19 June 2012

Leonardo da Vinci - Anatomist

Leonardo da Vinci (1452-1519) is undoubtedly remembered foremost as a gifted and talented artist, yet nowadays he is perhaps becoming increasingly well known as the archetypal ‘Renaissance Man,’ whose interests and exploits were not simply confined to our more specialised notions of what defines an artist. Certainly, a proliferation of books and exhibitions over recent years has increasingly focussed on redefining him as Leonardo, the scientist.

Leonardo was indeed a polymath, equally as interested in art as he was in tackling problems of engineering, optics, geology, hydrodynamics, biology, philosophy, architecture, medicine, arithmetic – the list goes on. Indeed, Leonardo saw all these subjects as essentially one and the same. They were all interconnected. It seems only logical that an artist wishing to create enormous sculptures should concern himself with fundamental principles of engineering; likewise, an artist who is seeking to accurately portray the human body in action with convincing emotional expressions would do well to study basic human anatomy. In the last hundred years or so, scholars have been looking at Leonardo’s notebooks and finding in them a window into his remarkable mind.

Sifting through his extant manuscript sheets and the pages of his surviving notebooks (only a bare fraction of what he is thought to have created during his life) we encounter Leonardo first-hand. The writer, Charles Nicholl has written a wonderfully evocative and well-informed biography, titled Leonardo da Vinci: The Flights of the Mind (Allen Lane, 2004). And, in an equally engaging and fond essay on the notebooks, Nicholl sums up Leonardo’s style of writing: “[H]e is not a writer in a literary sense. Rather, he is a writer-down of things: a recorder of observations, a pursuer of data, an explorer of thoughts, an inscriber of lists and memoranda … In painting he is a master of nuance, but as a penman he tends to the workmanlike. At its best his writing has a marvellous uncluttered clarity … There are many beautiful sentences in the notebooks … The words are pared back to the quick; it is a statement of lucid simplicity into which complex scientific questions are folded.” – see: Charles Nicholl, Traces Remain: Essays and Explorations (Allen Lane, 2011).

But for Leonardo the words were far less important than the sketches to which they were appended. For instance, next to one of his anatomical studies of a heart we find the accompanying passage: “O writer, what words of yours could describe this whole organism as perfectly as this drawing does? Because you have no true knowledge of it you write confusedly, and convey little understanding of the true form of things … How could you describe this heart in words without filling a whole book? And the more minutely you try to write of it the more you confuse the mind of the listener.” These words could well have been intended as an admonishment to their author just as much as any other unnamed writer, especially when we see Leonardo getting lost in his own ever more minute descriptions of the workings of the heart at the end of his long years of in-depth anatomical study (given up, poised on the cusp of ‘demonstrating’ the correct system of circulation). These words serve to remind us that Leonardo was for the most part not writing for us; primarily he was writing for himself, whilst aiming towards a final publication that never came to be. As with all such notebooks belonging to artists and scientists alike – they were working notebooks: repositories for ever evolving thoughts and ideas, where facts were weighed and sifted, processes experimented with and refined – they were active works in progress; their contents remain frozen in time, rare survivals for us to review and speculate over with fascination.

My own fascination with Leonardo da Vinci began when I was around the age of 11 or 12 years old. I was taken to see an exhibition of Leonardo’s drawings held at the Hayward Gallery on London’s Southbank. I vividly recall staring at Leonardo’s plans for an amoured tank, looking like a wooden ‘B-Movie style’ flying-saucer, bristling with cannon. There was also a life-size model of his famous flying machine, a huge wooden contraption which he intended would give a person wings, like those of an angel; yet its design remained impractically doomed, like the mythical Icarus himself. This exhibition had certainly fired my imagination, and spurred on by school science lessons, in which we dissected sheep hearts and pig’s lungs (I remember my teacher daring me to be the first to poke my little finger down the open aorta, which I intrepidly did much to the shocked-mirth of my classmates!); so much so that I bought myself a hard-backed notebook, like Leonardo’s, and, using my mother’s old book of Basic Anatomy and Physiology by C.F.V. Smout (Edward Arnold, 1967) originally bought for her nursing studies as my primer, I set about creating my own meticulously detailed medical drawings.

