Flames stand up for Hallelujah (Part 2)

In Part 1, of Flames stand up for Hallelujah, I explained standing waves and used the immensely popular fire-breathing Ruben’s tubes to illustrate them.

We can now begin to explore particular lyrics of Hallelujah, the song by Leonard Cohen, that mentions “the fourth, the fifth, the minor fall and the major lift”.

To recap, standing wave patterns form from perfectly timed interference of two waves in a medium – passing along a string fixed at one end, for example. Take a quick look at the previous post if you need to refresh your memory.

So, while the waves travel in opposite directions they still have the same frequency. The frequency that produces a single standing wave on a given string is called its resonant frequency. That will change according to what it’s made from and its length, tension and thickness, among other things.

The lowest frequency that produces a standing wave is the fundamental. It’s also called the 1st harmonic. It looks like this:


Fundamental or first harmonic

Fundamental or first harmonic


The arrows show the oscillating movement of the string.

Any frequencies higher than the 1st harmonic are called overtones and they only occur at particular frequencies. The frequency that produces two standing waves, in the same length of string, is called the 2nd Harmonic (1st overtone). Three standing waves becomes the 3rd harmonic (2nd overtone) and so on. So each harmonic is a simple multiple of the fundamental.



Harmonics are the nodes of a vibrating string. After W axell 

This is called a harmonic series. There are many different series because the fundamental can be any note. What is important is the relationship between the harmonics and that doesn’t change.

When it comes to musical notes, the distance between the 1st harmonic and the 2nd, is an octave. No matter which note frequency you start with the 2nd harmonic will always be twice its frequency. If one note, for example concert A, has a frequency of 440 Hertz (Hz) then A one octave above will be twice that at 880Hz and the one below will be 220Hz (half). In fact, any note vibrating at twice the frequency will be an octave higher so the 6th harmonic will be an octave higher than the 3rd. The eighth will be an octave higher than the fourth.

We can see that the ratio is 2:1 – the higher tone makes two vibrations in the time that the lower one makes one. Similarly, between the 2nd and 3rd the ratio is 3:2. That is, the higher tone makes three vibrations in the time it takes the lower one to make two. However, when a string is plucked the tone we hear is the sum of all its harmonics blended together. It’s what gives an instrument its particular sound.

The relationship between these frequencies is what determines whether notes played together sound good or not. If they sound good they are consonant; if they don’t they sound totally out of tune and dissonant. The lower the ratio, the more often the waves coincide and the sweeter the sound it has. The more dissonant frequencies have high ratios.

Chords are several notes played at once. Three notes played together form a triad which forms the basis of many popular songs. It is important to get the right combination of notes, though, or we end up cringing!

Musician playing guitar

Pitches that are too close together sound “off” so a chromatic scale of twelve is used to make the steps all the same distance apart in an octave.

A musical scale is a set of notes ordered by fundamental frequency. Each scale is made up from a select bunch of 7 tones from the twelve no more than 2 and a half steps apart.

Two common scales are major (happy sounding) and minor (sad sounding). The key, is the starting note for the scale. Most people are familiar with the DO RE ME FA SO LA TI DO degrees of the scale – 7 tones plus the return tone to bring us home and not leave us hanging. Try singing it without the last DO and you’ll see what I mean! These 8 notes form the diatonic scale.

The C major scale has the notes C D E F G A B as shown on this keyboard:


Each chord is built from a combination of particular notes and there are 7 diatonic chords in the C major scale. Each has a function relative to the key note and they are designated with Roman numerals. Have a look at the “F”. It is the fourth note of the C major scale. The F chord built on this 4th note of the scale is called subdominant or IV. The G chord built on the 5th note is called dominant or V. So a chord progression from F to G is “the fourth, the fifth”.  In this case the VI is the relative minor the so-called minor fall and the major lift is the progression from G to A minor (VI) back to F. Hallelujah!

It has been fun exploring standing waves and Ruben’s tubes to figure out the lyrics to the song. And it’s good to know no matter how many times I listen to it I still get goose bumps.














Flames stand up for Hallelujah (Part 1)

The song that inspired this post is the popular Hallelujah written by Leonard Cohen and sung here by Jeff Buckley.

