The word 'timeline'

The Oxford English Dictionary defines time-line as:

• a certificate of apprenticeship 
• an undulating line indicating small fractions of a second, by which the time or rate of some process may be measured
• a schedule, a deadline

The Dictionary’s earliest citation of a usage where time is arithmetically mapped to a surface or space is William James’ Principles of Psychology (1890). In his case, only one graphical component of the diagram is the time-line, rather than the whole design. Nevertheless it shows the key concept of events marked against a regular ‘clock’ of time, an idea fundamental to most of the examples discussed in my blog posts.

An early use of the word time-line in something like its present sense. The waves of the time-line here represent regular time intervals, while the reaction-line above it shows a pair of events. From p.86 of William James’ Principles of Psychology, Volume 1, 1890. Wellcome Library, London (http://images.wellcome.ac.uk/). Used with permission. Photo: Stephen Boyd Davis.

References
James, W. (1890), The Principles of Psychology. (2vols.) New York: Henry Holt. The whole book is online here: http://ebooks.adelaide.edu.au/j/james/william/index.html. The diagram appears in Chapter 3: On Some General Conditions of Brain-Activity. 
Oxford English Dictionary. (2011), ‘Timeline’ Online version June 2011 (Accessed 24 July 2011.) http://www.oed.com/ (subscription required).