Newton

Looking at coffee

coffee at Watch House
Observing the colours in our coffee can reveal much more than just the chemistry of the cup.

How do you see your coffee in the morning? Through blurry eyes, a red-ish/brown liquid that you may admit to noticing more for its aroma and taste than for how you look at it? But what is it about that lovely red colour of a fresh filter coffee viewed through sunlight? And what about the way that the glass jar curves towards you and then bends away, how do we perceive distance?

The colour question has historically been more problematic. For Aristotle, the rainbow was composed of a mix of three colours, which fitted with Pythagorean numerology*. Newton thought there were seven, which fitted with the harmonies in music theory. Goethe (who also developed a colour theory) liked to quote “If you show a red rag to a bull it becomes angry, but a philosopher begins to rage as soon as you merely speak of colour”**.

Today, in schools we are taught that there are three primary colours for light: red, green and blue. This is because all colours of light can be observed by careful weightings of these three colours and when the three are combined we see white light. But what does it mean that light has primary colours? Is not light just a vibration, why is it that we see colour at all? It comes down to our physiology and how we sense the world.

It was Thomas Young (who also showed the wave-like properties of light) who first proposed that these three ‘fundamental’ colours were associated with three types of ‘resonator’ in our eyes. The idea was significantly developed by Hermann Helmholtz during the 1850s. Each type of receptor responded to light at all frequencies but responded most sensitively in a smaller range. Generally humans have three types of frequency sensitive (and so colour sensitive) receptors, though those with colour blindness have fewer and there are even some of us with four. Most of us though, have three types of receptors sensitive in the red, blue and green regions of the spectrum. Hence we perceive the light as white if these three types of receptor are stimulated equally, that is, if we combine blue, red and green light. The red colour seen as you brew a fresh pour over of coffee in front of a window through which sun is streaming at dawn, is red because of these activated red-sensitive cone receptors in your eye.

Sun-dog, Sun dog
A ‘rainbow’ of colour as seen in a ‘sun dog’ observed in central London. But what is colour really?

But Helmholtz went further than this. Have you ever been staring at a bright object and then turned away towards a dark wall and had the experience of seeing the same bright object ‘projected’ on the wall but in a different colour? Both Goethe and Helmholtz observed themselves as they ‘saw’ these phantom images and watched the images as they changed colour before eventually fading. While Goethe incorporated his observations into his general colour theory, Helmholtz linked the phenomenon to these same cone receptors in the eye. He realised that if your red-sensitive colour receptors had become saturated by watching a bright red object (such as a red-hot piece of iron for example), they would not respond so quickly when you looked away at a blank bit of wall. So if you, for example, ordinarily perceived the wall as white, because the red-colour receptors had been taken out for a while, your blue and green receptors would dominate while the red would not respond and so cause you to observe a greener phantom image. Would we ever see a green phantom coffee?

Unlike the question of the colour, the question of depth perception has some thoroughly more modern elements. For while many had thought about how we realise that space has depth, the binocular effect of our two eyes was not realised until relatively recently. In fact, that two, 2D images taken from slightly different angles and viewed separately through each eye appeared as if they were a 3D image, was only discovered in 1838. Prior to that, it had been thought that perhaps we knew about depth because of our learned familiarity with the size of objects, much as Fr Ted explained the distant cows to Dougal (which is one of the clips here).

Shadows reveal a lot. From the position of the light source to information we interpret as informing us about how different objects relate to each other. And again, why is it that shadows appear blue on snow?

Apparently between 1855-59, 29% of scientific papers concerning the eyes were about this problem of stereoscopy or binocular vision. Helmholtz’s contribution to the debate was to show how much of our realisation of depth was a learned but unconscious process and also how much relied on the involuntary movement of our eyes to ‘calibrate’ the surroundings after fixing on something. That movement of your eye that is impossible to control but you can watch in others as they concentrate is there for us to check that what we think we are seeing is what we are seeing.

Just how much is revealed to us, about the coffee and ourselves, by our gazing at it? When Feynman discussed colour vision in volume I of his Lectures on Physics, he wrote “We make no apologies for making these excursions into other fields, because the separation of fields… is merely a human convenience, and an unnatural thing. Nature is not interested in our separations, and many of the interesting phenomena bridge the gaps between fields.”*** Our world is intricately connected, we only have to gaze at our coffee to have an intuition as to how much this is true.

This post is one of a series about the contributions of Hermann von Helmholtz to how we understand the world around us. The introduction is here and it will be followed by thinking about what we hear in our coffee, the heat of our coffee and, of course, what happens when we stir it.

