Disaster theories

Did you know that I collect volcanoes?

I wrote this some years back, but it remains relevant.

One of the hallmarks of popular science is the disaster scenario, because it sells well. Sometime, though, the scenarios are popular, but not science. Let us consider the view that asteroid strikes cause volcanoes to erupt.

The world’s flood basalt provinces are the remnants of the largest eruptions of lava on Earth, with known volumes of individual lava flows exceeding 2000 cubic kilometres. By comparison, the ongoing eruption of Kilauea volcano on Hawaii has produced just 1.5 cubic kilometres in 16 years!

The very largest are the Deccan Traps and the Siberian Traps (‘trap’ in this case is a Sanskrit word meaning ‘step’, because of the way the flows weather and erode later to produce stepped hillsides). The Columbia River flows shown above are rather smaller.

A number of the flood basalts formed at times close to the occurrence of certain extinction events, in particular the Newark outpouring of a million cubic kilometres, some 201 million years ago; the Deccan outpouring of perhaps 2 million cubic kilometres, around 66 million years ago; and the Siberian outpouring, also of some 2 million cubic kilometres, around 249 million years ago.

The Deccan outpour lies close to the Cretaceous-Tertiary, at the time when the dinosaurs all died, and the Siberian event matches closely the Permian-Triassic boundary, while the Newark event matches the end of the Triassic.

The probability of having three major volcanic events that would each typically last about a million years should occur within 1 million years of major extinction events during the last 250 Myr (of which there are about 12) is about one in ten thousand.

This has tempted many in the past to assume that these volcanic outbursts were responsible for the extinction events, and when an asteroid in Mexico was associated with the Cretaceous-Tertiary extinctions, some vulcanologists argued that the impact of the asteroid must have triggered the basaltic flow.

How serious would such an event be? The only flood basalt eruption since written history began was the 1783-84 eruption of Laki in Iceland. This produced a basaltic lava flow of 565 cubic kilometres, which represents only 1% of the volume of a typical large igneous province (or LIP) flow, but the eruption’s environmental impact resulted in the deaths of 75% of Iceland’s livestock and 25% of its population from starvation. If such a relatively small eruption happened today, all air traffic over the North Atlantic would probably be halted for three to six months.

So it seems possible that an eruption bigger than that would be enough to possibly trigger an extinction event, but all the same, the idea that volcanoes can erupt when the Earth is smacked by a large comet or meteorite has become a popular idea in geology. That may be so, but it seems there is no proof to back the claim up.

Not only is there no firm evidence that an impact started a volcanic eruption on Earth or on any other planet, there is no known mechanism by which this can occur. According to Jay Melosh who had studied the matter closely:

This idea probably got its start in pre-Apollo days when early observers of the moon noted the common occurrence of dark material — usually supposed to be lava — filling the nearside impact basins. A logical inference is that this is a genetic association: the impacts caused lava to upwell in the biggest craters after they had formed, eventually filling them.

This view should have collapsed in 1965, when the Russian probe Zond 3 made good photos of the lunar farside that showed that the farside basins are not filled with basalt. Moreover, the samples returned from the moon by the Apollo missions showed that the mare basalts are considerably younger (up to about 1Gyr) than the basins in which they lie.

The main point Melosh makes is that there seems to be no way that the impact of an asteroid could punch a deep enough hole to let all that basalt out: “Even in the 100-km (transient) diameter Chicxulub crater, the Moho beneath it is barely disturbed, with less than a few km uplift beneath the centre. Under these circumstances pressure relief melting seems very unlikely, even in the largest known terrestrial craters.”

So exciting as the scenario may be to movie makers, it seems to be an idea without legs, and that isn’t all the bad news for those who enjoy a bit of doom and gloom.

The pendulum and the shape of the planet

The 'researchers' of the Internet, the climate clowns who cherry-pick data to prove their dopey obstructionist theories, commonly demonstrate how little they know of the ways that scientists can measure and discover things.

With the exception of the Flat-Earthers (and even climate clowns hate it when they are treated as latterday Flat-Earthers!), we all believe that the Earth is pretty much a sphere, but pretty much leaves wiggle room, and strange as it may seem, it was an upgraded version of a playground swing that revealed the precise shape of our globe, which some people likened to a watermelon stood on end, while others thought was more like a pumpkin.