Originally I was intrigued by the workings of the human body, but the blood and guts side of it all began to get the better of me and I found myself honing in on one particular area, namely the structure of bones and the mechanics of how they worked. As I progressed through school my squeamish side eventually won out altogether and other subjects eventually superseded and took precedence. But, unwittingly my budding Leonardo phase was to stand me in good stead, as many years later I found a basic understanding of skeletal structures came in handy when working on archaeological excavations. Although I’ve never actually excavated a human skeleton myself (I did once excavate a headless dog’s skeleton!), I have worked with human remains in museums. Some ten years ago now, my mother’s copy of Smout’s Basic Anatomy and Physiology (which I still have) was utilised once again when I was charged with recreating an accurate display of the burial of a Bronze Age archer. In the course of which I discovered he had several fused vertebra in his neck and lower back. It was a fascinating task and taught me that my love of all things Leonardo-like had never really died!

Consequently, it was with great interest that I’d read earlier in the year of the current exhibition being held at the Queen’s Gallery, near Buckingham Palace – titled: Leonardo da Vinci: Anatomist (May 4th – October 7th 2012), which I spent several engrossing hours visiting today. This is an unprecedented exhibition of 87 of Leonardo’s finest anatomical studies. The exhibition charts Da Vinci’s two most sustained periods of anatomical research, spanning several decades of his life, evolving out of and continued alongside his dissection of both animal and human corpses.

Leonardo begins from the basis of received knowledge, theories as to the workings of the body and the essential emanation of life, handed down from classical authors; but through the process of genuine scientific study he starts to move away from supposition and begins to root his knowledge in grounded facts – trusting what he sees and what he can prove (through experiment and simulation) over what he originally believes. For instance, in an early drawing dated around 1490-1492, he depicts two channels in the penis, which he believes are necessary for the transmission of the vital elements (animal, spiritual, and material) during reproduction, which he subsequently draws correctly as a single channel in a later and more detailed study of around 1508. Likewise, he also refines certain concepts, adapting them to the reality of what he finds in the course of his dissections. Again in 1490-1492 he draws a cross-section of the human head in which he shows three bulbous ‘ventricles’ in the brain, each neatly lined up one after another; yet by 1508-1509 he has conducted an experiment using a truly innovative method of dissecting the brain (having first injected it with molten wax to better preserve the shape of such internal cavities) and thereby finding a much more complex form of arrangement for these cavities.

However, not even Leonardo’s meticulous rigour could wholly avoid some degree of conjecture. Whilst we know he was able to dissect a number of human bodies he was also compelled at times to supplement gaps in his investigations by making extrapolations from animal corpses which could differ subtly from the same organs as found in humans. In his famous diagram of a child in utero (which it seems likely from other details he did actually see directly for himself), he has added specific features to the make-up of the wall of the womb which are found in cows rather than humans.

Leonardo’s anatomical investigations come to an end with detailed investigations into the working system of the heart. Based on the dissection of ox hearts he accurately draws the chambers of the heart and its valves, and he is the first not simply to note the existence of what has since been named as the sinus of Valsalva, but also the first to demonstrate what its actual function is. He did this by making an accurate glass model of the aortic valve, through which he pumped water containing grass seeds, and this showed him the vortices in the flow. He concluded that these vortices were instrumental in closing the valve – a finding which wasn’t confirmed until 1912, exactly four hundred years later.

These drawings show but one facet of Leonardo’s brilliant and seemingly fathomless mind. And we are left at the close of the exhibition pondering what might have been had Leonardo been able to pursue his investigations to the end of his aims and publish a treatise which would certainly have significantly advanced the progress of medical science at the time. Instead, they languished largely unknown and certainly unappreciated for centuries. Like the scholars of Hellenistic Alexandria who invented the basic apparatus of a steam engine but never managed to take that next step and channel its actual power, history it seems is full of ‘nearlies’ and ‘what might have beens.’ Who knows, perhaps if I’d studied harder at my Da Vinci and my Smout drawings I might have become a high-flying heart surgeon … or a half decent high street butcher!