*”The Rainbow Bridge: rainbows in art, myth and science” R.L. Lee Jr, A.B. Fraser, Penn State University Press (2001)

**”Helmholtz: from enlightenment to neuroscience” M. Meulders, MIT press, (2010)

***”The Feynman lectures on physics volume I”, Feynman, Leighton and Sands.

Hidden appearances at HoM

hot chocolate, soya, marsh mallow, HoM

Hot chocolate with marshmallows at HOM, Kings Cross.

In these long dark afternoons in the northern hemisphere, what could be better than a warming mug of lovely coffee in a bright environment? And so it was that we ended up at House of Morocco (HoM) on the Caledonian Road. Alerted by Brian’s Coffee Spot that Pattern Coffee had changed hands and become HoM we headed up to Kings Cross one damp afternoon in December to see how things had changed. Entering HoM is a strange mix of déjà-vu mixed with new. The pattern on the wall next to the window remains, as does the layout of the place. However it is also clear that much has changed since HoM took over.

There are murals and variously coloured cushions dotted around the café. Even in the darkness of the afternoon, the café was bright, but also crowded. We ordered a soya hot chocolate, a long black and a cheesecake and found a seat perched at a small table for two near the door (the only seat left at the time). The coffee, roasted by Terrone Coffee, was nicely balanced for the afternoon. But it seems that the hot chocolate and cheesecake combination were a real hit. The cheesecake was apparently very good (definitely worth a return visit apparently) while the hot chocolate went very quickly!

Inside the café, the windows were steaming up with the warmth of the inside. We over-heard that this was because of the coffee machine rather than any extra heating that had been installed. Does this suggest an alternative energy source? Coffee machine heaters to go with treadmill electricity generators in gyms?

all about pigmentation at HOM

Menu with sugar bowl and glazed tile at HOM, Kings Cross.

Meanwhile, the decoration was demanding my attention. A vividly coloured glazed tile supported a jar of sugar which was propping up a black and white menu. The menu had an illustration reminiscent of henna tattoos while above all of this balanced a peacock feather in a vase. Underneath the peacock feather was a poster advertising the “Phantom of the Opera”. The whole ensemble was suggestive of appearances and how they can be deceptive. The phantom of course wore a mask to disguise his disfigured face. But the peacock? The peacock is hiding something too.

Many of the colours that we see around us such as those making our coffee brown and making the tiles colourful are as a result of energy from the light being absorbed by the atoms in the substance (the coffee or the tile). This type of light absorption (and emission) can be connected with vortices in coffee as was discussed here. However the blues and greens in a peacock feather are different. If you look at the feather under a high powered microscope, you will find that the feathers are not dyed as such, in fact the natural colour of the feathers is quite dull. Made from keratin (as you can find in your fingernails) and melanin (responsible for the brown pigmentation of your skin, eyes and hair), the feathers do not seem blue at all. In fact it is the structure in the feather that is producing the colour rather than any dye that produces the colouration.

It turns out that there is a long history concerning our understanding of the colours of a peacock’s feather. It started with Robert Hooke who, in 1665 described the feathers of both peacocks and ducks and noticed that the colours he saw under an optical microscope were ‘destroyed’ by putting a drop of water on the feather. A little bit later and Isaac Newton was suggesting that the colouration was due to the thickness of the transparent bits of the feather. There’s a link here to coffee. Newton was suggesting that an effect similar to thin film interference (which causes the rainbow colours on the bubbles in a coffee) was causing the colours of the peacock feather.

appearances at HoM

Peacock feather and phantom poster with the top of a mirror. How does structure affect what is seen?

As our understanding developed through the centuries (and the microscopes became more powerful), it became apparent that while thin film interference (and multiple film interference) could cause some animals to appear as if they had certain colours, the peacock, along with some other animals, was a little bit more special. Rather than just being the result of reflection off an interface, the peacock’s feathers showed structure at the nanoscale (1/1000000 of a mm). The keratin and melanin in the feathers were arranged in a square lattice to form what is known as a ‘photonic’ crystal. The way this structure reacted with incoming light meant that only certain wavelengths were reflected from it. Depending on the size of the layering in the feathers, they appeared as blue, green or yellow.

Although a lot more is now understood about the factors, structural and chemical, that lead to colouration in all sorts of creature, be they butterflies or beetles, peacocks or pigeons, there is still more to discover, more to understand. The authors of the paper referenced here wrote

“In this paper, we describe a wide variety of structural colors occurring in nature and attempt to clarify their underlying physics, although many of them are not fully clarified.”

There’s clearly a lot more work to do before we can properly explain these “beautiful microstructures”.  And plenty of time to do so as we sit enjoying well made coffee and hot chocolate in a bright and warming café.

