Sunday, February 13, 2011

Benjamin Franklin, Thomas Chamberlin, and the circulation of the oceans.

Benjamin Franklin made the first widely publicized contribution to knowledge of ocean circulation. He was inspired in this by his stay in Paris during the summer of 1783---a summer of busy negotiations, but also one in which he observed the 'volcanic fog' from the eruption of the Icelandic volcano Laki--and experienced the exceptionally severe winter of 1783-1784 back in the USA. Could large volcanic eruptions cause dust clouds big enough to cool the Earth temporarily? Franklin thought so---and expanded on his ideas about weather and climate in a speech he gave in 1784 titled 'Meteorological Imaginations and Conjectures' which he later submitted as a paper to the Memoirs of the Literary and Philosophical Society of Manchester where it was published in pages 373-377 in their 1789 folio.

Of more relevance to the topic of ocean circulation, Franklin wrote the first serious scientific paper about ocean circulation in 1786 which he submitted to the American Philosophical Society . Google has a link to it, but none of the pages are up. I'm linking anyway hoping that his article is added later.

Maritime Observations, the title of Franklin's monograph, is mostly about the Gulf Stream. Mariners had known about ocean currents for centuries, but Franklin was the first to write about them in a science publication that got wide circulation--therefore making the topic 'stick' in the scientific community. Franklin was the first to give the Gulf Stream credit for Europe being so mild when it was so far north--Paris being further north than Montreal, and Great Britain and Ireland at the latitude of Labrador. He got the broad outline of the North Atlantic surface ocean circulation right--the trade winds pushing the tropical waters west, where they entered the Caribbean and Gulf of Mexico, turned north off the coast of the eastern United States, and then northeast towards Europe, carrying warmth.

It is interesting to read accounts from the first settlers in the 1600s about the weather. New York and Boston are at the latitude of central and southern Italy, and Jamestown is at the latitude of Gibraltar. Colonists were shocked to discover that it "freezes and snows severely in winter".

This was noticed and discussed by scientists in the 17th and 18th centuries, and before Franklin it was believed that forests kept places colder---that snow lingered in the shade of trees and kept the land colder as a feedback. Thomas Jefferson had written that as the land was cleared and the forests replaced by fields and towns, that American would get warmer---the widespread belief of educated people in the 1700s. We know now that was wrong.

For the next hundred years---what else was added to knowledge of the ocean circulation system? Not much (and truth be told, the oceanographic expeditions of the late 19th century and early 20th century didn't add much knowledge either) But there was one expedition that generated some interesting ideas.

The Challenger Expedition was perhaps the greatest scientific expedition of the 19th century. It went world-wide travelling more than 70,000 nautical miles (80,000 statute miles), the longest scientific journey undertaken to that point. Not until astronauts went to the moon and retrieved moon rocks did a scientific expedition travel further. Before Challenger, people had only observed the top few fathoms of the ocean.

To enable her to probe the depths, the Challenger's guns were removed and her spars reduced to make more space available. Laboratories, extra cabins and a special dredging platform were installed. She was loaded with specimen jars, filled with alcohol for preservation of samples, microscopes and chemical apparatus, trawls and dredges, thermometers and water sampling bottles, sounding leads and devices to collect sediment from the sea bed and great lengths of rope with which to suspend the equipment into the ocean depths. Because of the novelty of the expedition, some of the equipment was invented or specially modified for the occasion. In all she was supplied with 181 miles (291 km) of Italian hemp for sounding, trawling and dredging.

Challenger returned to Spithead, Hampshire, on 24 May 1876, having spent 713 days at sea out of the intervening 1,606.[1] On her 68,890-nautical-mile (127,580 km) journey,[1] she conducted 492 deep sea soundings, 133 bottom dredges, 151 open water trawls, 263 serial water temperature observations, and discovered about 4,700 new species of marine life. Copies of the written records of the Challenger Expedition are now stored in several marine institutions around the UK including the National Oceanography Centre, Southampton and the Dove Marine Laboratory in Cullercoats, Tyne and Wear. The complete set of reports of the Challenger Expedition, written between 1877 and 1895, are available online at

Given the achievements of the Challenger Expedition, it is perhaps a bit harsh to say that knowledge of the deep ocean was not advanced very much. It did expand knowledge many times over, but from virtually nothing to very very small. It did make many interesting observations.

The most important was that globally, the deep oceans more than a few hundred yards down are very very cold. Close to freezing. Everywhere. And that most of the cold water in the deep oceans originated from the margins of Antarctica. Cold, oxygen-rich water sank near Antarctica, and to a much lesser extent near Greenland and in the Arctic Ocean. After analyzing the observations, it was believed that water rose near the equator where solar heat warmed the waters and currents flowed poleward to balance the cold water sinking.

