My original sources of enlightenment regarding Charles Hutton’s invention of contour lines were firstly Countryfile on TV (watched with my mum), second Wikipedia, third Edwin Danson’s book ‘Weighing the World’. Hutton was a computing wizard (long a verb before a noun): “These calculations were naturally and unavoidably long and tedious; and the more so as the business was in a manner quite new”.
The phrase that stuck: “Thus were ‘the great lines’ born” and that gave rise to the project title I had assumed came from Hutton – or Danson – but in one epic re-read I realised was in fact me!Hutton does not describe contours as ‘the great lines’, he only uses the phrase for triangulation lines (or ‘skeleton lines’ as they were also known): “to compute… such of the great lines in the survey whose extremities are visible … and from the various sets of triangles which can be formed”.As a visual artist (no historian, mathematician nor scientist) I am happy for the title to remain; there were so many ‘great’ lines invented for the purpose of mapping. And we all make mistakes, Hutton again: “I had frequently the mortification to find that the several values of the same lines would differ so greatly from one another, that I was often very doubtful whether I could rely on any of them, or even on the mean among them all”.
The map he created on which the first contour lines were drawn he describes thus: “… a very large and accurate plan of the whole survey was constructed, forming a map of four feet long by four feet broad, which was verified in every part by the measures of the computed lines…. they were generally found to agree very exactly, according to the scale by which the plan was constructed. The use of this large map was to receive and admit of the distinct and accurate exhibition of the figures in their true places, expressing the number of feet in elevation or depression with respect to each observatory of every point and section of the ground whose elevation or depression might be observed.” From his description I feel sure this original manuscript map would also have shown one of the earliest uses of spot heights. Sadly the map is missing, although with considerable help from Emeritus Professor of Mathematics Robin Johnson, I hope to show an accurately scaled recreation of this first contour map at The Literary and Philosophical Society in June.