HOM can be found at 82 Caledonian Road, N1 9DN

 

Light and gravity at Tab x Tab, Westbourne Grove

drinks in ceramic mugs, Westbourne Grove

A soya hot chocolate and my black coffee at Tab x Tab

Earlier this summer, a new café opening on Westbourne Grove attracted a lot of attention. “Tab x Tab” quickly received reviews from Brian’s Coffee Spot (who noted the unusual espresso machine), Bean There at and Doubleskinnymacchiato. Bean There at also suggested that there should be plenty to ponder at Tab x Tab when I finally got the chance to get there. And so, a trip to this café had been on the agenda for a fair while.

Wandering into the café, it seemed exactly as described by the reviews: clean, sharp interiors in a modern building. It was fairly crowded when we arrived just after lunch and so we ordered before taking a seat at the bar (two of the few seats left). I had a long black while my fellow imbiber had a soya hot chocolate. The drinks arrived in those distinctive mugs mentioned by doubleskinnymacchiato (and pictured above). As we had just had lunch, on this occasion we didn’t check the edibles on offer but with plenty of other reviews of the coffee and the cake, I’m sure that you’ll find recommendations there (I understand the avocado on toast with cashew nut is well worth trying).

Graphite, double layer graphene, stacked hexagons

Plant on two slates at Tab x Tab, Westbourne Grove

Sitting down to enjoy our drinks, the first thing to notice was that Bean There at was absolutely right. Despite the slightly minimal and elegant decoration, there were plenty of things dotted around that were slightly quirky. Firstly there was the plant that had been placed on two hexagons of slate that had been ever so slightly displaced from each other, presumably for aesthetic effect. Could this link to graphene and graphite with their strong intra-layer bonding and weak interlayer bonding (so the hexagons of carbon in graphite slide over each other)?

Then there was the selection of items for sale that also provided food for thought. Books and other items from the School of Life, something to think about as you stop with your coffee perhaps. In the other direction, on the counter top, a couple of Venus Fly Traps were waiting for their lunch. There is so much we have yet to learn about the symbiotic relationships between plants and animals and especially between plants and fungi. As we looked further around the café, there was something else a little odd. Just as the name “Tab” was written both the correct way and upside down in the window, so the plants in the hanging baskets were hanging upside down.

which will win, gravity or light

Plants hanging upside down in the window at Tab x Tab

This seemed a bit strange in itself. Plants have a tendency to move upwards towards the light. This behaviour of plants (and trees in particular) provides one way to identify which way is south when walking in the country without a compass¹. It is odd to see a plant growing downwards and suggests that the plants in the window are regularly rotated so that they don’t try to reach up. As Simone Weil wrote “Two forces rule the universe: light and gravity”². Which would win in the end? To be fair, Weil was not referring to the light that streamed through the windows in Tab x Tab giving the plants the force they need to move upwards. Nonetheless, whether one is thinking literally or analogously, it is an interesting question what pulls us down, what brings us up?

There is a story that Newton arrived upon his idea of universal gravitation by contemplating a falling apple. Considering that the plants were approximately 2m above the floor level, and using the fact that the acceleration due to gravity, g,  is 10 m/s², if the plants were to fall from their hanging position, they would take:

s = ½gt²

t = 0.6 seconds

to fall and smash to the ground*. While this brings to mind Newton’s experiments dropping pigs bladders filled with liquid mercury from the dome of St Paul’s Cathedral, it is worth instead thinking more about the universal nature of the gravitational force. This is of course what made Newton’s idea of gravity different from the theories that had preceded it. People had known that if an apple fell from a tree (or a plant fell from its hanging basket) it would fall to Earth. What was key to Newton’s idea was that what applied to the apple, applied to all other masses too. The same maths that could be used to calculate how fast a plant dropped, could be applied to the Moon. So, if this was the case, could we calculate the orbital distance of the Moon in the time it took us to enjoy a coffee at Tab x Tab? We know that the Moon’s orbital period is τ = 27.3 days (2.36 x 10^6 seconds) so assuming that the gravitational force acting on the Moon is balanced by the centripetal force, we can equate the two:

Gravity: F = GMm/r²

Centripetal: F = mv²/r

Where, G is the gravitational constant (6.67 x 10^11 Nm²/kg²), M is the mass of the Earth (5.97 x 10^24 Kg), m is the mass of the Moon and r the moon’s orbital distance (which is what we want to calculate). If we assume that the Moon travels in a circular orbit (not quite true but not a bad first approximation), then we know the speed, v, of the moon in terms of the orbit period, it is just:

v = 2πr/τ

A bit of re-arrangement and some plugging in of values leads to a back-of-the-envelope value for the Moon’s orbital distance of 383 000 Km. A value that does not compare badly at all with the average distance of the Moon given by NASA as 384 400 Km.