The Challenger expedition discovered another interesting feature. The Mediterranean Sea is considerably saltier than that world ocean (part of the reason why the Atlantic is saltier than the Pacific) and this warm salty water sinks about 5,000 feet to form a distinctive and identifiable layer throughout most of the Atlantic!

That the Atlantic is saltier than the Pacific and Indian Oceans was something of a surprise, given that such huge rivers drain into it. The Amazon river of course, and the Congo river. The Parana river system. The Mississippi river is only 4th!

On the west coast of the Americas, the Columbia River is the only sizable river. In East Asia, the Amur, Yangtze, and Mekong are major rivers, but the whole flow from East Asia is smaller than the Amazon alone. Australia contributes almost nothing to the Pacific.

Even stranger, the Arctic Ocean is really an arm of the Atlantic, and receives several large Rivers in the Russian Arctic--the Ob, Yenisey and Lena rivers--and the Arctic is the least salty of all oceans and mixes freely with the Atlantic. The Mediterranean inflow explains a little of the difference, but only a few percent. The salty Atlantic was not explained until the 1960s.

The deep warm water layer from the Mediterranean interested an American geologist, Thomas Crowder Chamberlin. Chamberlin (1843-1928) was an interesting person---together with astronomer Forest Ray Moulton he crafted the Chamberlin-Moulton planetesimal hypothesis to how the solar system formed--two suns nearly colliding and ripping off solar material which condensed into planets. He believed solar systems were very rare, since such stellar near collisions would be very rare--and calculated that our sun and the other sun in the near collision might have the only solar systems in the Milky Way's galactic arms! That hypothesis was wrong, but Chamberlin did make a lot of valid contributions to geology.

In 1904, he was going over the Challenger Expedition results, leafing through them. The Mediterranean water layer struck him. The Atlantic was already saltier than the rest of the oceans--what if it got saltier? If a local climatic change decreased the flows of the Amazon and Congo rivers, what would happen then?

Chamberlin thought that the tropical oceans would get so salty that the whole ocean circulation system would flip. Instead of cold water sinking near the poles, warm, but very salty water would sink in the tropical Atlantic, and instead of warm surface currents flowing north, cold currents like the Labrador current would flow much further south, cooling the climate and triggering an ice age!

Chamberlin thought that it would work like this. The sun heats the equatorial regions most strongly during the equinox when it passes overhead at noon. The equator gets less sun during the solstices, even though the day length stays the same. Chamberlin thought that when the precession of the equinoxes caused the sun to be closest to the Earth near the solstice, rainfall would decline with less convection triggered, causing the Amazon and Congo river flows to decline, which would cause salinity to increase--the Gulf stream to collapse, causing more cooling, and the cooling would trigger ice sheet formation, cooling the whole world, and cooling the tropics, making the tropical water less prone to evaporate, making the tropics drier, and the tropical water even denser--in a feedback.

The feedback would be broken when the sun was closest to the earth during the equinox again, and trigger more convection, triggering more rainfall, triggering more river flows, lowering the density of the tropical oceans, stopping the sinking of the tropical oceans, and letting the Gulf stream flow again, and the whole feedback operating in reverse.

Chamberlin's ideas triggered a lot of discussion when they were published in 1906. He was known for coming up with wild 'out there' ideas like his solar near collision hypothesis, and tossing them out into the scientific community to be discussed and picked apart. But triggering questions and research.

Having ice ages triggered by changes in tropical rainfall and ocean currents was an original idea, and was a good reminder that ice ages are global phenomena, and that their causes and triggers might be found outside the polar regions.

Chamberlin's ocean circulation reversal idea is wrong on several points, but it did generate for a time some interest in researching how ocean circulation works and how it changes---and how that might impact the climate.

Unfortunately, technology for detailed mapping of the ocean circulation system was not available 100 years ago. There were some proposals for new expeditions, using submarines this time to help map the deep ocean circulation system (which the Challenger Expedition did not have the technology to map---it generated hypotheses and some information on the cold state of the deep ocean, but no answers). But World War I brought an end to those ideas, and after World War I the idea was no longer in fashion, for whatever reason. The Chamberlin hypothesis faded away.

Chamberlin's hypothesis had one glaring fault. Evaporation and rainfall is a circular process. Water evaporating from the tropical Atlantic falls back into the sea, or flows back in rivers. Increasing the evaporation rate increases river flow back into the Atlantic. Decreasing the evaporation decreases the river flow back. It doesn't change the salinity appreciably.

But Chamberlin was the first to hypothesize that the ocean circulation system can have a big impact on climate. And it was an original idea--unlike ice ages and greenhouse warming, which have many fathers, going from person to person and being strengthened---he thought of this all by himself. No one had thought of it before.

