Applying this model of visualisation to historic time, a number of issues emerge. The objectives O and the idea I can be thought of as expressing the ontology of whatever will be depicted. They comprise a set of beliefs and assumptions about ‘reality’. They seem to those who hold them to be just ‘how things are’. The model M, view V and picture P comprise the corresponding epistemology — the means by which that ontology can be represented (fig. 5). Of course in the case of time, the reality in question is intangible and invisible, making it even more susceptible to differences in conceptualisation than if we were dealing with a graspable referent such as a tree or a chair. Time has been variously conceived as static and as moving, as irregular and as uniform, as linear and as cyclic. A given culture may hold two or more models of time together, using them for different purposes, such as a linear model to identify reigns, typically using a sense of before and after, or a cyclic model to plan agriculture, using seasonal landmarks. Time’s very existence is debated, not just in metaphysics but in physics [27]. Both Bergson [28] and Benjamin [29] object to the image of time as a uniform, quasi-spatial container in which events are situated the way buildings are placed along a highway. They see this as the dominant ontology of time, and one that they wish to challenge. More recently, work in the digital humanities has also questioned the ‘scientific’ ontology of time as too ruler-like, certain and linear to house the uncertainties and subjectivities of humanities scholarship [30]. The question of time’s very existence is raised in a different way by Gell [31] when he asks whether all cultures do in fact have a model of time: he suggests that while a society may have a model of the relationship between events, between now and the past, between the past and the future, etc., it may not necessarily have a model of time per se at all. In summary, time, even historical time, is not ‘out there’ in some universally agreed form, waiting to be depicted. It will be conceptualised in particular ways, which will tend to lead to particular representations. In a given culture, a particular ontology will dominate, to the extent that it is largely taken for granted as simply ‘how time is.’
      It has been suggested by various authors [32] that the eighteenth century is the period when our modern conception of time, as a continuous, uniform space in which events are situated, emerges in mainstream European culture. This is the very spatialisation of time that later offends Bergson and Benjamin. Parallel arguments have been made about the earlier emergence of clock time. In the medieval period, the notion of what constitutes an hour shifts from adjusted portions of an unequal day and night to the uniform one-twenty-fourths of a day measurable by clocks [33]. The effects of clockwork on thought have been traced in relation to the emergence of capitalism by Mumford [34], in metaphors of regulation in medieval writing by Mason Bradbury and Collette [35], in narrative and the emerging novel of the seventeenth century by Sherman [36], in the emergence of nationality by Anderson [37], and in eighteenth century cosmology by Bolter [38], to cite only a few examples. This widely remarked influence of clock mechanism on concepts of passing time offers an immediate warning of the extent to which forms of representation alter the thing they claim to represent. The epistemological tools available have an influence on the ontology (fig. 6). How reality simply seems to be, is altered by the means for representing it.
      Sometimes attempts may be made to force a new ontology by redesigning the representation. The rotation of the shadow on a sundial gave the later mechanical clock its rule for being correctly ‘clockwise’, a sense of correctness which was then exported to the southern hemisphere, even though there the shadow on a sundial turns the opposite way. Such cultural forcing was resisted in 2014 by the regime of Morales in Bolivia, which shifted to ‘anticlockwise’ clocks to promote non-imposed values [39], an attempt to re-construe the epistemology to recover a marginalised ontology.

 

O → I → M → V → P
O ← I ← M ← V ← P

Fig. 6. The technologies and traditions bound up in the epistemology of a domain in turn affect its ontology. The understanding of how ‘things really are’ is altered by the means of representation.

 

      One aspect of the ontology of ‘all’ time that remained more or less constant throughout the period under discussion was its estimated overall duration of 6,000 years, despite the many controversies over the details — ‘that learned Noise and Dust of the Chronologist’ as Locke termed it [40]. The order of magnitude was hardly ever in doubt. Soon however a number of disturbances would occur. Growing awareness of the antiquity of continuous Chinese civilisation would undermine confidence in the West’s claims over the totality of history. The theories of Hutton and others would push the origins of the Earth back by thousands, and later millions, of years. The new model of ‘all time’ would force changes to the representation of universal histories: at the most basic level, it simply became impossible to map time linearly to a reasonable number of engraved sheets. Fortunately for Barbeau and his contemporaries, all of time was still of a just-manageable scope, best illustrated by the Chronographie ou Description des Tems of Barbeu-Dubourg [41] which mapped on a linear scale all time from the Creation using 16.5 metres of paper. Finally, a further disturbance, of particular significance to French chronographers, would be the resetting of the origin of the calendar to a new Year 1 during the Revolution [42]. In this connection, McCallam [43] points out the political weight attached to new forms of measurement at this period, including the conscious modernism of the shift to new forms of mensuration in the eighteenth century, set against the inherited arbitrariness of seigneurial measures. This increased emphasis on uniform measurement is at one with the increased admiration, generally in radical circles, for mechanism and mechanical metaphors [44].

 

Homogeneous, empty time

 

      The conceptualisation of Time as uniform and dimensioned in ways that are analogous to Space can be traced to the Cartesian conception of number as mappable to a line — a number-line — and to space when extended over two or more dimensions. The writings of Descartes, particularly the Compendium Musicae of 1619, are suffused with the ideas of clear representation, of grasping magnitudes at a glance, and specifically of line-lengths which correspond to number [45]. In the posthumous Regulae of 1684 we find Descartes claiming that there is a graphical equivalent to any variable quantity: ‘the infinite multiplicity of figures is sufficient for the expression of all the differences in perceptible things [46]’. Once number takes the form of a dimensioned line in the seventeenth century, time follows. Eighteenth-century writers wrote enthusiastically of the novel Newtonian shift to seeing time as a dimension: ‘absolute, true, and mathematical [47]’. D’Alembert’s article on chronology for the Encyclopedie opens with the quotation: In tempore, dit Newton, quoad ordinem successionis, in spatio quoad ordinem situs locantur universa (‘All things, said Newton, are placed in time as to order of succession; and in space as to order of situation [48]’) which could be a model for Barbeau’s mappemonde.