Perhaps if we’d stayed for an additional flat white we could have refined the calculation somewhat and so obtained a value closer to reality. Nevertheless, the fact that the force that is pulling the plant down at Tab x Tab is the same as is pulling the Moon around the Earth, and that we can quickly check this (and get an approximately correct answer to our calculation), is one of those ‘wow’ moments in physics. Realising the universality, and elegance, of certain mathematical relations. So perhaps it is entirely appropriate that this thought train of mathematical elegance was prompted by the quirky but aesthetic elegance you will find at Tab x Tab.

Tab Tab can be found at 14-16 Westbourne Grove, W2 5RH

¹ The Walker’s Guide to Outdoor Clues & Signs, Tristan Gooley, Hodder & Stoughton, 2014

² Gravity and Grace, Simone Weil, Routledge (1995 vsn)

*Although you could use a more accurate value for g, the error on the estimate of the height of the plants makes such precision potentially misleading. The value 0.6 seconds is absolutely a back-of-the-envelope, calculation.

Ghosts of Christmas Past, the Devereux

Grecian, Coffee House, London Coffee House

The Devereux now stands where the Grecian once was

The Grecian is steeped in history. One of London’s early Coffee Houses, it counted Isaac Newton and Edmond Halley among its regulars. Today it is the site of a pub, “The Devereux“, owned by Taylor-Walker. The building itself dates from the nineteenth century though it is on the site of the old Grecian (a drawing of which can be seen on a wall inside the pub). In a sense, the Devereux is a continuation of the Grecian that once existed on this spot and it is for this reason that I’ve wanted to enjoy a drink at the Devereux/Grecian for a long time. What better time to do it than for a Christmas themed cafe-physics review?

The Devereux itself is a fairly spacious, comfortable pub, tucked down a little alley just off Fleet Street. It is strange to consider (while sipping on a glass of the 1730 pale ale) that it was here, just over 300 years ago, that the Grecian would host the after-meeting “pub outing” of the (then newly formed) Royal Society. Paintings and photographs of the Grecian and the Fleet St. area surround you, as you sit and enjoy your drink (they do serve tea and coffee too). Indeed, it is possible to almost feel the history of this place. I recalled reading a 1686 paper in the Philosophical Transactions by Edmund Halley in which he described a live demonstration, in front of a meeting of the Royal Society, of just how much water could evaporate from a heated plate of water in two hours. Halley was interested in this as part of the whole question of how rivers formed and where rain came from. I wondered whether Halley and his friends Newton and Sloane, retired to the Grecian after that meeting and sipped on hot coffee as they sat next to the cold windows which started to steam up on the inside.

Vegetable Lamb, Lamb of Tartary

The Vegetable Lamb in the collection of The Garden Museum

Reading about these early frequenters of this drinking establishment, it is hard to avoid the impression that they were driven by an interest in knowledge and knowing things. Of course the term ‘scientist’ had not yet been invented*. Science as in ‘scientia’ was still just Latin for knowledge, the men who gathered at the Grecian (and they were mostly men) were not “scientists” they were Natural Philosophers. Hans Sloane, another regular, was a great collector, finding curiosities from around the world and displaying them in his house. Most of his collection became the start of the British Museum but there is one curiosity of Sloane’s that I came across recently that is not to be found there at all and that is his “Vegetable Lamb”.

Vegetable Lambs were believed, in the seventeenth century to be, genuinely, part vegetable part animal. You can see from the photo that they do look fairly animal-like. According to the Garden Museum, these vegetable lambs originated in the Far East but now only two remain in the UK. The one that belonged to Hans Sloane (which is in the Natural History Museum) and the one that belonged to John Tradescant and that can now be found in the Garden Museum (now sadly closed until refurbishment is complete in 2017). Hans Sloane’s contribution was to show that this vege-animal was in fact purely a plant, a type of fern, which may make vegetarians everywhere breathe a sigh of relief. It was because these people were interested that they worked so hard in trying to understand the world around them. Which brings us, somewhat surprisingly, to one of the more recent famous patrons of what had by that time become, the Devereux.

Chesterton

The festive Chesterton bookshelf at the Devereux

GK Chesterton is not known for his scientific research. However, he did spend a great deal of time thinking and writing about all sorts of things. (It also appears that he spent a fair amount of time in the Devereux where there is an entire bookshelf of his books). A book of Chesterton’s essays “As I was saying” was published in the year of his death, 1936. Within that book is an essay “About the Telephone”. Chesterton was musing on a sentence that he had read in a newspaper that had troubled him: “The time will come when communicating with the remote stars will seem to us as ordinary as answering the telephone”. Chesterton wrote “Now if you could say to me: ‘The time will come when answering the telephone will seem to us as extraordinary as communicating with the remote stars…’ then I should admit that you were a real, hearty, hopeful, encouraging progressive.” I suspect that with our tendency today towards the fragmentation of knowledge and increasing specialisation, we would categorise the work of Newton and Halley, Sloane and then Chesterton in quite different compartments. Yet it seems to me that they share something in their work: an element of wonder and curiosity at the world. As Chesterton continued in “About The Telephone”,  I am not objecting to the statement that the science of the modern world is wonderful; I am objecting to the modern world because it does not wonder at it.

