Daniel and his den of diatoms …

After contemplating astronomy-without-optics at Ulug Beg’s observatory (see previous post) we walked ten minutes down the road to another of Samarkand’s sights, the mausoleum of Daniyar (the Old Testament prophet Daniel, also venerated by Muslims).  This was a much plainer structure than the polychromatic wonders we had seen elsewhere in the city and, no doubt as a result, fewer visitors.  Daniel’s sarcophagus runs the entire length of the building: the legend is that his severed leg has continued to grow, necessitating an eighteen metre tomb.  The presence of a group of pilgrims, praying with an Iman, reminded me that our word “holiday” is a concatenation of “holy day”, and that pilgrims were the original tourists, both in this part of the world and in Europe.

Our guidebook mentioned an ancient spring on the site, offering me my first opportunity to mix business and pleasure. Unfortunately, the spring was dry but, following the valley up a steep hillside, we reached a graveyard, beside which there was a water trough whose bottom, when I peered inside, was covered with dark brown circular patches, up to about half a centimetre across.  I had not really come prepared for diatom sampling but managed to commandeer an empty water bottle into which I scraped some of these colonies using a piece of plastic that I found lying on the ground nearby.   The water bottle was then stuffed into my rucksack as we continued our explorations, cutting across country towards another set of monuments that we could see on the horizon (Colin Thurbron describes the same journey in reverse in his excellent book The Lost Heart of Central Asia).   Once we were back at our hotel, I let the sample settle overnight, poured off the supernatant and then added an equal volume of local vodka to the remaining suspension.  As in India last year, this is the quickest and least hazardous way of keeping diatoms in reasonable condition when on the road (see “Diatoms from the Valley of Flowers”).

Left: the water trough near Daniyar’s mausoleum, Samerkand from which my diatom sample was collected and, right, the circular colonies of diatoms on the bottom of the water trough.  The largest of these colonies is about half a centimetre across.

Several freshwater diatoms form conspicuous colonies but what intrigued me about these particular growths was that the colonies were disc-shaped, reflecting horizontal growth with little vertical development.  Once back from my travels, I had a look under the microscope and was surprised to see that they were composed of almost-pure growths of either Achnanthidium minutissimum or a very close relative (my observations were on the vodka-preserved specimens and I have not yet had a chance to look at cleaned valves).   This is an extremely common constituent of biofilms all over the world but I have never seen it forming discrete colonies in this way.  I suspect that, given time, all of these colonies would merge to form a continuous biofilm and that, in a natural ecosystem (rather than a water trough), grazing by invertebrates would then control the biomass so that they formed a subaquatic and microscopic “turf”.   Maybe what I am seeing is the early stage of colonisation in a situation where there are, as yet, no grazers?   It is very hard to tell an ecological story from a single, brief visit to any habitat but that would be my opening gambit.

Microscopic views of Achnanthidium minutissimum colonies from the water trough near Daniyar’s mausoleum, Samarkand, April 2017.  The left hand image was taken at x100 magnification and shows a colony (or fragment) that is about 650 micrometres across.  The right hand image was taken at x1000 magnification.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

Achnanthidium minutissimum was not the only familiar plant (in the broadest sense) that we saw on our travels.   The grazed grassland between Daniyar’s mausoleum and Bibi Khanym mosque, our next objective, contained several flowers familiar from home (see Heather’s blog) and our trip to the Tien’shan mountains a few days later revealed many more, including a steep-sided valley full of hawthorn bushes.   It is a good reminder that, however far from home we are, and however exotic our surroundings, we are still in the broad temperate belt around the Eurasian continent that allows a measure of biogeographical continuity across this area.  Some of the plants we saw in the wild in Uzbekistan are garden plants in north-west Europe (the tulip is a good example) but several others thrive in the wild in both places.

Botanising in the grassland between Daniyar’s mausoleum and Bibi Khanym mosque, Samerkand, April 2017.

Decoration on mausoleums at the Shar-i-Zinda complex in Samerkand, near the Bibi Khanym mosque and Daniyar’s mausoleum.  The photograph at the top of this post shows the exterior of Daniyar’s mausoleum.

Reaching for the stars …

One of the more intriguing characters I discovered during our time in Uzbekistan was Ulug Beg (1394 – 1449), grandson of Timur and inheritor of his empire.   Timur consolidated and expanded the conquests of Ghengis Khan and established Samarkand as the capital for an empire that extended from Turkey to northern India.   Ulug Beg, by contrast, was a more peaceful and intellectual character, more interested in science than statesmanship.   He endowed three Madrassas and stipulated a curriculum that extended beyond studying the Koran and Islamic law to include mathematics and astronomy too.   This is reflected in the decoration of the Ulug Beg Madrassas in both Samarkand and Bukhara which include depictions of the night sky and inscriptions extorting the Muslim faithful to aspire to knowledge.

On a hill on the outskirts of Samarkand, the distant snow-clad peaks of the Pamirs serve as a backdrop to Ulug Beg’s observatory, although all that remains now is part of a huge quadrant arc now largely buried.   Using this, Ulug Beg’s astronomers were able to determine the position of celestial bodies with great accuracy, to work out the tilt of the earth’s axis (23.52 degrees) and calculate the length of a year to within a minute of the best modern estimates.   This was accomplished two centuries before Galileo first pointed his telescope to the heavens and, indeed, without any optics at all.

