Tuesday, 1 September 2009

Arithmetic scale for time

Making a list of historic events tends to produce a dense block of information with no wasted space between items. The focus is on the events, rather than on the time that they occupy. Periods with a lot of events take a lot of space, while those with few take less. This clearly has benefits in terms of economy of materials, and means that the user need not, for instance, turn a dozen almost empty pages in order to find an isolated incident. However this ‘packed array’ approach makes it difficult to see temporal patterns in the data, such as interesting alignments, gaps and clusters.

Here is a simple example of a time list which makes no use of empty space and simply puts one event after another: BBC timeline of Nepal

A slightly more sophisticated use of time-space is to have empty rows or columns for years (or other units of time) when nothing happened. This tends to also produce the result that each page or section represents the same amount of time. This approach goes back quite a long way.
Title page of Helwig [Helvicus], Christopher. 1687. The Historical and Chronological Theatre.
From the collection of Prof Michael Twyman. Photo: Stephen Boyd Davis.

In Helvicus’ Historical and Chronological Theatre, the case is made for spacing chronology in equal intervals. But Helvicus credits his predecessor, Scaliger, one of the most famous chronologers (about whom more another time) with introducing the practice. In the introductory note Of the equal Intervals of Centenaries and Denaries, i.e. Hundreds and Tens of Years he says:
What our Author (Scaliger) chiefly aim’d at, in his first contrivance of this Systeme, was a distribution of Years, from the beginning of the World down to our own times, into equal spaces or distances of Centenaries of Decads (viz. Hundreds and Tens of years) by reason of the singular use or advantage which therefrom result. For thus, the Reader cannot chuse but remember and declare, by the year of the World, or of Christ, wherein every Exploit or History happen’d, how many years the one was from the other; provided he make himself well acquainted with the Order and Continuation of the principal Governments of each Monarchy, by which guidance the Series of History will easily be retain’d in Memory. For every Page of his did contain one Hundred entire years; so it must on necessity fall out, that the correspondent Number of the next Page over against it should differ therefrom a Centenary of years. As for Example: the Peloponnesian War (which happened in the year of the World 3519) was placed in the end of the second Cell, (Area) or Denary: Opposite thereto, in the same part of the  following Page, was set down the Battel at Arbela, wherein Darius was subdued, and the Power was invested in Alexander; whence it appear’d, that there was the space of One Hundred years between the beginning of the Peloponnesian War, and the time wherein the Grecian Monarchy began.
So he is arguing that this design produces benefits in terms of:
  1. remembering sequences, including how long events lasted (the Order and Continuation of the principal Gorvernments); 
  2. the estimation of intervals between events.

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