It sometimes seems hard for us to sit in a cafe on our own without using, or at least looking at, our telephones. Checking our email or the latest news on our telephones has become extraordinarily ordinary for us. Maybe this should be our New Year’s resolution: put our phone back into our pocket and consider, with Chesterton, Sloane, Halley and Newton, just how wonderful it is.

Happy Christmas & New Year to all

 

* The word science/scientist was first used in the sense that we now understand it by William Whewell in the nineteenth century.

“As I was Saying – a book of Essays by GK Chesterton” was published by Methuen&Co Ltd, 1936

The Devereux can be found in Devereux Court, just off Fleet Street, WC2R 3JJ

Gravity and Grace at the Wren cafe

Wren cafe, St Nicholas Cole Abbey

Inside the Wren cafe

There is a lot to like about the Wren cafe. Firstly, there is the space that it occupies (inside St Nicholas Cole Abbey). I went at lunchtime when the way that the light came through the stained glass windows made the cafe a very relaxing and open space. The coffee is from Workshop, complementary water came in 3 flavours (mint, cucumber or lemon) while the food is cooked on site. This is important because it means that they have a great nut policy and could tell me which dishes were likely to contain nuts etc. A further nice feature of the lunch menu at the Wren was that you could select your portion size. Food waste is a major issue for our society and is not helped by the ‘one size’ portions served at many food outlets and cafes. Lunch was offered in two sizes (technically as a side or a main) but the ‘side’ was more than adequate for a mid-week lunch. Sofas in the corner of the room meant that you could relax and take in your surroundings in a comfy environment or, if you were just there for lunch, ordinary chairs and tables were dotted around the room.

Of course, a place such as this will have plenty of things to notice about it. Whether your interest is in architecture or science, there is plenty to observe around you. What I would like to focus on though is a bit of science history that connects the name of this cafe with Isaac Newton, John Theophilus Desaguliers and the dome of St Paul’s Cathedral (which you can see from the front of St. Nicholas Cole Abbey).

View of the Dome from the cafe

The Dome of St Paul’s, visible from the side of the Wren cafe.

Perhaps we all remember the story told to us at school about how Galileo dropped two balls of different mass from the top of the leaning tower of Pisa. According to the story, the balls fell to the earth at the same time, thereby showing that the acceleration due to gravity was independent of the mass of the object and paving the way for Newton’s theory of gravity. Sadly, it seems that Galileo may never have actually performed the experiment (even if it was “re-created” in 2009). However there is evidence that Isaac Newton did perform exactly this experiment in 1710 from the dome of the soon-to-be-completed St Paul’s Cathedral.

“From the top of St Paul’s church in London in June 1710 there were let fall together two glass globes, one full of quick silver [mercury], the other of air”¹. The globes fell 67m before shattering onto the cathedral floor (I’d hate to have written the risk assessment for that experiment). To avoid the possibility of human error, a trap-door mechanism had been designed to ensure that both globes dropped simultaneously. According to the story of Galileo told to us at school, we can calculate how long it would have taken those globes to drop to the floor: 3.7 seconds, independent of mass. So is this what Newton observed? No! The heavy glass globes took 4 seconds to fall, but lighter ones took 8-8.5 seconds! A few years later and Desaguliers repeated the experiment from slightly higher in the dome (but this time with hog’s bladders rather than glass) and obtained the same result.

View of St Paul's Cathedral London

Another view of St Paul’s. Hard to believe that Newton actually dropped liquid mercury from the dome.

This surprising result can be explained when we realise that Newton was investigating not gravity, but air resistance. While the gravitational acceleration is independent of mass, the upwards force due to the air resistance depends primarily on the object’s size (and velocity). This means that the deceleration caused by the air resistance will be different for two globes of the same size but different mass (Force = mass x acceleration). Heavy objects will fall faster in air (until the objects reach their terminal velocity).

There is a certain irony in the fact that this result is opposite to what we feel should happen based on what we learned at school of Galileo’s experiments challenging the scientific orthodoxy of the time. However the result of Newton and Desaguliers’ experiments do not contradict the theory of Newton or Galileo, they just add an extra layer to the problem. We do not exist in a vacuum, we need to think about the air around us too.

Both Newton and Desaguliers were regular coffee drinkers albeit at different coffee houses. Desaguliers frequented the Bedford Coffee House in the north east corner of Covent Garden while Newton regularly retired to the Grecian in Devereux Court (just off Fleet Street). Coffee houses were places that the latest science, politics or philosophy were discussed and debated. The Wren describes itself on its website as existing to “serve the ministry of St Nick’s talks“. Sadly I experienced no discussion or debate on my visit (just a very nice, but solitary, lunch and good coffee) but it is interesting to see the tradition of the 17-18th century coffee houses continued in this Wren designed church and cafe.

