon les espaces de Temps ou de Siécles.

1st. The Geographic Divisions, indicated at the top of the Chart by the names of Countries, and continued down to the bottom of the Chart by perpendicular Lines. These divisions form thus for each Country a Column in which can be seen marked the principal Events and Revolutions, from the first Tribes created after the Flood down to the present time.
2nd. The Chronological Divisions (which relate to Ages or to Years) marked by horizontal Lines springing from the numbers shown on two sides of the Chart; which is thus divided a second time by long Bands, corresponding to the spaces of Time or of Centuries [79].

 

The phrase espaces de Temps is noteworthy. Time is now space, and the whole chart captures in two dimensions la Géographie & la Chronologie, c’est-â-dire, la Science des Lieux & la Science des Temps (Geography and Chronology; which is to say, the Knowledge of Places and the Knowledge of Dates) [80]. On reading Barbeu’s Explication an important difference from Lenglet’s Tables stands out: the emphasis on measurement. Though Barbeau does not say so explicitly, we are essentially dealing with a coordinate space. When describing the representation of each regime, he makes clear that the width shows the region’s extent, and the height the duration (La largeur marque son étendue, & la hauteur sa durée) [81]. He emphasises the underlying geographic basis: la Géographie de tous les Ages en étant comme la bas & en déterminant toutes les Colomnes, il ne peut y avoir d’interruption. Comme chaque Pays a été habité depuis les premières Peuplades faites après le Déluge, les Dominateurs n’ont point manqué: ils ont seulement changé (since the Geography of all Ages serves as foundation and determines every Column, there can be no interruption. As each Country has been inhabited since the first Peoples created after the Flood, Rulers have never been wanting: they have simply changed) [82]. The result is that every point on the surface has a meaning, indicating in context both geographic and temporal extents, which are treated as essentially similar phenomena.
      Like the earlier Martignoni, Barbeau suggests that — his design being visual rather than textual — it supports more than one form of interrogation. He cites Biblical authority (Acts 17:26) for his combining genealogy (which in fact appears hardly at all), time and geography [83]. He rather undermines his claim for the primacy of the visual by providing long narrative explanations of various histories traceable in the Explication. Some of this narrative is genuinely explicatory, enabling best use of the chart by a detailed walk-through of two columns, those for France and Spain. Downwards investigation of the changes in each of those two kingdoms over time is described in detail, and then Les autres peuvent se suivre de même, pour remarquer les Révolutions de chaque Pays, depuis les plus anciens Temps, jusqu’â présent. (The others can be followed in the same fashion, to discover the Revolutions in each Land, from the most ancient Times to the present.) [84]. As expected, the chart may also be explored horizontally: En suivant une des Lignes horizontales d’un bout à l’autre, on voit l’état de tous les Pays du Monde dans chaque Siécle, ou dans une certain Période de Temps; par exemple à la Naissance de J.C. (Following one of the horizontal lines from one end to the other, we see the condition of every Country in the World in each Century, or at a particular Period in time; for example, at the Birth of Christ) [85].