Wednesday, February 9, 2011

Svante Arrhenius part 2

Arrhenius had some good data to observe. It had already been noted by Frank Washington Very and Samuel Pierpoint Langley that the infrared radiation from the moon which was observed at the surface of the earth changed its characteristics according to the angle of the moon above the horizon. These observations agreed with the properties of infrared absorption by carbon dioxide observed by Tyndall. (This also had a very important implication, which was missed by everyone, including Arrhenius, for more than 50 years after Arrhenius published his greenhouse theory. More on this later.)

Arrhenius also had a new analytical tool--the Stefan-Boltzmann law which had been deduced by Jožef Stefan in 1879, with some refinements added in 1884 by his student Ludwig Boltzmann. Arrhenius needed these mathematical tools to do his calculations. In theory, it was simple to calculate. Arrhenius was smart enough to realize it would not be so simple.

Aside from the stress coming from his divorce, which his wife Sofia Rudbeck was making as difficult as possible (this being the late 19th century, when divorce was strongly frowned upon and scandalous in itself) and teaching students and grading papers, which Arrhenius could do on autopilot, there was not much else to do. Arrhenius threw himself into the problem.

First he formulated his 'greenhouse law' (which still stands the test of time.)

If the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression.

This simplified expression is still used today:

ΔF = α ln(C/C0)

In short, each doubling of carbon dioxide in the atmosphere increases global warming by the same amount. A rise from 300 ppm to 600 ppm will increase global temperature the same amount as a rise from 600 ppm to 1,200 ppm will.

Arrhenius also took into account the effect that decreased snow cover would have on the albedo (reflectivity) of the Earth--showing how the feedback of decreased snowcover (or increase if carbon dioxide declined and the temperature fell) would augment the effects of changed in the carbon dioxide concentration. Arrhenius also took into account the effect that a warmer atmosphere would have on water vapor in the atmosphere---a warmer atmosphere could hold more water vapor--and water vapor is a potent greenhouse gas in itself. Figuring out how these feedbacks would augment each other was complex. He spent all of 1895 in tedious calculation, which gave him something to do while going through his divorce, and published On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground in the London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science in the April 1896 issue here.

Arrhenius' theory of anthropogenic global warming made a big splash. It was vigorously debated at the time (and still is, of course.) Knut Ångström made a strong criticism using the results of his experiments on the absorption of infrared radiation by carbon dioxide--which indicated that carbon dioxide was at a high enough level already that it absorbed all the infrared radiation that it could. Ångström and Arrhenius battled it out, but most physicists considered the Ångström criticism to be valid.

It later turned out that while CO2 absorbs all the IR radiation it can in two bands, CO2 absorbs in other bands as its concentration increases. Ångström had made his measurements with accurate equipment, but in a laboratory at room temperature. He didn't try matching the conditions one would see in the polar or upper level environments. As it turns out, in the polar regions and at dry mid and upper levels of the atmosphere there is not enough CO2 to absorb infrared radiation even in the two primary bands.

And there was another clue, staring people in the face---although no one realized it for over 50 years. When Frank Washington Very and Samuel Pierpoint Langley took their measurements of infrared radiation from the moon, the absorption increased when the moon was close to the horizon, and decreased when it was high in the sky. That showed right there that the absorption of infrared radiation was not saturated---otherwise it would have been the same---saturated in every direction equally! But no one realized this!

Arrhenius fought Ångström hard on the infrared absorption issue, but there was another problem. The ocean is alkaline, and was believed to absorb CO2 (carbonic acid) efficiently. In other words, we could emit CO2 into the atmosphere, but it would be mopped up in the ocean. The chemistry of the ocean was being determined and it was apparent that there was about 50 times as much CO2 in the oceans as in the atmosphere. Surely the ocean could absorb what CO2 we emitted easily!

Arrhenius was doubtful about that---although he admitted the oceans could have a buffering effect. Arrenhius' main arguement was that the oceans would not absorb CO2 immediately---and there was also the fact that despite the oceans are alkaline, there is still CO2 in the air? Why wasn't all atmospheric CO2 absorbed completely?
There must be some mechanism that keeps CO2 in balance and prevents its complete absorption by the oceans. And that mechanism could prevent all additional CO2 mankind emitted from being absorbed by the seas.

But this was a weak argument without chemical knowledge and proof of such a buffering effect, and Arrhenius knew it. Arrhenius had strong support from Alfred Wallace in that there must be a buffering effect from the sea, despite the seas' alkaline nature. But it was not until the late 1950s and early 1960s that the buffering effect was shown to exist---and that came about because the rising CO2 levels documented by Charles Keeling in the first few years of his measurements defied explanation otherwise. (there was some work in the late 1950s that suggested that CO2 absorption by the oceans was buffered, but it was not until Keeling's graph that a strong research effort was done).

