Here is another Thames Tunnel picture found in Greenwich Market from another, equally strange perspective (see Underground, Overground peculiar cross section). This plan illustrates nicely the dot-to-dottiness of our chimneys and tunnels walk. The two dots here mark the grand entrance hall and stairwell either side of the river. I like to think of them as chimneys. They are, after all, cylindrical, vertical and the means of ventillating what lies below: a foot tunnel – the line that joins the dots.
Except, of course, that they don’t quite join up. There’s a curious gap at either end. It’s as if the draftsman wanted to present the tunnel in morse, as a giant R (for Rotherhithe?). Morse code was developed in the late 1830s and 1840s, whereas construction of Marc Brunel’s Thames Tunnel began in 1825 and was completed in 1843. The cryptic message can’t have been intentional if the plan was prepared before construction started. Even so, the use of the language of one form of pioneering nineteenth century underwater communication – submarine telegraph cable – to represent another – the world’s first tunnel under a navigable river – feels pleasingly apt.
The next chimneys and tunnels walk will be on Saturday 23 June.