Global Warming Science In The Age Of Washington And Jefferson: William Charles Wells
Thermodynamics has been a hot topic lately, some places on the Web.
Oops, did I say that with a straight face? It may be a bad pun, but it’s true. I’m speaking in particular of the Second Law, popularly rephrased in song by the British comic duo, Flanders and Swann:
"Heat won’t pass from a cooler to a hotter; you can try it if you like, but you’d far better notter."
Or, to quote it more formally, as it was stated in 1851 by Rudolf Clausius, one of the central founders of the discipline of Thermodynamics:
"No process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature."
Some have been arguing that this means that the “Greenhouse Effect” is impossible, since (supposedly) it asserts that the Earth’s surface is warmed by the radiation from layers of the atmosphere colder than the surface itself—and that, goes the argument, would be heat passing “from a cooler to a hotter.”
Unfortunately perhaps, this argument is not correct. To see why not, we’ll take a look at the life and career of a fascinating, yet little-remembered Scots-English physician named William Charles Wells.
Let’s begin by considering the context into which Wells was born in 1757.
Modern chemistry did not yet exist. Robert Boyle (1627-1691) had done good work in separating the then-proto-discipline from its roots in alchemy, but “the father of modern chemistry,” Antoine Lavoisier, was a mere fourteen years old. The old theory of “phlogiston”—propounded by J. J. Becher (1635-1682) and associated with Boyle—remained dominant, and would not be entirely dead until the passing of the eminent Joseph Priestly in 1804.
Sir Isaac Newton’s physics had triumphed, but still troubled some. For instance, poet and visionary William Blake—born like Wells in 1757—would wrestle with Newton’s ideas in lines like these:
. . . and Newton’s particles of light
Are sands upon the Red Sea shore,
Where Israel’s tents do shine so bright.
The political climate was dominated by conflict between England and France. In 1757, they were the world’s leading colonial powers, and their rivalry was playing out in military conflict on a near-global scale: Sir Robert Clive was conquering India for the British Crown; England’s leading ally, Frederick the Great, was fighting for Prussia’s political life against the Austrians, Russians and French (and occasionally taking time to dash off yet another flute sonata.) And in the American colonies, a young George Washington, then a colonel commanding the Virginia Regiment, was conducting a grinding defense of the frontier against French-allied Indian raiders.
Well's Life, Part One
In South Carolina things were quieter, for the moment. The Colonial capital, Charleston—“Charlestown,” as it was then written—was peaceful on May 24, as Mary Wells gave birth to her fourth child, William Charles Wells. Mary had emigrated from Dumfries, Scotland in 1753 with her husband Robert, a merchant, printer and bookseller. He would be described as “possessed of more than common talents and attainments;” she would be praised as “generous and high-minded.”
The young William Charles must have shown academic promise as he grew up; before his eleventh birthday, he was sent to school back in Dumfries. Completing his studies there in 1770, he then attended “several of the lower classes” at the University of Edinburgh. Apprenticeship to a Dr. Alexander Garden, a Charleston physician and naturalist, followed. Wells later said that he had learned more during this time than during any other period of his life—albeit not due so much to his master’s instruction, as to his own sheer hard study. That study would lead him down a winding road indeed. At the end of it lay a remarkable paper entitled simply “On Dew.”
"On Dew," Part One
It’s not altogether clear why the topic of dew came to occupy Wells’ attention so completely. But between 1811 and 1814, he devoted countless hours to detailed physical investigation of nearly all things dewy. He measured the deposition of dew by weighing wool discs which absorbed it. He measured surface and air temperatures in a multitude of different conditions: clear weather and cloudy; with covered thermometers and exposed ones; metal objects, wooden objects, cloths, gravel and grass. Always, he meticulously noted everything. Frequently, he worked the night through, trudging back at daybreak to care for his medical patients. And above all else, he thought long and carefully.
At the end of his labors, he had an essay that would win both praise and widespread acceptance—not to mention the Royal Society’s 5th Rumford Medal.
The essay is the length of a short book, and is in three parts. Part One, “Of the Phenomena of Dew,” briefly reviews existing literature. Wells then describes some of the experiments made, and how they lead to three main conclusions:
1) Exposure to sky increases production of dew;
2) Difference in the mechanical state of bodies affects the quantity of dew deposited upon them. For example, “. . . more dew is formed upon fine shavings of wood than upon a thick piece of the same substance.”
3) “Bright metals. . . attract dew much less powerfully than other bodies. . .”
Having considered these “circumstances” affecting the formation of dew, Wells examines the “circumstances” affecting the cold which is dew’s precursor: on clear, still nights, the grass would become much cooler than the air temperature (customarily measured at 4 feet); long grass would cool more than short grass; and wind or cloud tended to eliminate this difference in temperature—although high cloud “would yet frequently allow of the grass being several degrees colder than the air.” The ground beneath the grass would be warmer; metal lying upon the grass tended to be warmer, too.
These “circumstances” all have one common thread: the concept of thermal radiation. Exposure to the cold night-time sky meant a minimum of warming radiation reaching an object, even as it radiated away its own heat; “fine shavings” can radiate heat better than can a “thick piece” of wood; and “bright metals” were (and are) known to be relatively poor radiators.