The Wren cafe can be found inside St Nicholas Cole Abbey, 114 Queen Victoria St. EC4V 7BJ

[1] The Dawn of Fluid Dynamics, Michael Eckert, Wiley-VCH (2006)

Coffee house info: London Coffee Houses by Bryant Lillywhite (pub. 1963)

Bridging worlds at White Mulberries, St Katherine’s Docks

chalkboard at White Mulberries

Sign board at White Mulberries.

Five minutes walk from the Tower of London is an area that feels far removed, physically and metaphorically, from the crowds swarming around the central tourist sights. St Katherine’s Docks offer a peaceful retreat a stone’s throw away from the bustle of the Tower. And if you are in this area, there is no better place to have a coffee (and potentially a cake) than White Mulberries. This café looks over the central basin of the three docks in St Katherine’s and is, seemingly, in the only 19th century warehouse still standing in the docks. On each occasion I have visited White Mulberries the coffee has been very good. As a black coffee drinker, the taste of the coffee has to be great as there is no hiding a bitter espresso with the milk of a latte and White Mulberries has passed every time (their website says that they rotate the coffee roasters, so I can only assume that they have a great relationship with their suppliers). If Latte Art is your thing though, White Mulberries also has that. It was an example of the latte art at White Mulberries that accompanied my recent article in Physics World.

Bascule Bridge, St Katherine's Docks

A moving bridge at the entrance to St Katherine’s Docks. There are youtube videos of this opening.

The point of a “café-physics” review on Bean Thinking though is only partly about the great coffee on offer (all cafes that are featured in the Daily Grind have great coffee). Part of the point of a café-physics review is to look around, slow down and notice things and see what physics there is around the café in question. There is always something to notice, always something science-like to appreciate. White Mulberries is no different, with an enormous number of things to notice, from the water in the docks to the Aeolian harps made by the rigging on the yachts moored nearby. What I would like to concentrate on today though are the bridges. Bridges are often used in scientific outreach with children. I think it is partly because so many concepts in physics can be communicated by practising making bridges. Forces need to be balanced (Newton), stress and strain needs to be considered, the properties of materials are unconsciously learned. And this, I think is another reason that bridges are a great ‘outreach’ tool, because bridges are inherently multidisciplinary. To make a good bridge requires elements from physics, chemistry, mechanical and civil engineering and art to name just a few. A bridge needs to satisfy the aesthetic demands of the public that use it as well as the structural demands of the people that will stand on it. And the bridges in the docks required yet more work and more understanding, for these aren’t just bridges that span a waterway, these bridges need to move somehow to allow boats to pass, either by having a platform that rises up (as with the nearby Tower Bridge), or platforms that swing around (which was the design of some of the original bridges at St Katherine’s Docks). Great thought and understanding went into the design and building of these mechanisms for moving the bridges. There is much to be gained by contemplating bridge design.

Microcord image of Tower Bridge with tourist in foreground

Tower Bridge, Photo © Artemisworks Photography, http://www.artemisworks.plus.com

Which brings us to another bridge, this time a metaphorical one between White Mulberries and the Coffee Houses of the past. The designer of St Katherine’s Docks was Thomas Telford (1757-1834). As well as specifying the design of the docks, he was responsible for some of the original bridges in the docks themselves, particularly a swing bridge that was built in 1828. St Katherine’s Docks was Telford’s only London project but that didn’t stop him from being a regular in a Coffee House near (what is now) Trafalgar Square. For many years Telford drank coffee in the Salopian Coffee House (most likely in Spring Gardens, just behind Cockspur St). This was where he stayed when in London and, as he was a famous engineer by that point, he started to attract crowds of engineers and admirers to the Salopian in the hope of meeting him. So important was Telford to the business of this central London coffee house that, when he left to live in Abingdon St, the new landlord of the Salopian complained to him “What, leave the house? Why sir, I have just paid £750 for you!”.

Fortunately, White Mulberries has far more to attract customers to it than one illustrious coffee drinker, though perhaps it has those as well.