Artwork © by Lauren Delora Sears.

One of the great things about staying in post-graduate residential accommodation, here in Dunedin, is undoubtedly meeting some great people from all around the world. I met a lovely Dutch professor here – Maria. We chatted, on and off, as our busy schedules allowed and met up for drinks a few times. On one of those occasions, in fact the last one, we drank a glass or two of wine and played each other some of our favourite music. We both love classical music, and other genres, but at one point she showed me a clip of an Irish priest – Ray Kelly – surprising a couple, at their wedding ceremony, by singing Hallelujah. He did a fantastic job and was happy that I watched because it went viral and several versions have been taken down. Apparently Sony, who own the rights to the original song, is now looking to make a recording with Father Kelly.

It reminded me that Hallelujah is one of those songs which gives me goosebumps. Most people have their favourite rendition of this song. Jeff Buckley’s, seems to be the all-time favourite, with almost 43 million views on YouTube. Although Father Kelly’s managed his 34 million hits in just a few days.

Then there is an amazing version by an eight year old gospel singer! A couple of versions by young women have recently appeared which are worth listening to – Jodi, Alana, Morgan and Hannah Trigwell.

However, the version I usually play is by the talented Michael Henry and Justin Robinett. Interestingly, it’s the two versions with harmonising voices which draws out my goosebumps, as good as the others are. These guys are seriously talented and they have a great sense of humour as their YouTube videos show. But it’s their stunning display, playing Michael Jackson’s Billie Jean, that blows me away. The play simultaneously on twin drum sets and two keyboards while passing the drumsticks back and forth between them. It’s not one of my favourite songs but I love this!

Back to Hallelujah, though.

The lyrics in the first verse got me wondering. It goes:

I’ve heard there was a secret chord

That David played and it pleased the Lord

But you don’t really care for music do you?

It goes like this the fourth, the fifth

The minor fall and the major lift

The baffled king composing Hallelujah.

 But what exactly is the fourth, the fifth, or a minor fall and a major lift?

In order to find the answer to that, we first need a small detour, to explore what standing waves are.

Back in my very first post I explained how sound is energy that moves air molecules. Air is first compressed then extended (rarefaction) and is heard as sound in our ears. The sound is actually the minute variations in air pressure caused by the movement of the molecules. As they bunch up, during compression, the pressure increases and as they spread out again, during extension, the pressure drops. So the sound pressure created by a sound wave may be higher or lower than the surrounding air.

This principle is spectacularly demonstrated with the popular physics experiment using a Ruben’s tube. A Ruben’s tube is a long metal tube, sealed at both ends, with evenly spaced holes along its length. One of the seals is attached to a frequency generator or speaker and the other to a propane gas source which pumps the tube full of gas. The gas is lit as it escapes from the holes.

Particular frequencies for that tube will create standing waves and this is where the beauty of the tube comes in. When the frequencies are just right the flames emanating from the holes will show the pattern of the standing wave. There have been numerous posts lately on the topic since a video of a pyro board was put on YouTube.

So what is a standing wave?

Waves can be generated in the air, for example a woodwind instrument, or along a string such as a guitar string. It’s best explained by the idea of a string which is fixed at one end. Try it by fixing a piece of rope to a tree.

If a single pulse (wave) is sent along the string it will be reflected back along the string, once it bounces off the tree, except it will be upside-down. If another pulse is sent, soon after, the wave travelling in the opposite direction meets the first and they interfere with each other. This interference can be destructive or constructive. If several pulses are made, the result on the string usually looks pretty chaotic as they either add to, or subtract from, the others at different points.

However, if they are well timed, a standing wave can be created. Here, the advancing wave and the reflected wave meet and the whole string oscillates up and down.

Standing waves caused by interference between advancing wave and reflected wave.

Standing waves caused by interference between advancing wave and reflected wave.

The nodes are the places where there is no displacement and the antinodes are where there is maximum displacement. Each frequency has its own pattern.

Now back to the Ruben’s tube.

The height of the flames is proportional to the gas flow which depends on the pressure inside the tube relative to the outside. Since the tube is sealed, the gas has only one way to escape – out through the holes! The pressure it is under at the point where the gas passes under the hole determines how high it will go.