This is the story of how they did it, almost three centuries ago.

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In some parts here, the main measurements have been converted to their modern equivalents. The unconverted unit called the ‘line’ is 1/4 of a barleycorn, a twelfth of an inch, or about 2 millimetres.

The barleycorn measurement turns up in the oddest of places. Edward I, King of England, decreed in 1305 that “three grains of barley, dry and round, make an inch”, and if you change from a size 7 shoe to a size 8 shoe, the difference in length is one barleycorn.

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Now to our story:

In 1672 Jean Richer reported that the period of a pendulum varied with latitude, and Isaac Newton said that Richer’s variation of pendulum was due to equatorial bulge, a comment offended the French. By this time, nobody thought the world was a perfect sphere any more, but France and England disagreed, and national honour was at stake.

Isaac Newton had proposed that the Earth was an oblate spheroid. If this were so, argued Newton, the precession of the equinoxes (we may or may not come to those later) could be explained. French scientists had taken some sloppy measurements, getting results which suggested that the Earth was more like a watermelon on its end than a pumpkin.

The French Académie set out to determine the truth of the matter by experiment, measuring a degree of latitude in Lapland and in Central America. Among those who went to Lapland was Pierre de Maupertuis, while the American group included Pierre Bouguer and Charles La Condamine.

Richer’s pendulum clock had been accurate in Paris but it lost two and a half minutes each day at Cayenne in Africa, closer to the equator. Clearly, more data were needed, and scientists were rushed to different places in 1735, mainly in South America, a mere 63 years after the comment. Newton had died in 1727, but the French still wanted to show him up, the insolent upstart!

We know Pierre Bouguer’s name today mainly in the form of Bouguer anomalies. This name commemorates his pioneering work in the Americas. When the acceleration due to gravity is measured very accurately, small local fluctuations can indicate equally local deposits of high or low density mineralisation — these fluctuations are the Bouguer anomalies.

Bouguer spent much of his life studying gravitational effects. In 1740, he estimated the value of G, the universal gravitational constant, using a mountain as an attracting mass. A method such as this can only be as accurate as the information the enquirer has about the interior of the mountain, and there were other problems which Bouguer could not have known about. We will ignore those for now, but the key word is isostasy, if you want to know more.

The French work in Central and South America between 1735 and 1743 was to measure the length of an arc of one degree of latitude at the Equator. Other scientists went to Lapland to measure a close-to-polar degree. Any difference in the lengths would reveal whether France or Britain had the right shape.

Inserted without comment.

Here, from the French Académie des Sciences Memoirs, is part of a letter from Bouguer to René de Réaumur in 1735, followed by part of Bouguer’s 1749 report of his findings.

I have made here [in San Domingo] a simple pendulum of steel which I have made as invariant as possible. It has a bob of [12 kilograms], about [12 centimetres] in diameter and [3 centimetres] deep. To keep it swinging true, I have put on the rod a crossbar of iron to serve as an axis, at right-angles to the rod. The instrument is mounted on a tempered steel knife-edge on two steel springs. These two springs are mounted on a copper plate in which there is a hole for the rod. The plate rests on a stool [1.5 metres] high, and is levelled by three screws…

We used the barometer that we set up to study the balance between the weight of the mercury and the air in all the accessible parts of the atmosphere. We saw how many feet we had to rise or descend to make the mercury change height by one line. It is then necessary to find the specific weight of air that balances other bodies. In this way, I have found by comparison with copper that on the top of Pichincha, there is a loss from unity of 1/11 000. Now it follows that the weight of my simple pendulum also loses 1/11 000 part of its weight. This loss produces a similar reduction in the restoring force, and naturally, I found the pendulum to be slow by 1/11 000. To correct this loss, it was necessary to adjust the pendulum’s length by 4/100 of a line…

Translation of the translation: Bouguer had an accurate pendulum, mounted on a wooden stand (the stool) and it was adjustable. He used a barometer as a way of measuring altitude. By timing the pendulum, he could get a measure of g at different heights above sea level.