Arrhenius also publicized another radical idea--panspermia---the spread of life from planet to planet by spores. As is usually the case, panspermia was an idea that had been kicked around by others before him---but as a speculative idea--not as a serious one. He first wrote about panspermia in 1903, and made it a major part of his book for educated popular audiences, Worlds in the Making--the Evolution of the Universe The original English translation is from 1908 (which I have linked). The translation is a bit rough and stilted, since the book was originally published in Swedish as Världarnas utveckling in 1906 and translated into German as Das Werden der Welten (1907). The English translation is from the German--and it would be interesting to see if the book is available translated directly into English in more modern language. We could get Grothar on it ;)

Worlds in the Making--the Evolution of the Universe
also talks about the anthropogenic greenhouse effect. Some extracts follow:

"To a certain extent the temperature of the earth's surface, as we shall presently see, is conditioned by the properties of the atmosphere surrounding it, and particularly by the permeability of the latter for the rays of heat." (p46)

"That the atmospheric envelopes limit the heat losses from the planets had been suggested about 1800 by the great French physicist Fourier. His ideas were further developed afterwards by Pouillet and Tyndall. Their theory has been styled the hot-house theory, because they thought that the atmosphere acted after the manner of the glass panes of hot-houses." (p51)

"If the quantity of carbonic acid in the air should sink to one-half its present percentage, the temperature would fall by about 4°; a diminution to one-quarter would reduce the temperature by 8°. On the other hand, any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4°; and if the carbon dioxide were increased fourfold, the temperature would rise by 8°." (p53) [these are degrees Celsius, not Fahrenheit]

"Although the sea, by absorbing carbonic acid, acts as a regulator of huge capacity, which takes up about five-sixths of the produced carbonic acid, we yet recognize that the slight percentage of carbonic acid in the atmosphere may by the advances of industry be changed to a noticeable degree in the course of a few centuries." (p54)

*note--it turns out that the oceans absorb only half of CO2 we emit, not 5/6ths

"Since, now, warm ages have alternated with glacial periods, even after man appeared on the earth, we have to ask ourselves: Is it probable that we shall in the coming geological ages be visited by a new ice period that will drive us from our temperate countries into the hotter climates of Africa? There does not appear to be much ground for such an apprehension. The enormous combustion of coal by our industrial establishments suffices to increase the percentage of carbon dioxide in the air to a perceptible degree." (p61)

The last quotation from Worlds in the Making--the Evolution of the Universe, seen below, is interesting. Arrhenius thought that the anthropogenic greenhouse effect would be a benefit to mankind. Vast areas of Canada and Russia would be open to cultivation. Arrhenius correctly predicted that global warming would be more pronounced at the poles than in the tropics, so tropical life would not be affected greatly, he felt. The consequences of ice sheet melt and sea level rise do not seem to have entered his mind. Perhaps it was two factors that limited his foresight.

First, he was a Swede. Sweden is a cold place, where summers are pleasant, brief, and looked forward too. Arrhenius thought that places like Sweden would benefit from global warming.

Second, Arrhenius seriously underestimated how much the consumption of coal would increase---and he ignored oil and natural gas, which were not being used much at the time. By the 1890s, we knew about how much CO2 was in the air---measurements had narrowed it down to between 250 ppm and 350 ppm---300 ppm was what Arrhenius estimated. And that figure was close to correct at that time. However, by missing the growth in the consumption of fossil fuels, Arrhenius underestimated badly how rapidly CO2 would rise. He thought it would take 3,000 years for CO2 to double to 600 ppm. Instead we will do it before the 21st century is over--less than 200 years. A period of 3,000 years would be easier to adapt to, with so much more time. And as it turned out, Arrhenius was right about the oceans not absorbing all the CO2 humankind emits. But he underestimated there too. The oceans absorb only half the CO2 we emit, not 5/6ths. But we need to give Arrhenius credit for realizing that not all CO2 that we emit would be absorbed by the seas.