The pressure inside the tube before applying the sound is the same so the flames will all be the same height. When the sound is applied, at one end, the compressed waves produce high flames and the rarefaction produces low flames. The lowest flames correspond to the nodes and the highest flames to the antinodes.

Ruben's Tube standing wave pattern showing flame height relationship to pressure.

Ruben’s Tube standing wave pattern showing flame height relationship to pressure. Credit: Tools for Teaching Science

So now that we have the standing waves sorted, I can look at what this all means for those Hallelujah lyrics in Part 2.

Flood – When a five hour journey turns into twelve

Song for this week is Tool’s Flood.

from dreamxspace

This week, for the second time in two weeks, I had to make the trip between Christchurch and Dunedin during a severe weather warning.

At the start of Easter, my classmate and I left Dunedin and headed for Christchurch. It was the start of a ten day break and we were both looking forward to going home to be with our partners. I was staying in Christchurch but she was flying out in the very early hours next morning bound for Sydney.

I picked her up just after lunch and we began the five hour journey by car. There was a severe storm approaching, and we had been warned to take it easy, but I have driven that road many times before and it didn’t really faze me. Rain had been plummeting from the sky for several days, on and off, and the ground was pretty well saturated. Tiny creeks, at the side of the road that were usually barely noticeable, frothed in a cappuccino cascade. The waves crashing in on the stretch of beach at Katiki were wind-whipped and wild so we stopped, very briefly, to try to take some pictures. Not a chance! Gusting gales and horizontal sprays of rain and sand on my lens, forced a hasty exit. The rain had plenty of time since it wasn’t due to get dark until 7pm. We’d be well home by then since I was happy to drive slowly and carefully and have several stops. Or so I thought.

Approaching Hampden, a small settlement between Palmerston and Oamaru, we noticed a line of traffic ahead of us. It looked like an accident or something further along the road so we waited patiently in the queue. We watched the traffic continue to come towards us from the other direction for about fifteen minutes. That seemed odd. I switched off the engine and we waited while the traffic behind us backed up. Still, the opposing traffic seemed to flow freely. After another ten minutes, we saw a bedraggled man wandering down the full line of stationary traffic towards us. One by one, the windows of the cars in front of us rolled down and he leaned in for a few seconds to speak to the travellers inside. Then it was our turn.

“Bridge is closed at Maheno”, he said. Then he added, “Can’t go back to Dunedin either”.

The Kakanui River had flooded, yet again.

Records of flooding on the Kakanui go back to 1868 and, back then, damage extended over a wide area and people lost their lives. Its catchment area is almost 900 square kilometres. One quarter of that is in upland mountain areas with steep sided slopes and the river runs in a single thread or is slightly meandering. The steep ground means that more water runs straight off over the surface (runoff) rather than soaking in (infiltration).

Drainage Basin System credit: Andrew Bennett

Drainage Basin System credit: Andrew Bennett

Low rolling hills and valleys make up the remainder. They have gentle gradients and the river channel migrates and braids. On gentler slopes there is more infiltration than runoff – unless the ground is already saturated and can’t take any more. Rainfall is measured in mm and the highest recorded during a storm is peak rainfall. Flooding is the catchment’s natural response to a deluge of rain.

Hydrologists are interested in the characteristics of the river when it floods. The discharge is the amount of water flowing through the river at a given time and it is measured in cubic metres per second (cumecs). The highest discharge resulting from a storm event includes the water, sediment and other matter in the river. This is called peak discharge. Plotting this information on a hydrograph gives a sense of what is happening over time. The rising limb is the time that the river is experiencing increasing discharge. The receding limb shows the reducing discharge and return to normal flow.

Storm Hydrograph credit: Andrew Bennett

Storm Hydrograph credit: Andrew Bennett

The time from the first rain drops to the time there is a change in the discharge is called the river’s response time. If rain keeps falling discharge keeps increasing and bankfull discharge is the maximum amount of discharge that a river can hold before bursting its banks.