The degree-measuring expeditions succeeded in proving Newton correct, but one of the more lasting effects came from La Condamine’s explorations while he was there, travelling over a large part of South America, and then 5000 km down the Amazon.

When he returned to Europe, La Condamine brought with him what the locals called cauchu, and the French still call caoutchouc. Thanks to Joseph Priestley, we still call it ‘rubber’, because it can be used to rub out pencil marks, and what is an eraser in some English-speaking countries is still called a rubber in others.

Benham's colourful tops.

 Charles E. Benham (1860-1929) was a journalist and inventor, and he deserves more than this, or what his Wikipedia entry, offers. I was triggered to go here this morning because of a comment Stew made about my last entry: there may be more, later.

When I first discovered the Benham disc, I was delighted, because I am colour-blind. The Benham disc is a black and white patterned circle, which looks coloured when it is spun around. I had heard of these things but I had never tried them, and I thought it would be interesting to see whether they had the same effect on a colour-blind viewer. Being colour-blind does not mean that you “see everything in black and white”, as David Brewster said. It simply means you see colours differently. It occurred to me to wonder if maybe I would see different colours in the disc from those other people see.

Benham described his illusion in an article published in Nature  back in 1894. In those days, if you wanted to see the disc, you would look for the design on a children’s top, known, predictably, as ‘Benham’s top’. The first account was a brief and anonymous one, noting that the ‘disc’ on the top was a black semi-circle, with the white half of the circle divided in four, and with black arcs painted in.

As the disc is rotated, people see different colours from the different black arcs. And, as the reporter noted, if “. . the direction of rotation is reversed, the order of these tints is also reversed. The cause of these appearances does not appear to have been exactly worked out.”

An ‘Artificial Spectrum Top’, devised by Mr. C. E. Benham, and sold by Messrs Newton and Co., furnishes an interesting phenomenon to students of physiological optics. The top consist of a disc, one half of which is black, while the other half has twelve concentric circles drawn upon it. Each arc subtends an angle of forty-five degrees. In the first quadrant there are three such concentric arcs, in the next three more, and so on; the only difference being that the arcs are parts of circles of which the radii increase in arithmetic progression. Each quadrant thus contains a group of arcs differing in length from those of the other quadrants. The curious point is that when this disc is revolved, the impression of different colours is produced upon the retina.

(Nature , 51 (1309), November 29, 1894, 113–114.)

There followed an animated correspondence, during which Benham stepped in. Illuminate the top with a bright sodium flame, he said, and you will see a very clear blue, and a very clear red. And now the controversy heats up: immediately underneath, in the same issue, Professor Liveing retorts that he has seen no such colours: the phenomenon is obviously a subjective one. Clearly there is room for more research here.

It is unclear whether Nature  thought so too, for they go on in the same column to publish next a letter from F. G. Donnan in Leipzig, suggesting that we need a new word in chemistry: ‘solute’, and the discussion seems to have died there. Well, as far as I can judge, I see the same colour effects as other people, which means we won’t learn anything about colour blindness from the Benham disc. But how about trying to learn about colour vision? What causes the colour effect as the disc slows down?

Most explanations seem to speculate rather than to explain, but here is the official version as found in psychology text-books. We have three kinds of light receptor in our eyes, in the same way there are three kinds of phosphor in a colour TV. Speaking crudely, these receptors, the cone cells, are all sensitive to just one of red, green and blue.

According to the theory, you need all three kinds of cone in the retina of your eye to see colours normally. Somehow, the cones which pick up one of the colours (red, for example) must react differently to flashing lights of a particular frequency. So with different size black bits on the disc, we get different frequency effects, and so our eyes are stimulated to ‘see’ different colours.

Well, that’s what the theory says. Some time in the future, a careful and critical look at it, will reveal once and for all whether and how this official explanation operates, and where it breaks down. There is probably a Nobel Prize in this for somebody, though they will need to acknowledge Gustav Fechner, and that's a hint.