This is a truly excellent exhibition, well worth a few hours of your time. For more information see the following article: Leonardo’s AnatomyYears (Nature, Vol. 484, 19 April 2012) by Martin Clayton, Senior Curator of Prints and Drawings at The Royal Library, Windsor Castle, and curator of this exhibition.

Many of Leonardo da Vinci's anatomical studies can be seen in more detail on-line at the Royal Collection's website. For more information about visiting the exhibition click on the image below.

6 June 2012

The Transit of Venus

June 5th & 6th 2012 mark the last dates this century when the Earth, Venus, and the Sun will be in perfect alignment. The next chance to view this celestial phenomenon will not arise until the year 2117. And sadly, at the time of writing, the weather forecast for the UK doesn’t look particularly favourable.

When the Sun rises today at 4:45 am in London (4:30 am in Edinburgh, 5:15 am in Penzance) the transit will already be in progress. If the clouds don’t spoil the show and we are able to observe the sun, with the right apparatus and the correct filters or means of projection (being very careful in order to avoid permanently damaging our eyes), we should be able to see the passage of a tiny black dot passing serenely over the face of the Sun.

The history of observing the transit of Venus is equally as fascinating as understanding its significance in the furthering of our scientific knowledge. Although many ancient cultures were aware of, and so observed and studied the motion of the second planet of our solar system, it seems none of them made any recorded observations of Venus transiting the Sun (at least, none that we currently know of). The famous German scientist, Johannes Kepler (1571-1630) was the first person to attempt to predict the occurrence of the event. In 1621 he calculated that a transit visible from the region of Europe would occur in 1631, but his calculations weren’t accurate enough for anyone to actually observe the phenomenon. Through refining Kepler’s predictions, an Englishman named Jeremiah Horrocks (1618-1641) was able to make a more precise prediction, and he also established that the transits occurred in pairs separated by eight years, recurring approximately every 105 and 121 years.

The importance of accurately observing such transits for the purposes of science were soon noted, and in 1668, the Scottish mathematician, James Gregory (1638-1675), suggested that accurate observations of the transit of Mercury at different points on the Earth’s surface could be used to better establish the distance of an astronomical unit (that is, the distance between the Earth and the Sun). With this knowledge in mind Edmond Halley (1656-1742), the English astronomer whose name is most commonly associated with Halley’s Comet, set out to observe the 1676 transit of Mercury from the island of St Helena in the Atlantic; but he was disappointed to find that only one other observation had been made, and consequently he was not satisfied that this was enough data to make a sufficiently accurate calculation. He proposed that the same system of triangulation could be used in similar observations of Venus transiting the sun, and, although he would not live long enough to make those observations himself, there were others who took up his call.

In 1761, the Royal Society prompted by the French astronomer, Joseph-Nicolas Delisle (1688-1768), along with a number of other learned societies and scholars in different nations despatched expeditions to various parts of the globe – in a truly notable early international collaboration in the shared pursuit for scientific knowledge – to realise Halley’s suggestion. There were more than 250 official observers placed around the globe, many of whom had undergone great hardship and arduous travails against the odds in their attempts to view the transit. We should take solace therefore if our view is clouded out this year, as so were many of theirs; but hopefully we shall only have to suffer the insult of the elements, whereas many of these hapless astronomers-turned-adventurers also suffered the added injuries of being caught in the crossfire of warring soldiers, or suffered attack from hostile peasants, in all kinds of extreme climates!