The problem we faced was that there was a lag time between the rain falling in the catchment and the time of peak discharge. The rain had been falling there for a while before we left Dunedin.  It takes a while for the high flows to propagate downstream from the upper reaches. So flood alarms are tiggered when the rainfall at Clifton Falls in the Upper Kakanui reaches 40mm in 24 hours and there are several stages flood warnings depending on flow. Civil Defence is notified when it is flowing at 267 cumecs at Clifton Falls as this will be much greater downstream where State Highway 1 crosses it at Maheno. The road is closed once it reaches 420 cumecs here.

Kakanui rainfall clifton falls to 1 mayKakanui flow CF to 1 may

The Otago Regional Council graphs show the rainfall and flow at Clifton Falls Bridge and the summary of flow for that week showed a minimum flow of 6.3 cumecs and a maximum of almost 580 cumecs. No wonder we couldn’t get through! It would take a while for the river to recede.

Apparently, the traffic that had been driving past us had been either local residents or fed-up folk who had pulled out of the line. Every now and then the cars would creep forward to take up the vacant space.

Hampden, on Easter Friday, is not the best place to be trapped by rising floodwaters. The phone signal was intermittent but I managed to check traffic updates. It looked there would be an update within a couple of hours. Luckily, we were able to pull out of the queue once the car reached a small side road. We got out and went off to explore Hampden’s culinary delights and returned to watch a couple of sitcom episodes on our laptops.

Time was marching on so Elsie ventured out in the wet to check out the situation. We were told the road was closed until midnight. Waiting in the car for that amount of time was highly unappealing and it meant we’d get in to Christchurch just before 4am.

No question –  we had to have a plan B.

“Are you up for an adventure?”, I asked.

“Sure”, was the reply.

I phoned my partner to find out the state of the Pigroot – the route from Palmerston through to Central Otago – an enormous detour but doable. He said there was some flooding but that it was still open. If the road opened at midnight we’d still have 8 hours of sitting around in the car and, personally, I’d rather be driving. It would take us at least 8 hours from here so we bolted for Palmerston.

We travelled inland through to Alexandra, past the Clyde Dam to Cromwell and up through the MacKenzie Country to Tekapo. Once we got near Alexandra, the rain eased and from there the rainfall was sporadic. By the time we got to Tekapo the skies cleared and we saw the new moon shining brightly. We made a small detour to stop at the Lake Tekapo for a few minutes to watch the moonlight reflect on the water and highlight the top of the hills behind the township.

Back on the road, it wasn’t long before the murk again filtered through Burke’s Pass. From here, the journey home was wet and miserable as we veered away from the shelter of the hills and ever closer to the East Coast.

Bleary-eyed, I pulled into the driveway just after 1am. We heard later that they had reopened the road at 8.30pm and we may have made it home a little earlier but I was pleased to have been doing something active rather than sitting and waiting.

While it is an inconvenience to be held up because of flooding it is important to take care. Thank goodness no-one has been lost recently although a woman was rescued from her car after being swept down the river as we were heading north!

I guess more flooding is something we’ll have to get used to, given the prediction of increased storminess, due to climate change. Understanding more about rivers and flood dynamics can help with travel planning at the very least. We’ll know for next time.

Checking out the long legs of liquid gold

Artwork © Lauren Delora Sears

Today’s song couldn’t really be anything other than Whiskey in the Jar by The Dubliners but it highlights the different spellings of whiskey (in the song) and whisky (in this post). The Irish spell it with an ‘e’ to differentiate it from Scotch whisky which is produced in Scotland under a myriad of rules and regulations. Needless to say, I felt compelled to stay true to my Scottish roots by referring to whisky.

And it seems that, if you’re Scottish, you are highly likely to have whisky flowing through your veins. In fact, it appears so common to love the tipple that I sometimes feel I’m the only exception!

The alluring, and seductive, liquid gold takes pride of place at tables in pubs and living rooms across the country – and the world. Sensory exploration of its nuances in character can keep whisky buffs entertained until the wee hours. I have seen that first hand. Like most things, people have personal preferences and whiskies are usually classified according to geography and flavour characteristics. Yet, even though I don’t like it at all, I have come to be able to recognise basic divisions according to how it looks and its aroma.

In actual fact, we use our senses of sight, smell, touch and taste, to evaluate whisky. And usually in that order.

Whisky is essentially a mix of flavoured water and alcohol. One of the first things a whisky drinker does, after checking the colour, is to swirl it in the glass and observe the formation of whisky ‘tears’ or ‘legs’.