The last quote is below:

"We often hear lamentations that the coal stored up in the earth is wasted by the present generation without any thought of the future, and we are terrified by the awful destruction of life and property which has followed the volcanic eruptions of our days. We may find a kind of consolation in the consideration that here, as in every other case, there is good mixed with the evil. By the influence of the increasing percentage of carbonic acid in the atmosphere, we may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the earth, ages when the earth will bring forth much more abundant crops than at present, for the benefit of rapidly propagating mankind." (p63)

It has to be said that Arrhenius was not a person with great integrity. In 1900 he became part of the Nobel Prize Committee on Physics, and the de facto head of the Nobel Prize Committee on Chemistry. Arrhenius basically awarded the 1903 Nobel Prize for Chemistry to himself! And he used (abused) his position to award Nobel Prizes to his friends (Jacobus van't Hoff, Wilhelm Ostwald, Theodore Richards) and to deny Nobel Prizes to his enemies (Paul Ehrlich, Walther Nernst). Both of the later did receive Nobel Prizes, but Paul Ehrlich never got a Nobel Prize in Chemistry, being granted a Nobel Prize for Medicine instead. Walther Nernst received a Nobel Prize in 1920 after Arrhenius blocked it for 20 years---his achievements in chemistry were so notable that the rest of the Nobel Committee revolted in 1920 to award him the prize. Arrhenius definitely had a vindictive side to him.

Svante Arrhenius part 1

By the end of the 19th century, the world had changed more since 1800 than in the thousand years before. From under 1 billion at the beginning of the century, the population was 1.5 billion and rising nearly 1% a year. Humankind was rumbling towards the population explosion of the 20th century. Advanced economies like the UK (35 million), Germany (60 million) and the USA (75 million) were industrialized and consuming hundreds of millions of coal per year. Railroads and coal burning ships had revolutionized transportation---the telegraph and telephone had revolutionized communications. Automobiles were just beginning to emerge, although not an environmental factor yet. Oil consumption was low, but about to explode. Humankind was on the threshold of being able to effect global environmental changes.

The dates of geological periods are always a bit arbitrary, except for the Cretaceous extinction--but sometime between 1800 and 2000 future scientists will say "Here marks the beginning of the Anthropocene period" and they will be right---although most were unaware of it at the time, and it is debated even now.

Svante August Arrhenius (1859-1927) was the first to realize that humankind could affect the global environment, and was in fact doing so. Although all the other figures I have discussed were important, it is with Arrhenius that the realization began that we are changing the global environment and the climate.

Arrhenius was a prodigy as a child, teaching himself to read at age 3 from the figures in his fathers' surveyor books and accounting figures. At age 8 he entered school at the fifth grade, and quickly became more adept at math than any of the other students in his school (which ran to high school) He sent for mathematical books from colleges and universities when his instructors were no longer able to teach him---and he was bored in high school. He wanted to attend the University of Uppsala early, but they would not admit him until he was 18--so in high school he studied his borrowed mathematics texts and waited.

In 1876 he entered the University of Uppsala and quickly became dissatisfied with the level of instruction he received--although he broadened his interests to chemistry. Due to rocky relationships with most of the faculty, whom he regarded as fools, he left the University of Uppsala in 1881 (without academic credit) after a serious dispute with Per Teodor Cleve, who found his chemistry work incomprehensible, to study at the Physical Institute of the Swedish Academy of Sciences in 1881. There Arrhenius researched under Erik Edlund about the electrical conductivity of electrolytes.

Michael Faraday had believed that salts dissolved into charged particles, which he called 'ions', a name we used for charged atoms and molecules today. This required an electric current--Faraday believed small electric currents were required to allow ionic chemical reactions to proceed. Arrhenius' insight was that ions could react with each other by themselves, without an intervening electrical current.

Arrhenius finished his doctoral thesis in 1884, a 150 page work (not exceptional for a doctoral thesis). What was exceptional was that his thesis contained 56 new ideas about physical chemistry--mostly to do with ionic chemical reactions. His thesis team was lead by Per Teodor Cleve, with whom Arrhenius had battled in the past--he came to the Physical Institute of the Swedish Academy of Sciences after Arrhenius did.

Arrhenius' thesis advisers thought his doctoral thesis mostly incomprehensible--giving it a rating in the 4th class. Upon Arrhenius' defense, they upgraded it to third class--barely acceptable. Arrhenius was incensed!

Arrhenius had his thesis translated into German (Germany being the center of physical chemistry and research in Europe) where it received wide admiration. Rudolf Clausius, Wilhelm Ostwald, and Jacobus Henricus van 't Hoff were very impressed. Ostwald even came to visit Arrhenius to persuade him to join his research team. Arrhenius wanted to very badly, but his father was very ill and in fact died later that year, so he declined.

Arrhenius's 1884 doctoral thesis won him the Nobel Prize for Chemistry in 1903.

After the heavyweights of the German chemists' establishment leaped so strongly to his defense, Arrhenius had a secure academic reputation--his old academic enemies could no longer hurt him. He became a traveling researcher for the Physical Institute of the Swedish Academy of Sciences, studying with Ostwald in Riga (then in Russia, now in Latvia), with Friedrich Kohlrausch in Würzburg, Germany, with Ludwig Boltzmann in Graz, Austria, and with van 't Hoff in Amsterdam.