It was during the transit of 1761, however, that the existence of an atmosphere around Venus was first proposed. A Russian scientist, Mikhail Vasilyevich Lomonsov (1711-1765) noted a curious occurrence as the planet made its first and last contact (ingress / egress) with the solar disc. He saw that an arc of light suddenly curved around the outer edge of the planet, distinctly showing up against the dark background of space; the light of the Sun having been harnessed and conducted by the planet’s atmosphere via a similar principle used in today’s fibre optic technology. On the whole though, the sum of the observations made in 1761 was simply a great disappointment. None of the scholarly calculations made around the globe seemed to agree. Undeterred though the scientific community resolved to try again in eight years time.

And 1769 certainly saw a concerted effort to redress the balance, particularly on the part of the Royal Society, which organised thirty observation points in Britain alone, and more than sixteen overseas. Again it was a truly international collaboration in which many governments, overlooking their own national agendas and despite warring differences, combined in funding a global effort to broaden mankind’s scientific knowledge; a spirit which persists to this day, particularly in the fields of astronomy and space exploration.

Perhaps the most famous of the observing missions of 1769 was that undertaken by Captain James Cook (1728-1779), who was engaged to sail HMS Endeavour to the southern hemisphere in company with the botanists, Joseph Banks (1743-1820) and Dr Daniel Solander (1733-1782). In June of that year Cook set up his observing station on the island of Tahiti in the Pacific Ocean, recording the following entry for the transit in his journal:

“Saturday 3rd. This day prov’d as favourable to our purpose as we could wish, not a Clowd was to be seen the whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk: we very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the Contacts particularly the two internal ones. Dr Solander observed as well as Mr Green and myself, and we differ’d from one another in observing times of the Contacts much more than could be expected. Mr Green’s telescope and mine were of the same Mag[n]ifying power but that of the Dr was greater than ours.”

The difficulty in precision regarding the timing of the contacts Cook describes (as shown in his drawings) is actually due to the so-called ‘black-drop effect’ – an optical phenomenon which you can replicate for yourself if you place your thumb and forefinger close to your eye and then watch as you narrow the gap between them. If you look carefully you’ll notice that the edges of your thumb and forefinger appear to leap together before their surfaces actually meet. In reality this phenomenon didn’t significantly alter the calculations made in 1769, and the scientists of the day were able to determine the necessary trigonometry to establish that the distance between the Earth and the Sun fell somewhere in the region of 92,900,000 miles (149.5 million kilometres) and 96,900,000 miles (155.9 million kilometres) – which isn’t far off from today’s estimate of 92,960,000 miles (149.6 million kilometres).

Despite the fact that nowadays we have many different methods for studying our solar system and measuring its distances, the actual observation of Venus transiting the Sun’s disc is still important scientifically – not least as a marker of the efforts of those early pioneers of science, but also as real science still. Such observations will aid and inform astronomers who are currently engaged in the hunt for planets beyond our solar system, many of which are now being discovered. It will also help them to better determine the sizes of these ‘exo-planets’ more accurately. And observations from Earth will compliment observations made by the Venus Express (VEX) mission, an orbiter sent by the European Space Agency in 2005, which is currently monitoring the Venusian atmosphere. And again such spectrographic studies will assist in determining more about the atmospheres found around exo-planets too.

In the time since Captain Cook observed the transit of Venus in 1769 and the transits of our own era (2004 & 2012), exploration has enabled us to chart not only the Earth but also our solar system and some of the stars beyond. We’ve mastered the powers of flight and managed to send missions the surface of Venus itself, as well as other planets. Watching that small black dot transiting the solar disc or simply shining as the brightest of the planets visible in our morning or evening sky, one can't help but wonder at the immense celestial mechanics which regulate the passage of time and space within our solar system; and then wonder where our explorations will have taken us by the time the next era of people look up to observe the passage of Venus across the Sun in 2117.

For more information about this year’s transit (and that of 2004) take a look at the following page on NASA’s website

And, to coincide with this year’s transit, Random House has published a new history of the astronomer-adventurers who went in search of the transit – Chasing Venus: The Race to Measure the Heavens by Andrea Wulf (2012).