Whisky legs. Photo credit: tienvijftien

Whisky legs. Photo credit: tienvijftien

Legs are drips, that flow downwards from a ring of clear liquid on the inside of the glass, above the surface of the whisky. They’re also known to form in wine. The length of the legs gives an indication of  alcohol content and they are created by the difference in surface tension between the two liquids.

Surface tension is caused by the tendency for molecules at the surface of a liquid to stick together (cohere) strongly. These cohesive forces are shared between all the molecules but, because there are no molecules above them, the ones at the surface bond with those alongside even more strongly. This is especially true for water molecules.

The increased bonding forms a line of resistance just like a row of people with linked arms. Just as you would huddle tighter in that row to prevent anyone breaking through, the surface of the water contracts. That is what is responsible for the spherical shape of water droplets. That extra resistance on the surface is also what allows water striders to walk on water without breaking through and sinking.

So, as the whisky in the glass is swirled, a thin film of the mixture is pushed up the side of the glass. Water and alcohol are both evaporated from the surface of the glass but alcohol is evaporated faster. This reduces the alcohol concentration of the film and a greater proportion of water is left on the glass.

Since water has a higher surface tension than the alcohol, and the bulk of the mixture, more whisky is hauled up the side of the glass, creating an upwards flow. The water at the top of the film beads, at first, then starts to flow downwards back into the whisky as gravity takes over. The higher the alcohol content of the whisky, the more easily and further the water can pull the mixture – hence longer legs. This phenomenon is called the Gibbs-Marangoni effect after Italian physicist Carlo Marangoni and American physicist Josiah Willard Gibbs who both worked it in the middle to late 19th century.

The alcohol content also affects the texture or feel in the mouth. If it is high, it can dry the mouth and be considered fresh. Whisky with lower alcohol content covers the mouth with a smooth, viscous coating. Although I must admit, I think I’ll leave that bit to someone else!

Move and be moved – the power of music

Artwork © Lauren Delora Sears

Do you ever just start moving to a piece of music and you feel like you can’t help yourself? It can be embarrassing in public but nowadays I don’t care. Unfortunately, for the past few weeks I have been too busy to listen to music. I know. I know.  That seems so crazy but it’s true. For me it is unheard of – I love music and if it has a beat, well, something starts to move.

Our bodies respond to all kinds of external stimuli. With music, we usually respond to rhythm first. Sometimes, I find myself toe tapping to music I don’t even like. And I feel compelled to sway, jiggle, or sashay across the floor – at least when I’m alone – when invigorating music comes on. It would take something totally abhorrent to my personal sense of aesthetic to stop me from doing so.

Back in my school days there was a sound that, even now, creates a more noticeable and lasting response. Fingernails on a blackboard! It doesn’t seem quite the same with a whiteboard. The sensation is so vivid I can just hear the words ‘fingernails on a blackboard’ or imagine it happening and it evokes that spinal chill. I have already had 3 or 4 just writing that sentence!

Even better is the intensely pleasurable experience we get from particular sounds. The neurons in our brains get quite excited by specific characteristics of sound and produces the amazing sensation of goosebumps or aesthetic chills when we hear music that we adore. There are certain pieces of music that many people respond to – Puccini’s Requiem is one. Others are more specific to individuals and some don’t get it at all. The goosebumps are definitely a very pleasurable experience and it lets you know that the music has hit that sweet spot. The music activates the pleasure and reward structures deep within the brain which are also active in response to other natural and pleasurable stimuli such as food or sex.



Photo credit: Ildar Sagdejev


Certain musical events within a song can trigger the reaction and for me it usually involves harmony and or powerful voices.  But not just any powerful voices. There is clearly something very particular, yet indefinable, that sets it off. Sometimes it is unexpected. At other times I know exactly which singer, piece of music, and part in the piece that will do it. It enhances the whole feeling. I used to try to fool myself. I’d think of something else, hoping to avoid it, but some pieces are so strongly resonant they slip through the defences. Before I know it, the hairs on the back of the neck are standing to attention so I no longer try. One of my earliest memories of a song that elicited the goosebumps was the harmony in Eagles’ Seven Bridges Road.