In 1889, Arrhenius developed the concept of activation energy, the energy chemical reactions must absorb from their environment to proceed. Energy didn't come from nowhere, it must be present in the environment for chemical reactions to occur, and Arrhenius worked out how to determine what activation energies were needed for various chemical reactions to occur. This work resulted in the Arrhenius equation

In 1891 Arrhenius became lecturer in Physics at the Stockholm University College (now Stockholm University) and promoted to professor in 1895 (over much bitter opposition from his earlier academic battles). Arrhenius also had a bit of a personal scandal. In 1892 he began dating his student, Sofia Rudbeck--the old 'sex with the professor' thing. It was....unseemly. He married her in 1894, and it seems clear that the marriage was something he felt required to do to get the professorship. The marriage quickly curdled in a few months--she left him in 1895 right after he got the professorship. Arrhenius was devastated. And bored. He had worked hard to become a professor, but it was not what he wanted. Teaching second-rate minds in a second-rate college. Office hours. Grading papers. Quite a come-down after his achievements!

Arrhenius was bored. His reputation had gotten him a professorship, but it was not what he expected. He felt depressed, and trapped.

Arrhenius came across some works by Joseph Fourier, who had originated the idea that the atmosphere can cause a greenhouse effect. For the first time, infrared observations of the moon, by Frank Washington Very and Samuel Pierpont Langley beginning in 1890 had confirmed that the average temperature of the moon, day and night sides put together, was around 0 F. This confirmed that the calculations by Fourier and others were correct---without a greenhouse effect, the temperature of the Earth would be close to 0 F. And the only thing that could account for Earth's warmer temperature was the atmosphere. It had been known since Tyndall's time that carbon dioxide was a an infrared absorber.

Wait. Coal consumption was now a couple hundred million tons a year---carbon dioxide therefore was being emitted at almost a billion tons a year. Could humankind be changing the atmospheric composition and climate?

Arrhenius' head snapped up. It was a cloudy dull morning. February 21, 1895.

Friday, February 4, 2011

The discovery of Neptune

Or the story of nice guy John Couch Adams and nasty guys James Challis and George Biddell Airy.

William Hershel discovered Uranus in 1781, as noted in an earlier blog entry of mine. This discovery doubled the size of the solar system and made William Hershel the most famous astronomer of the age. But could there be more planets?

First, we need to go back to Isaac Newton and his discovery of how gravitation works. The gravitational attraction between two bodies depends on the mass of the two bodies multiplied by the square of the distance between the bodies. However, in the real universe there are uncounted numbers of bodies which each attract each other. Unfortunately, the attraction that three bodies in motion have on each other cannot be solved, even in principle. Let alone many more. The three body problem has still not been solved. However, we can reach a very good approximation by solving the gravitational attraction and motion of two massive bodies and then adding a third body (either less massive or further away) and then a fourth body, a fifth, and so on. The changes in velocity these further bodies have on the first bodies included in the equation are called perturbations.

For instance determining the orbital behavior of the moon around the earth, you first solve how the earth and moon attract each other, then put in the sun, Jupiter, Venus, Mars, Mercury, and Saturn. This was very complicated, and determining the moon's orbit drove Newton to distraction--Newton himself said that the problem of the moon's motion was the only one that ever made his head ache.

While a perfect solution to a many-body problem is impossible, by taking into account all the perturbations of the planets the error can be made vanishingly small. By the end of the 18th century the motion of the planets agreed with Newton's law perfectly as far as the telescopes of the time could determine.

Solving the problem of Uranus' orbital motion was relatively simple. You had to account for the sun, a small perturbation from Saturn, another small perturbation from Jupiter--and that was it. The inner planets (Mercury, Venus, Earth and Mars) were too small and too far away to have a measurable effect on Uranus's orbit.

But then came trouble.

In 1821 the French astronomer collected all the observational data or Uranus's orbit. He even went back through all the observations back to 1690 (Uranus had been first seen through a telescope and charted in 1690, but until Hershel it was just assumed to be a star. One astronomer charted Uranus 13 times in the middle 1700s, and assumed he had charted 13 stars!

The observations didn't fit. The distance observed between Uranus's theoretical position and its actual position was never more than 2 minutes of an arc. Or one-fifteenth of the apparent diameter of the full moon. Astronomers were dismayed. They didn't want a discrepancy of 2 arc-minutes. There shouldn't have been a discrepancy like that at all!

How to account for this? One idea was that Newton's inverse-square law of gravitation was wrong. Suppose instead of falling off to the second power (d2), it really fell off at an exponent of d2.001? Or d1.999? Then Newton's inverse-square law would seem to be correct until observing a really distant planet like Uranus before the discrepancy showed up.