 

White Mulberries is at St Katherine’s Docks, E1W 1AT,

A good book on bridges is: “Bridges – the science and art of the world’s most inspiring structures”, David Blockley, Oxford University Press (2010)

Coffee House anecdotes from “London Coffee Houses”, Bryant Lillywhite (1963)

Arepa and Co, Haggerston

Haggerston Canal

Arepa and Co are on the right hand side of this canal

Edmond Halley (of comet fame) was born in the London district of Haggerston in 1656. More recently, Arepa and Co a Venezuelan cafe located alongside the canal that runs through the district, has just celebrated its first birthday there. This cafe serves a variety of Venezuelan foods including the arepas of the name which are, apparently, a traditional corn cake that can be filled with a variety of fillings (more info here). There are seats both inside the cafe or outside, overlooking the canal. As it was the early afternoon and we’d already had lunch, we decided upon a coffee, a sugar cane lemonade and, to accompany it a plate of Tequenos de Chocolate. These unusual little pancakes filled with chocolate were delightful to enjoy with a cup of coffee and a view over the canal. Sitting back and enjoying this relaxing view, I noticed a tree on the roof of a building on the opposite side of the canal. Hanging on the tree were a number of glass shapes. As the wind blew, the different faces of the shapes caught the Sun. Looking towards these glass shapes, they appeared to change colour as the sunlight was refracted through them. A glinting rainbow array of light fell onto our side of the canal.

The story of the investigation of colour is a great example of how our preconceived ideas can influence the results that we think we see. Up until the seventeenth century, colour was viewed as a property of the surfaces of an object as opposed to “light” which was that which rendered objects visible. Therefore trying to explain how rainbows formed or light scattered from ornaments was a difficult task. Indeed, medieval philosophers (the term ‘scientist’ is a nineteenth century invention), considered that there were only seven colours: Yellow, orange, red, purple, green and black and white.

Prism associated with Isaac Newton

A late C17th prism in the British Museum collection, © Trustees of the British Museum

Work understanding colour as a refracted component of white light started with Marci in his 1648 work Thaumantias (another name for Iris, the Greek goddess of the rainbow) and continued with Newton’s famous experiments with prisms. Newton showed that a glass prism refracted the different colours of light by different amounts (resulting in a spectrum). If two prisms were placed at right angles to each other, the rainbow of light from the first prism recombined into white light emerging from the second. With the change in mindset that this brought about, phenomena such as the rainbow could be more easily explained.

Grecian, Coffee House, London Coffee House

The Devereux pub now stands on the site of the Grecian coffee house, a former meeting place of the Royal Society

Which brings me back to coffee. Back in the eighteenth century cafes (or coffee houses) were not just places to have coffee but places to engage in the latest philosophical, political or scientific discussion and debate. Scientists of the day regularly gave public lectures and demonstrations in coffee houses both as a way of entertainment and of education. One scientist who participated in this was Stephen Demainbray (1710-1782). Demainbray demonstrated Newton’s experiments and theories on colour to a coffee drinking audience. The models that he used to explain the refraction of light are now on display in the Science Museum which is well worth a visit if you are in London. In the present day, there are still cafes and coffee houses that try to do a similar thing (of showing fun science to a coffee drinking audience), although perhaps sadly there are fewer now than there were then. Two movements that are trying to put the science back into coffee houses are Science Cafes and Cafe Scientifique. Although not always held in cafes, both movements have the aim of combining interesting science with a cup of coffee or glass of wine. Somewhat poetically the next Cafe Scientifique in London is to be held, on the 9th December, at the Royal Society. It is poetic because back in the time of Newton, discussions with the Royal Society president (Newton) and other society members took place at the Grecian Coffee House.

Both “Science Cafes” and “Cafe Scientifique” have events worldwide. It is worth taking a look at their websites to see if there is an event near you. Why not pop along and see what you can find out while having a cup of coffee?

 

Sources used:

The Rainbow Bridge, Raymond L Lee, Jr and Alistair B Fraser, Pennsylvania State University Press, 2002

The Nature of Light, Vasco Ronchi, Heinemann, 1970

London Coffee Houses, Bryant Lillywhite, George Allen & Unwin Ltd, 1963

From a Caravan to the Grecian

It is a Saturday morning as I write this while sitting in Granary Square in Kings Cross, London. I’ve just enjoyed an Ethiopean filter coffee at Caravan. If only more cafes offered the possibility of sampling single estate coffees rather than the espressos that are otherwise so popular in London.

Caravan, Granary Square, coffee, single estate, good cafes in London

The fountains in front of Caravan

In the square outside, people are laughing (and dancing!) in front of the old warehouses that accomodate Caravan. Amongst them all, four sets of ground-level fountains push jets of foaming water 50cm into the air, in patterns that change as you watch. There is so much physics here to observe: The white colour of the water foam, the dance of the water droplets as they emerge from the main jet of the fountain and then fall back to earth, the fact that the wet concrete around the fountains is darker than the dry concrete nearby.

Consider though one more observation. As the water shoots upwards, it is pushed by occasional gusts of wind from west to east making the fountains appear as loops rather than columns of dancing liquid. Although the direction of the wind is determined by local weather patterns, over the UK the prevailing wind direction is Westerly, that is flowing from west to east.