The technical name for goosebumps is piloerection. It occurs in many animals including porcupines and, of course, frightened cats. When threatened their hair, fur or spines stands on end to make them appear bigger.

How does the skin get those bumps?


Goosebumps (piloerection)

Goosebumps (piloerection)

The hair follicles have tiny muscles attached to them called Arrector pili muscles. When they contract they pull the surrounding skin downwards creating a depression leaving the follicles high and dry – the bumps!

The hairs stand erect stretching upwards into the air and increasing sensitivity to small stimuli. With threats, you’re on high alert and hypersensitive. With music, it maximises the sensation and it is just glorious!

Psycho-physiologists can test our physiological response to music and match it to the subjective feeling of the listener. The pairing of the physiological response with subjective feeling is very useful for emotion research. The most common measures of such emotional arousal are the Skin Conductance Response (SCR) and the Heart Rate (HR).

The level of arousal we experience can be directly measured with SCR.  Like the cat and porcupine, our bodies are geared to respond to threat using the ‘fight or flight’ response. Either of those requires some serious activity! The human body prepares by sweating more to cool itself down. It happens all the time, as we respond to emotions or thought, but it occurs at such low levels we barely notice it. When the threat becomes large enough those sweat glands go into overdrive. We all know the sweaty palm feeling when we’re particularly anxious about something, like exams, job interviews or stage performances. By placing electrodes on a finger, and placing a small painless current across them, scientists can measure the increased skin conductance from the perspiration.

Music has the ability to affect our emotional states and transport us to a different time or place. It can rev us up to provide motivation via those reward centres when there is something particularly mundane to deal with ahead of us – think housework music! We can also calm ourselves down and change our arousal levels, a fact long known by mothers who have sung a lullaby to a baby at bedtime.

Music is one of life’s pleasures that is intensely personal and emotional so it must be strange to never experience its thrills and chills. Scientists are now beginning to relate these responses and experiences to aspects of personality and even our genetic code. I can’t wait to see what they discover.

Seeing Mountains through a Microscope

Today’s song is from the harmonious Civil WarsOh Henry. Artwork above © Lauren Delora Sears.

As I get older, I appreciate the white space more and more. Designers know that the white space is as important as the rest. It provides context, balance and a container in which to arrange the content so we can easily find and navigate through the important stuff. The white space in our lives gives us room to step back and reflect. And it is this process of reflection that consolidates our learning and sparks creativity.

The hustle and bustle of life in the modern world barely offers a nanosecond of time for reflection. We rush from one thing to the next, be it job, project, relationship or adventure – always focussed on efficiency, productivity, utility and economy. It is hard to imagine a world where you had the means to pursue a career entirely of your own choosing, and construction, with little regard for the mundane necessities of ‘real world’ existence that plagues us all. The freedom to follow your heart or intellectual curiosity is a precious gift which is rarely afforded to us.

For academic researchers, the importance of this freedom and time for reflection is embodied in sabbatical leave. The notion that it was a frivolous exercise and a complete waste of time has been raised several times throughout history. But it is often when reaffirmation and rejuvenation take place. The loss of such a crucial part of the research process would be lamentable. Increasingly, research is expected to become more applied. With limited funding available for science research there is an expectation of a payoff. And sooner rather than later. So something has to give with the burden of administration, teaching and research all competing for time. Dr Tamson Pietsch notes that many researchers now do research in their leisure time.

The demands placed on the scientific research process by the modern obsession with utility and economic evaluation could have a profound effect on our ability to adapt to a rapidly changing environment.  This myopic vision reduces research diversity and alters the process and direction of intellectual endeavour.

I see this appropriation of scientific potential and subsequent loss of diversity as akin to a population bottleneck. There are many instances where the value of particular research has not been realised until much later. It takes time to acquire knowledge, build upon it, reflect upon it and stimulate creativity. As Dr Pietsch points out, fishing for ideas is like fishing for trout – it takes time. You can’t force creativity no matter who is doing the table thumping. So in the event of a concentration of research in favoured areas the ability to switch focus, and resources, will be compromised.