The Birmingham Lunar Society

Once upon a time, they say, there was a wonderful Golden Age of scientific communication, an age when the most prominent scientists and admiring lay-people were in frequent contact, either with each other, or with each others’ works. To exist at all this age probably had to await the development of the railway, the telegraph, and machine type-setting.

I suspect this Golden Age came at the absolute height of public scientific interest and endeavour, a time when scientific creativity was pouring out all over the place, and discoveries sparked off other discoveries, almost at the speed of light. All that was required was the transmission of the original idea.

Calculating what destroyed the Golden Age is harder: it might be sufficient to blame television, but the era probably died earlier than that. Maybe there never was any Golden Age of science communication at all. One thing is certain, though: there was a definite Dark Ages for scientific communication, and they died out around 1800, when scientific journals were first published, including the journal which nearly robbed Alessandro Volta of his rightful credit.

If you were a scientist in provincial England in the late 1700s, or worse yet, in colonial Australia, tidings of new discoveries were an unconscionably long time coming, and much of the news came only in the form of private mail. This helps to explain why so many scientists banded together to share their news, but what I find harder to explain is why a few of these groups were so hugely successful. Groups like the Lunar Society of Birmingham, for example.

The ‘Lunatics’ got their name from their solution to the risks of travelling the dangerously rutted roads around Birmingham to get to their meetings. It was unsafe to travel those roads in the dark of a moonless night, so they would meet on the night of the full moon. The real problem with Birmingham was that it might have been a good place for building a factory, but it was the most dreadful starting place for a trip to London.

It wasn’t much better for getting to Edinburgh from either, the city where so many of the members had learned their science. They might as well have been in the colonies! For any sort of intellectual stimulation, they and their friends had to rely on what came to hand in their home town, or near to it.

They were a tightly interlinked and brilliant little group, and the Royal Society in London had nothing on them. The Royal Society’s members were a bunch of dullards and dilettantes by comparison. Upper Class twits, Tories, that sort of thing, nothing like the Birmingham mob at all.

And that brings us to one of the problems with the Birmingham Lunatics: they were seen as a mob of radicals, people who felt American and French Revolutions were Good Things and said so, which wasn’t a good idea, for the spirit of a former-day Senator McCarthy was alive and well in eighteenth century England.

At one point, the mob even burned down Priestley’s house to show what they thought of him. If ‘Congreves’ (the matches, that is, named because, like the incendiary rockets of Sir William Congreve, they set fire to things) had been invented back then, they might have got Joseph Priestley as well, but they had to send off for ‘some fire’, and Priestley made his escape. Recall, though, that while the members called themselves ‘Lunatics’, it was a real lunatic, Farmer George, King of England, who tried to get the Royal Society to reverse its stand on lightning rods, simply to contradict the American rebel, Benjamin Franklin.

You will find this story elsewhere. To its credit, the Royal Society refused the King’s demand, but Farmer George would never have tried the same stunt on the Lunar Society of Birmingham. After all, one of their corresponding members was that same villainous Ben Franklin, and one of the Society’s sources of inspiration (some call him a founder), William Small, had been the teacher of Thomas Jefferson in America, and had now come to Britain.

The other founders included a country doctor, Erasmus Darwin, who is fairly well-known as grandfather to Charles Darwin, but Erasmus was quite an intellectual giant in his own right. As we have seen, long before Charles got into the evolution business, Erasmus had proposed a Lamarckian sort of evolution, beating Jean-Baptiste de Lamarck to the idea by a number of years.

Charles’ other grandfather, Josiah Wedgwood was a member as well. So was William Withering, who discovered that the foxglove plant contained a steroid substance which we call digitalis, and use for heart disease.

It didn’t take long for other members to come rolling up, and the effectiveness of such a society soon became obvious. This was a time of breakthroughs and new ideas, a time for rapid development. It was also a time of simple apparatus to measure the extents of simple principles, so almost any participant could experiment further.

As I mentioned, they were mostly trained at that cradle of scientific education, the University of Edinburgh, and many of them were involved in manufacturing, so new problems arose quite frequently, nice knotty problems for the others to tackle.