The other possibility was that there was another planet out there, one that could account for Uranus's orbital behavior. Which was correct?

There was some thought that Newton might be slightly wrong--and there could be no surer way to scientific fame that to discover and correct a flaw in Newton's gravitational equations! But most scientists in general and astronomers in particular were against this idea. Newton's d2 formula was aesthetic. It was elegant. And most astronomers didn't want to mess with elegance.

Enter James Adams who graduated first in his class in mathematics from Cambridge in 1841. He decided to try and solve the problem of planet 8. The behavior of Uranus put some boundaries on the problem. If planet 8 was on the other side of the sun, it would be too far to perturb Uranus. So they had to be on the same side. Uranus had been ahead of it's predicted position through the late 1700s and into the early 1800s, but was now falling back closer to its predicted position. That meant that Uranus had overtaken Planet 8 sometime in the early 1800s and that Planet 8 was now behind Uranus (Uranus, closer to the sun would orbit faster. The actual overtaking was later determined to be in 1822).

The closer agreement between Uranus's actual position and its theoretical position during the 1800s also made some believe it was observational error that was being resolved as telescopes improved. However, that did not explain why the errors in Uranus's position were all on the same side.

Adams made some simplifying assumptions. Since Saturn is roughly twice the distance of Jupiter from the sun, and Uranus twice as far as Saturn is, Adams assumed that Planet 8 was twice as far from the sun as Uranus is. Adams also assumed that Planet 8's orbit was perfectly circular. Adams knew very well that all planetary orbits are ellipses, but most planetary orbits are close to circular, and calculating orbits was complicated enough on paper without trying all sorts of different elliptical configurations.

So Adams did simplify things, and some of his assumptions were off. One in particular turned out to be far off. Planet 8 is not twice the distance from the sun Uranus is, but only 1.5 times as far. But Adam's simplifications were reasonable ones.

By 1845 Adams had completed his calculations, and determined that on October 1, 1845, and for the rest of the decade, Planet 8 would be in the constellation Aquarius.

Adams gave his results to James Challis, the first villain of the story. James Challis was director of the Cambridge Observatory. Adams hoped that with the Cambridge Observatory at his disposal, Airy would make observations with dispatch. Adams was wrong. Airy, knowing that the observational search was likely to be tedious and most likely turn up nothing, ducked. He told Adams he was too busy, but he did fob Adams off with a letter of recommendation to the Royal Astronomer, George Burdell Airy.

Airy was a petty tyrant, always a nitpicker for detail and missing the big picture. Much later in life, he labored over expeditions sent around the world to measure the exact times the disc of Venus intersected the sun during transits in 1874 and 1882. By measuring from different vantage points on the Earth the exact times Venus's disk began and finished crossing the sun, the distance of Venus from Earth could be calculated precisely--and therefore all the distances of the planets from each other and the sun. Airy failed to account for Venus's atmosphere, which had been known about since the last pair of transits in the 1700s. The blurring effect of Venus's atmosphere ruined the the observations, and Airy's very expensive expeditions were failures.

The only success Airy had was a personal one. He developed eyeglass lenses that could correct astigmatism. He was himself astigmatic, literally and figuratively.

Airy, whose harsh treatment of his assistants and disdain for students was legendary, was the main Adams tried to contact. His letters to Airy went unanswered. In the days before the telephone, telegraph, and widespread railroads, Adams went down to Greenwich to visit Airy. Airy wasn't home. He went again. Airy wasn't home that time either. On a third visit, Adams was left to wait in the entryway for an hour before being informed that Airy was having dinner and would not be disturbed.

Adams left his paper with Airy who leafed through it and wasn't impressed. Airy was convinced that Newton's inverse-square law was in error and that he was going to find the error and correct Newton! Airy was convinced there was no new planet 8. Airy then wrote back to Adams sending him calculations using an adjustment of the inverse-square law, and nitpicking on two spelling mistakes Adams made in his paper.

Adams, realizing that he was dealing with a petty idiot, didn't bother to answer. He gave up.

Meanwhile, across the Channel, a young astronomer, Urbain Jean Joseph Leverrier was also working on the same problem. He made the same assumptions Adams did, and located Planet 8 in the same part of Aquarius Adams had done. Leverrier had done some astronomical work and made some contributions (as Adams had not--Adams was a mathematician) and Leverrier had the support of his superiors. Leverrier published his calculations with his superiors' support. Leverrier made his calculations 6 months after Adams.

Airy read the paper, and wrote Leverrier back with irrelevant nit-picking objections. Leverrier wrote back, and pointed out that Airy's objections were irrelevant.