Fortunately for us, there have been individuals throughout history, who have had the time for research and reflection without some of these constraints. Their contribution to science today is immense largely because they were not hamstrung by bureaucratic, political or financial impositions. They were known as gentlemen (they were usually men) of independent means. Included among them was the famous Charles Darwin (evolution).

But another, hardly known outside of geological circles was Henry Clifton Sorby.

In the year that Queen Victoria became monarch of the United Kingdom he was only 11 years old. By the time he had turned 15 he was already determined to pursue a life in science.

In a bittersweet turn of events, Henry’s father died, leaving Henry a sizeable sum. It was enough, in fact, for him to become one of those gentlemen of independent means at only 21 years old. It is hard to imagine your average 21 year old, these days, choosing to pursue a life of science, in their leisure time, when such a windfall comes their way! But that is precisely what he did.

Marine science, geology and metallurgy fascinated Henry. He sailed around the North Sea coast indulging his interests in marine biology and geology. He’d collect small marine organisms which he then meticulously prepared and mounted on glass slides. Henry soon realised that the microscope could also be used to view rock samples in a very different way.

First, he pioneered the techniques for examining rock in thin section. It is now the standard method by which geologists come to understand the origins of rocks. For Henry, it would have been a laborious task, hand grinding the rock down to slices “1000th of an inch” thick. This allowed light to be transmitted through the previously opaque rock, revealing detailed structure and micro-textures.


Thin section showing aligned minerals in the structure of the rock © GNS Science.

Poor old Henry was initially laughed at for attempting to view ‘mountains’ under a microscope. However he persevered and thank goodness he did! He went on to find microscopic fluid inclusions within the mineral grains. These tiny bubbles of liquid or gas are trapped within the mineral, at the time of its formation. They provide clues to the temperature and pressure conditions which existed at that time. His pioneering work with the microscope laid the foundation for modern petrography – analysis of those detailed structures and textures.

A modern petrographic microscope, used to look at thin sections, is different from the standard microscope that biologists use. The petrographic microscope has the addition of two polarising filters, oriented at right angles to each other, and a rotating stage which the sample sits on.

Cross polarised light © Olympus Microscopy

Cross polarized light © Olympus Microscopy


Light, travelling up from the its source at bottom of the microscope, passes through the first polarising filter before reaching the sample. Only light vibrating in a direction aligned with the polariser is allowed through. This is called plane polarised light.

Thin section under plane polarised light © GNS Science

Thin section under plane polarized light © GNS Science


A second polarising filter is located above the sample and this can be turned on or off. When it is turned on the plane polarised light is blocked (crossed polarised light).

Thin section under cross polarised light © GNS Science

Thin section under cross polarised light © GNS Science

Olympus Microscopy have a good interactive tutorial that allows you to play around with changing the angles of the polarising filters.

Rotating the stage makes some minerals appear black briefly when the polarisation prevents the light from getting through. Some minerals produce beautiful, vivid colours caused by interference during refraction of the light rays through the mineral. By careful examination of each mineral’s different optical properties geologists can begin to reveal the composition and origin of the rocks.

Vivid colours produced by interference © GNS Science

Vivid colours produced by interference © GNS Science

Present day geologists owe a great deal to the efforts of Henry Clifton Sorby and others who were lucky enough to have time to think and pursue their interests at their leisure. And we all can appreciate the artistry and histories revealed by Henry’s unwavering commitment and passion for his science.

Romancing the stones – finding beauty in the bedrock


I see you

The veil of objectivity

we drape you in

belies your tortured past


I hear you

Tumbling vociferously

thundering endlessly

pulverized to dust


I feel you

Jaggedly striking

an angular figure

and textured frame


I see you

Embracing ancient

lifeless forms which

mark your passing years


I hear you

Thrum and pulse

scrunch and crackle

as blazing spasms flow


I feel you

Cool, smooth satin

glides across my cheek

like curling stones on ice


I see you

Bright and bejewelled

glinting beacons ushering

us across the abyss


I hear you

Groan, creak and screech

the belly-aching refrain

from a twisted visage


I feel you

Crumpled and gritty

stoic astride

your innermost flux


I see you

Pretty pictures

painted in scorched film

adorn your face


I hear you

Harmonic vibration

a mellow hum

murmurs through time


I feel you

Strained and supportive

an edifice

beneath my feet