People have wondered about the origin of the winds from ancient times. The Greeks had four wind Gods who had authority over the winds from each direction: Boreas, god of the North wind, Notus of the South, Euros of the East and Zephryos of the West. Pliny the Elder speculated at length on the causes of the winds and yet the start of the modern conversation regarding the origin of the winds had to wait until 1686 with the publication of a work by Edmund Halley.

Grecian, Coffee House, London Coffee House

The Devereux now stands where the Grecian once was

Halley (1656-1742) is now more famous for the comet that is named after him rather than his meteorological work but, as with many scientists of the time, he had his finger in many pies. He also seems to have been a keen coffee drinker, or at least, he regularly spent time in one of London’s coffee houses, the Grecian, discussing science with Isaac Newton, Hans Sloane and others. A pub, the Devereux, now stands on the site of the old Grecian in a little side street off of Fleet Street.

Did Halley ponder cloud formation, rain and the origin of the winds while contemplating his steaming coffee cup on cold days in 17th Century London? Regardless, Halley did recognise that the heat from the Sun was the driving force for the wind system. Halley surmised that as a parcel of air was heated by the Sun and rose upwards, the cold air surrounding it would have to flow in to its place so as to replace the risen air so “..by a kind of Circulation N.E. Trade Winds below will be attended by a S.W. above, and the S.E. with a N.W. Wind above”* The problem for Halley was that his explanation of the wind system could account for a North-South wind direction owing to the Sun’s heating the air at the equator, but not the Easterly direction of the Trade Winds near the equator nor the Westerly direction of the winds over the UK.

A few years later, George Hadley (1685-1768) suggested that it was the rotation of the earth that was responsible for the east-west component; the mass of air, being detached from the earth, would appear to flow in a particular direction as a consequence of the earth spinning below it. The idea was not new, Galileo had proposed it some years earlier while similar arguments were made later by the philosopher (and scientist) Immanuel Kant (1724-1804). At first sight, such an argument looks appealing but there are problems, as John Herschel (1792-1871) pointed out. If this were the explanation for the wind direction, the effect would be “so great as to produce not merely a wind, but a tempest of the most destructive violence”.

Herschel suggested, as had Hadley before him, that friction could slow the wind to the speeds that we normally observe, but while this may explain the wind speed at ground level, what about the upper circulatory patterns noted by Halley: What friction could slow these down?

Grecian, Devereux, Coffee house London

A plaque outside the Devereux pub

It turns out that this is not the reason for the discrepancy in the wind speed. Hadley’s theory was wrong on a number of issues (if you are interested, I suggest reading this article). The real driving force for the Trade Winds is the Coriolis effect which deflects the warm air rising at the equator towards the right as it travels to the North pole. The majority of this air then cools and descends at about 30 degrees latitude, circling back on itself (as per Halley) as the Easterly trade winds. However the air that continues in the westerly direction north (or south) of 30 degrees latitude becomes those prevailing westerlies of the sort that batter the shores of the UK (see here for more information).

Even if Hadley’s simple model was wrong, its contemplation did lead to an important discovery that is still relevant for us today. The question was: What was it in the upper atmosphere that could cause a friction effect that could slow the winds? The person contemplating this question was taking a walking holiday in the Alps in the first half of September in 1886. Hermann von Helmholtz (1821-1894) observed a layer of clouds which showed “whirls formed by perturbation and rolling up” of the surfaces of two neighbouring layers of air. Helmholtz had observed what became known as “Kelvin Helmholtz clouds”, a beautiful but very rare cloud type, for an example click here. Helmholtz realised that the formation of these clouds required that two layers of air rubbed against each other. In the region between the two layers, the air became unstable, wavy and finally showed the whirls which are actually a series of vortices. As these vortices developed, the two layers of air would get more thoroughly mixed and it was in this way that friction could develop in the upper atmosphere.

Such vortices and “surfaces of discontinuity” are now an important concept in many places including the coffee cup. The video “Coffee Rings” presents another manifestation of the effects of surfaces of discontinuity. So we have returned from contemplation of the wind in a late summer square in London, through a famous Coffee House and back to the coffee.

I have not yet had the opportunity for myself to see a Kelvin Helmholtz cloud. If any reader has been so fortunate please share photos with @thinking_bean. Let me know what you think and what you see around you in the comments section below and most importantly, enjoy your coffee!

*from E. Halley, An Historical Account of the Trade Winds, Transactions of the Royal Society, 1686, p. 133, via “From Watt to Clausius”, DSL Cardwell, Cornell University Press, 1971

†Quotes taken from Anders O Persson, “Hadley’s Principle: Understanding and Misunderstanding the Trade Winds”, History of Meteorology, 3, (2006) p. 17 (linked in article)