The coffee houses of the eighteenth century were places where ideas were debated, new innovations created and, of course, coffee consumed. What would a modern day equivalent look like?
Bloomsbury Coffee House is in a basement on Tavistock Place. It is ideally located close to a few universities and was busy but not crowded when we arrived one afternoon during the week. There are two large rooms forming the café with several tables and artwork dotted around the room. In the warmer months, there are also a couple of tables outside in the little terraced area by the steps leading down to the basement. Many people inside that day were on laptops (there is free wifi), some were involved in conversation either with each other or through the laptop. Presentations were being discussed, new ideas bounced around. It is possible that sometimes, when thinking about past coffee houses we can be tempted to focus on what has been lost (in terms of conversation and debate) rather than what has been retained in a modern manifestation (such as idea creation and discussion via Skype, from within the coffee house). At the Bloomsbury Coffee House that day I had an espresso (Allpress) and a cinnamon bun while there were also a variety of milks on offer for other espresso based drinks. These were all a significant improvement on the coffee that was served in the establishments of the past.
Each table was individual, some reminding me of old school desks, while the ceiling was plastered with a 2D square lattice pattern. Staring at the ceiling, prompted the question, was it the large squares or the small squares that formed the repeating unit of the structure? Quickly this made me think about Polonium. When thinking about how atoms form 3D crystal structures, we sometimes naively draw a cube with an atom at each corner. In fact, this arrangement (the simple cubic structure) is quite unstable (try stacking oranges on top of each other so they form a cube) and, for elements that do form into cubic crystal structures, a more common form of base unit is a so-called face centred or body centred cubic. One element that does form a simple cubic structure though is polonium, an element that is probably more famous for being the poison used in the Litvinenko case a few years ago.
However, an alternative train of thought was suggested by the blackboard on one of the walls of the room. A colourful message announced that the Bloomsbury Coffee House had won a Time Out Love London award. The writing, in red and blue, was a little tricky to read from the back of the room. With the lighting, the red appeared slightly brighter and more visible than the blue. Perhaps coincidentally, this is the correct way round (in terms of order of brightness) for an odd optical effect that happens as the light fades towards evening (and, in a connected manner, why it is hard to find a matching pair of socks in the dark).
In order to ‘see’, the eye uses a series of cells called rods and cones. The rods are the more light sensitive and more plentiful (there are more than 100 million in a human eye) but they do not have any mechanism to detect colour. Instead, they show a good response over the entire visible range with a peak response rate at ~507 nm¹ which corresponds to a blue wavelength. The cones by contrast give us the ability to discern colour. We have blue, green and red sensitive cones which show responses that peak in the blue, green and red parts of the visible spectrum respectively. The problem with the cones is that they do not respond very well in low level lighting conditions. Hence, during the day, in normal lighting conditions, the cones are active and our eyes (usually) show a peak response to yellow-green light at 555 nm. As the light falls and twilight and darkness comes in, the cones cease to work leaving only the rods so our eye’s peak response shifts to light with a blue wavelength. Subsequently, a bright red rose seen during the day may appear dimmer than the green leaves in the evening. A sea of blue and red flowers may shift from appearing bright red to bright blue as night falls.
Unfortunately, Bloomsbury Coffee House closes at 6pm which, during summer, is too early for us to see whether we can see this effect ourselves. But if you are lucky enough to have access to a garden or park where there are red flowers and are able to sit and watch them as night falls, do observe and see if you can see this shift in apparent brightness for yourself.
Bloomsbury Coffee House is at 20 Tavistock Place, WC1H 9RE
¹The Feynman Lectures on Physics, Vol I