Airy was reluctantly impressed. He did not write back that Adams had made the same calculations, and never wrote back Adams either telling him about Leverrier. He certainly did not recommend Adams' paper for publication.

Airy then wrote Challis and told him to start looking for Planet 8. This Challis did, but in a desultory way, not comparing stars positions from night to night. He didn't even start looking for three weeks after he got Airy's letter. As the weeks went by, Leverrier, hearing nothing back from Airy or Challis, lost patience. It had been 9 weeks since Airy had written Leverrier that he would be leading the effort to find Planet 8, and after so much time, it was obvious that the English were not putting any effort into the search.

The director of the Berlin Observatory received Leverrier's letter on September 18, 1846 and he was interested. He asked the lead astronomer, Gottfried Galle to take care of it.

The next few days had lots of clouds, while Galle prepared for the obsevations. It would have been tedious work, but then a graduate astronomy student, Heinrich Ludwig D'Arrest, reminded Galle that the Berlin Observatory had been preparing new star charts more accurate than any before, and to see if Aquarius had been charted. It had been, only 6 months before! A lucky break!

The night of September 23 was clear. The Aquarius star charts were in their hands. Galle and D'Arrest got to work, moving the telescope methodically across the constellation, calling out the stars and their positions one by one. Only 30 minutes later D'Arrest cried out "That's not on the chart!" It was the planet! And it was only about 1.4 times the diameter of the full moon away from the predicted position!

Naturally Galle and D'Arrest observed the planet for a week, enough to determine its slow motion and a small disc. On September 30, 1846, they announced their discovery.

Once the discovery was announced, Challis went back over his observations and discovered he had observed Planet 8 four times but had not bothered to compare positions and did not know what he had seen.

Both Airy and Challis had made fools of themselves, and they knew it. Neither mentioned Adams' paper.

John Hershel, an English astronomer,, the son of William Herschel who had discovered Uranus, had heard of Adam's work and made sure it was published--and tried very hard to get proper credit to Adams, and publicized the incompetence of Airy and Challis. Herschel had long disliked Airy, considering him a tyrant and unfit for the position of Royal Astronomer. Herschel had also heard of Airy's abusive practices towards Herschel's and others' students, but his attempt to get Airy dismissed went nowhere. Airy tried to blackball John Herschel from astronomy in Great Britain, but Herschel's well-deserved reputation (as well as his father's reputation for discovering Uranus and infrared rays) prevented this.

The whole thing became a huge row. The French were convinced that the English establishment was trying to steal credit for calculating Planet 8's existence and position. The English raged about the perfidious French. The French offered a sop---name Planet 8 'Leverrier' and change Uranus (Georgium Sidus) back to Herschel. No one really liked that idea, however. Several astronomers suggested that since Planet 8 was blue-green in color, it should be named Neptune, for the god of the sea--and this was adopted.

Leverrier and Adams met and became friends.

In 1860, Challis retired as director of the Cambridge Observatory, and nominated Adams for the post, in what seems to have been an apology. Challis was not really evil---just slipshod. Adams stayed there for 21 years, until he was offered the post of Royal Astronomer when Airy retired, having served for 45 years. However Adams by this point was 61, and had suffered some illnesses, and did not feel up to taking the position, and became a teaching professor at Cambridge. Adams chaired the International Meridian Conference in 1884, which set the Greenwich Observatory as the Earth's prime meridian for time. Adams and Airy both died in January 1892.

Gottfried Galle survived to July 1910, one month past his 98th birthday.

John Couch Adams

Urbain Jean Joseph Leverrier

It needs to be said that none of the people in this entry were the first to see Neptune. The first person to see it (and the first person to actually be first to see a new planet, since Uranus is visible to the naked eye) was Galileo--who observed it near Neptune December 27, 1612--more than 200 years before its discovery!

In this drawing, Neptune is the 'star' in the green box with the notation 'fixa' or fixed--as in a fixed star. Here is the image from Galileo's notebooks:

Galileo's notebook from January 27, 1613

Interestingly in July 2009, David Jameson, a physicist from Melbourne Australia, discovered that Galileo used a different type of ink to mark Neptune's location in the January 1613 observation--one different from the rest of the page. Neptune was just turning retrograde in December 1612, its motion was not apparent. But it was moving more quickly against the fixed stars by late January 1613. Was Galileo aware that he had discovered a new planet? His notes don't say. But it is interesting that he used a different ink to mark Neptune, and that he did not label it a fixed star.

Perhaps he thought that the discoveries he had publicized were disturbing enough to the church--another planet that could not be seen with the naked eye would be just too much. So he kept the knowledge to himself--knowing the world was not yet ready for it. I'd like to think that was so.