The quadrant arc at Ulug Beg’s observatory in Samarkand.

His is not the only observatory from the Medieval Islamic world that has survived and I was lucky enough to visit the Mughal observatory, the Jantar Mantar (c. 1724) in Delhi last year.  Unlike the Samarkand observatory this one is above ground and has been restored, giving the visitor a much better sense of the scale of the undertaking.  The observatory at Jaipur is also in good condition and was the subject of a fascinating episode of In Our Time, for those readers who are able to access the BBC’s archives.   These were the most sophisticated scientific instruments of their day; now they stand as monuments before which modern scientists should reflect that Western hegemony of science is a very recent phenomenon.   Ulug Beg’s observatory stands as a reminder of science’s deep foundations in ancient wisdom preserved or discovered on the plains of Central Asia.

The Misra Yantra, part of the Jantar Mantar complex of astronomical instruments in Delhi.

Western astronomy’s paradigm shift occurred when people who were trying to understand the cosmos came into contact with with people with practical skills such as glassmaking (a pre-requisite for optics) and metalworking.   The individual elements were all present in the medieval Arab world but the one-off spark of genius that brought them all together just did not happen.  Glass is the least conspicuous of these components in Bukhara and Samarkand until we looked closely at the tiles which decorate their ancient buildings.  The glazes which gives these tiles their lustrous appearance are made from natural pigments mixed with ground glass (“faïence”); however, there was little evidence of extensive working of glass, so an astronomer would have been highly unlikely to have that serendipitous encounter that would have opened new opportunities. Progress is, we have to remember, often a stuttering series of serendipitous events, very few of which have any lasting impact.

What became of Ulug Beg?  He was murdered by his own son and his observatory was destroyed by religious fanatics.   He was, by all accounts, a better scientist than statesman.   The attention to detail that a scientist needs means taking your eye off the big picture.   Reading between the lines, this was Ulug Beg’s undoing and within a generation Timur’s empire had collapsed into a number of independent Khanates.    Over time, Ulug Beg’s discoveries were assimilated into European astronomical thinking and he and his fellow Central Asian polymaths were gradually written out of Western histories of science.   I’m grateful to a new generation of historians such as Peter Francopan (“The Silk Roads: A New History of the World“, Bloomsbury, 2015) who are giving us a less Euro-centric account of progress.  Compare his approach to that of Kenneth Clark in Civilisation (1969), for whom the term “barbarian” seems almost synonymous with non-European, and then look up at the intricate decoration on Samerkand’s madrassas.   Barbarians?  I don’t think so.

A view of the courtyard of the Ulug Beg Madrassa in Bukhara.   The photograph at the top of the article shows the exterior of the Ulug Beg Madrassa in the Registan in Samarkand.

Synchronicity in Samarkand …

I had intended my next post to continue the story of inorganic carbon in freshwater but a holiday has intervened. However, as is often the way with my travel, I have found some unexpected associations with my professional life.

I had wanted to show, using a graph, how much influence inorganic carbon supply (which freshwater biologists refer to, confusingly, as “alkalinity”) had on the types of diatom that are found in rivers. But the simple act of plotting a graph with Excel had, I realised, some unexpected resonances with my current location in Central Asia. I am in Samarkand, in Uzbekistan, a city with a very long history and which numbers Omar Khayyam (1048 – 1141) amongst its previous inhabitants. Omar Khayyam is best known in the West as a poet but was also a noted mathematician and astronomer. Khiva, another ancient city in Uzbekistan, was the birthplace of Muhammad ibn Musa al-Khwarizmi (c.780 – 850) regarded as one of the founders of algebra. Both, in other words, laid the groundwork for the equation y = mx + c, the equation for a straight line that allows me to express the relationship between the diatom assemblage and alkalinity in quantitative terms.

The relationship between the Trophic Diatom Index and alkalinity in a dataset drawn from UK rivers. More about this will follow in a future post but, for now, it is presented as an example of how biological data often fit y = mx + c, the equation for a straight line (indicated by the red line on the graph)

The point of algebra is that you can work out general principles that apply to a situation regardless of the quantities involved. An equation is simply a means of replacing these quantities with letters or symbols so that you can work out the value of something that you don’t know in terms of things that you do know. One of these ancient mathematicians – we don’t know who, but I am giving Uzbekistan the benefit of the doubt – decided to use the Arabic word “shay” (which means “thing”) to represent the unknown in his equations. When the early algebraic treatises were translated to Spanish in medieval times, “shay” became “xay”, which eventually was shortened to “x”. That, at least, is the legend, and no-one seems to have a better explanation. Whenever we use “x” in an equation, in other words, we should reflect that we are part of a tradition that extends back over 1000 years to the plains of Central Asia.

The straight line equation, however, bucks this neat theory to some extent as, in this realm of algebra, “x” represents the known rather than the unknown entity. The unknown, by convention, is indicated by “y”. “Why “y”?” you might ask and, I am afraid, I cannot help. It may be that there is no sensible explanation (“quarks” are, after all, named after a nonsense word in Finnigan’s Wake) but the etymology of “x” is, you have to admit, too good to waste. Especially when writing from Samarkand.

Timurlane’s tomb (Gur-i-Amir) in Samarkand. The photograph at the top of the post shows part of the Registan madrasah complex.

And, finally, I could not resist including this image of decoration on the Sher Dor Madrassa at the Registan: evidence that Medieval Islamic scholars knew about centric diatoms?

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