But what would it take to establish a similar Golden Age of science and science communication and application today? Was there a magical formula, or was it just good fortune that so many people came together and sparked off each other? Was it because they were elitist, or only attracted an elite? As newsgroups, fora and email lists develop and mature on the Internet, will they begin to fill that role?

Only time can tell — but I think the email list is already dying away.

Water wheels

Left, an overshot waterwheel in Poland, right, an undershot waterwheel, Den Gamle By, Denmark.

The water wheel was the start of a whole, and rather serious set of simple machines, devices that used power. The water wheel gave more power more cheaply (once a mill was built), it helped feed a lot of people, but more importantly, it set people to thinking about the mechanical works of a mill.

Water mills probably started in Greece, some time before 80 BCE, because that was when a Greek poet called Antipater of Thessalonika mentioned young women being relieved of the work of operating a hand-mill, now water had taken over the hard work.

Soon, waterwheels began to spread into other areas where there was plenty of rainfall, all year round, places where slaves were hard to get. It was the first labour-saving device. The water wheel may have got its start, though, as a device used to raise water from a river to fields, high above the river bank, and that requires some explanation.

Today, if a moored paddle steamer sits in a current and the paddle wheel is disconnected from the engine, the wheel will turn. Something similar would happen to a water-raising wheel (usually powered by humans, working it as a treadmeill) when it sits in the current of the river. This is the simplest of water wheels, the undershot wheel, where water passes under the wheel, making it turn.

Then there is the more efficient overshot wheel where water drops onto the front side of the wheel and carries the front of the wheel down. Both the undershot and overshot wheel need at least two gear wheels to transfer the rotation through 90°.

Waterwheels were not as good at gathering energy as the efficient turbines in modern hydroelectric stations. Still, when there were no animals to feed, all you had to do was have a big enough mill, and enough fall to get enough energy from it.

This was a special problem with overshot wheels, where mill owners needed to take water out of the river, somewhere upstream, and run it through a channel that wound around the contours on a gentler gradient than the river bed.

Sometimes this would be helped out by a weir or a dam that raised the water level, but if there were several mills along a river, they would sooner or later start to interfere with each other. The Domesday Book was completed in England in 1086. This inventory of what the Normans had taken when they invaded England listed 5624 waterwheels in England, about one for every 50 households.

Bread was a staple food, and so mills were needed, all over the country. The Domesday book also records two mills in Somerset which paid their rent, before 1086, with blooms of iron, which makes it fairly clear that those mills were being used to forge iron. 

Cistercian abbeys in 12^th century France commonly used waterwheel power to grind grain, to sieve flour, to full cloth and to tan leather.

At other times, water power crushed olives and operated bellows for forges and the fires used to brew beer. A paper mill powered by water existed in Spain in 1238, and seven such mills were to be found in Italy by 1268. Paper was made by pounding linen, either by hand, or by foot, or by water power. Guess which one was more popular with the workers?

Water power was easier. when you could get it. In France, a tributary of the Seine River, the Robec, had two mills in the 10^th century, four in the 11^th, ten in the 13^th and twelve at the start of the 14^th century. Before long, the medieval world was running out of space for mills, and disputes began to break out as dams and weirs grew higher, backing water up to the next dam upstream, reducing the fall at the upper dam.

At peak times, the Garonne River at Toulouse in France has a flow of up to 9000 tons of water a second, about a fifth of a cubic mile or 780 megalitres of water a day. Damming something like that meant driving thousands of 6-metre oak logs into the river bed in two rows and then filling the gap between with rocks, gravel, oil and wood to make a water-tight wall.

There were three Garonne dams: Château-Narbonnais, La Daurade and Le Bazacle, and between 1278 and 1408, various acts of dam-raising led to lawsuits and orders to demolish dam extensions and pay damages that were mostly ignored. By 1408, the La Daurade company had ceased to exist, its last shares snapped up by the shareholders of Le Bazacle, ending the dispute.

In later times, windmills took over part of the task, simply because they could be located where there was no reliable flow of water, but windmills were not as powerful. The early Industrial Revolution grew up near rivers, but with time, the waterwheels were replaced by steam engines. The world was ready for them, because the mechanical skills needed to build and fix mills driven by water and wind were very much the skills needed to make early steam engines.