Good vibrations at Rosslyn, Mansion House

Coffee at Rosslyn, Mansion House, EC4N, coffee clock, base
Coffee time at Rosslyn, EC4N. Why is it that base 60 was used as a counting system in Mesopotamia? And why is it that the echoes of this are still seen in our clocks and the angles of a circle (unless you use the radian system) but not in our everyday counting system?

It’s always “coffee time” at Rosslyn apparently, at least according to the clock above the door. In front of you as you enter the cafe is the counter and, as you move down to collect your coffee (for take-away) the day’s edition of the Financial Times is stuck to the notice board where you wait. An interesting touch, somehow making a resonant connection with the City coffee houses of old such as Jonathan’s, just around the corner, where the stock market was originally located.

There are not many stools or tables in Rosslyn, which appears to be designed as more of a take away space. Nonetheless, we found a perch by the window overlooking the bench seats outside. It is a perfect place to watch the world go by. The massive junction of Poultry providing plenty to see.

Coffee is roasted by Modern Standard and there are bags of roasted coffee on sale (together with some of the mugs) at the other end of the counter to the FT. The occasional (welcome) plant reminds us that life is not just concrete, glass and cars/buses. Although it was sunny, it was not yet hot and so we had a soy hot chocolate and a long black, went back to take our seats and waited for the drinks to arrive.

The wooden spoon that came with the coffee was an interesting touch, reminding me of Barn the Spoon and his work in Hackney. While the clock got me thinking about our use of base 10 as a counting system and the older systems that used base 60.

coffee, hot chocolate, plant, mugs, wooden spoon.
A quiet moment with a coffee and a hot chocolate at Rosslyn. Notice the spoon.

Contemplating these things we noticed a strange effect in my coffee. Or rather, I noticed it and brought attention to it by taking repeated photographs of the coffee while tapping the bench just to try to capture what I was seeing: a resonance pattern on the coffee surface. At this point, your mind may connect to several different things. There’s the resonance effects involved in the Whispering Gallery in St Pauls close by to Rosslyn. There are the resonance patterns caused in bells, drums and violins and the relation between these, air movement and music. There’s the fact that these movements initially revealed the excellence of the table as a movement sensor: the ripples on the coffee revealing footsteps behind us rather like we detect earthquakes in the earth. (My later attempts at photographs were in that sense “faked” as I was tapping the table beside the cup to try to reproduce the effect so that it was visible on my camera).

Or there was the fact that this movement in the coffee cup is exactly the same phenomenon as something in our lab. But whereas in the cup it is an interesting, almost aesthetic feature, in the lab it can be a major pain to deal with.

The problem comes in that the coffee cup was in the middle of the bench. This had been an accident in terms of where we were seated but it had large effects. Because the bench table has its legs at each end, but nothing in the middle, the table itself acts as if it is a massive drum. And one of the more fundamental resonances of a drum has the maximum movement at the centre of the drum: the edges don’t move much but that bit in the middle oscillates wildly. In the coffee cup this manifests as a ripple pattern on the coffee surface, reflecting the street outside in slightly distorted fashion. In the lab this means that some of our instruments become incredibly difficult to use.

ripple pattern coffee Rosslyn
Can you see it? The ripple pattern caused by the coffee being on the drum of the table at Rosslyn. An interesting effect to watch in coffee but what if this sort of thing happens in a physics lab?

Consider for example the Atomic Force Microscope (AFM). This microscope is able to resolve the structure of films down to an almost atomic resolution. It does this by monitoring the resonance of a small silicon cantilever as it approaches the surface of the material being studied. Just for a moment, put a wooden sugar stirring stick (or a lollipop stick) on the edge of a table and ‘twang’ it. It vibrates just as the silicon cantilever does in the AFM. Then think, what if you put the stick in honey and ‘twanged’ it – or put a magnet on the end of it and ‘twanged’ it over a bit of iron, how would the oscillation change? This is what the AFM does but with the atomic forces that are present when you get very close to the surface of a sample. But the phrase “very close” is key. Typically, the cantilever will be nanometers from the surface of the sample and, as it is very sensitive to the forces at the surface of the sample, if that sample moves because the instrument is vibrating up and down on the floor, the image will be at best blurry and unusable and at worst, you are going to be damaging your cantilevers.

And so, it is important to ensure that the AFM is placed in a suitable area of the lab: not in the middle of a floor in a high level building because that will just act as a drum in exactly the same way as the coffee cup was being vibrated at Rosslyn. If you’re not fortunate enough to have the AFM in a basement lab, you could place the AFM (and other vibration sensitive instruments) at the corner of the room, so the vibration amplitude of the floor-drum is minimised. You could also try to place the instrument on concrete blocks to ‘damp’ the vibration. An extreme example of this sort of damping is the ‘quiet labs’ of Lancaster University just next to the M6 motorway. These labs have been designed to minimise vibration noise and the team there routinely achieve atomic level resolution with their atomic force microscopes.

The silence of an area next to the M6 contrasting with the noise of the City. The directions that contemplating a cup of coffee takes you are always surprising.

Rosslyn is at 78 Queen Victoria Street, EC4N 4SJ

Coffee Damping

vortices in coffee

Vortices behind a tea spoon

How often do you allow yourself to get bored? Or to sit in a cafe and take your time to enjoy your coffee properly, noticing its appearance, the smell ‘landscape’ of the cafe, pausing while you absorb the sounds of the cafe and playing with the feel of the coffee while you create vortices with your tea spoon?

If you regularly drink black coffee, you may have noticed how these vortices form more easily in the coffee once the crema has dispersed. Intuitively this may seem obvious to you, perhaps you wouldn’t even bother trying to form these vortices in a cappuccino, you’d know that they wouldn’t appear. The bubbles of the crema (or the milk in the cappuccino) quickly kill any vortex that forms behind the tea spoon (we’d technically call it ‘damping’ them). But even when we are aware of this, it is still surprising just how quickly the crema stops those vortices. Try forming a couple of vortices in a region of black coffee close to a region of crema. Indeed I thoroughly recommend ordering a good black coffee in a great cafe somewhere and just sitting playing with these vortices all the while noticing how their behaviour changes as the crema disperses.

latte art, flat white art

Latte art at The Corner One. Lovely to look at but not good for the vortices.

The damping caused by bubbles on the surface of a coffee is responsible for another phenomenon that you may have encountered in a cafe but, to be fair, are more likely to have noticed in a pub. Have you ever noticed that you are less likely to spill your cappuccino between the bar and your seat than you are your lovingly prepared filter coffee? Or perhaps, in the pub, you can get your pint of Guinness back to the table more easily than your cup of tea? (At least for the first pint of Guinness)

Back in 2014, a team investigated the damping properties of foam by controlling the size and number of bubbles on top of a liquid as it was vibrated (sloshed) about. They found that just five layers of bubbles on top of the liquid was enough to significantly damp the liquid movement as it vibrated from side to side. That is, five layers of bubbles suppressed the sloshing (try saying that after a couple of pints of Guinness). Much as I dislike emphasising the utility of a piece of science, this work has obvious implications for any application that requires the transportation of liquids such as the transport of oil containers. There is an obvious need to suppress the effect of liquid oil sloshing from side to side as it is transported by boat for example.

The foam on our latte or crema on our long black should indeed give us pause for thought as we sit in a cafe enjoying our coffee.