Life, Part Two
But it wasn’t radiation that had occupied Wells’ thoughts back in 1775; it was politics. The American Revolution was brewing in Charleston as elsewhere, and the Wells family held firmly to their loyalty to the British Crown. William received a demand to sign a pledge of loyalty to the Patriot cause.
Unwilling to do so, he returned to the University of Edinburgh, and then pursued further medical study in London. In 1779 he set his studies aside to take work as surgeon to a Scottish regiment in Holland. He soon resigned, dissatisfied with the regimental commander, whom he actually challenged to a duel! (The commander jailed him instead of accepting.)
Freed, Wells returned to study, this time at the University in Leyden. In due course he completed a dissertation, significantly entitled On Cold. It was his final requirement for the degree of Doctor of Medicine, which he received from the University of Edinburgh in 1780.
There followed a period replete with colorful adventures—tempting to relate in detail, but less than relevant to our purpose here. Briefly, Wells returned to America, shuttling back and forth between Charleston and Saint Augustine, Florida, according to the political ebb and flow. In Charleston he was:
. . . at the same time an officer in a corps of volunteers; a printer, a bookseller, and a merchant, a trustee for some of his father’s friends in England for the management of affairs of considerable importance in Carolina; and on one occasion. . . Judge Advocate.
(He won the case.)
In St. Augustine, he edited the first newspaper published in Florida—having had to rebuild the press himself—and served again as captain of a corps of volunteers, as well as manager and sometime actor in a theatrical venture raising funds for impoverished Loyalist refugees:
He had great success [as] Lusignan in Zara, and [as] Old Norval in Douglas; but did not succeed [as] Castalio in The Orphan, and failed, as might be expected by those who knew him, in Comedy.
This period was capped by false imprisonment for debt in Charleston, and shipwreck on the return voyage to St. Augustine—Wells saved himself by swimming ashore, naked, in the middle of the night.
"On Dew," Part Two
Part Two, “On The Theory Of The Dew,” presents Wells’ theory. He begins by reviewing previous theories. Notably, Aristotle had written that dew was similar to an “invisible rain”—it was moisture that fell, somehow invisibly, from the sky. This view was still held in Well’s day. But there had been a more recent theory that dew was an “electrical phenomenon,” since metals, known to be excellent conductors of electricity, were also known to be poor at attracting dew; however, this idea had not proven very workable.
Still other writers had simply noted an association between dew and cold, considering that dew produced cold. Wells had the insight to reverse the causality: dew, he said, is the product of cold—and he produced experimental observations to prove it, giving detailed accounts of his temperature measurements in various controlled circumstances.
He added that the quantity of dew formed depends upon both temperature and humidity—“the existing state of the air in regard to moisture.” Moreover, “The formation of dew, indeed, not only does not produce cold, but like every other precipitation of water from the atmosphere, produces heat.”
After adding some less central “circumstances,” Wells finally states the core of his theory:
. . . dew appears in an open and level grass field during a still and serene night. The upper parts of the grass radiate their heat into regions of empty space, which consequently send back no heat in return; its lower parts, from the smallness of their conducting power, transmit little of the earth’s heat to the upper parts, which, at the same time, receiving only a small quantity from the atmosphere, and none from any other lateral body, must remain colder than the air, and condense into dew its watery vapour, if this be sufficiently abundant. . .
Wells then discusses an aspect of what we would now call “thermodynamics.” Count Rumford (who had in 1798 challenged Lavoisier’s theory that heat was a “subtle fluid” called “caloric” by showing that this fluid was not conserved during prolonged heating by friction) believed that cold was more than the mere absence of heat—that cold could radiate by "frigorific rays." Wells refers to one support for this belief, an “experiment which has been used to prove the reflection of cold”:
. . .the bulb of a thermometer [is] placed before a larger cold body. . . In this situation the small body radiates heat to the larger, without receiving an equivalent from it, and, in consequence, becomes colder than the air through which its heat is sent, notwithstanding that it is continually gaining some heat, both from the air which surrounds it and from the walls and contents of the apartment in which the experiment is made.
Note that Wells, in describing this experiment, which may have been performed in 1665 or even earlier, does not follow Rumford's concept. Rather, he explains the effect in essentially modern terms: radiation passes between two bodies at unequal temperatures, producing a net flow from warmer to cooler.
Wells identifies the same dynamic at work in interchanges between atmosphere and the surface of the Earth:
Radiation of heat by the earth to the heavens must exist at all times; but, if the sun be at some height above the horizon. . . the heat emitted by it to the earth will overbalance, even in places shaded from its direct beams, that which the earth radiates upwards.
This statement is supported by accounts of daytime observations Wells made during cloudy and foggy conditions.
In a calm and serene night, however, when consequently little impediment exists to the escape by radiation of the earth’s heat to the heavens, and when no heat can be radiated by the sun to the place of observation, an immense degree of cold would occur on the ground, if the following circumstances did not combine to lessen it. 1. The incapacity of all bodies to prevent entirely the passing of heat by conduction from the earth to substances placed upon them. 2. The heat radiated to these substances by lateral objects. 3. The heat communicated to the same substances by the air. 4. The heat which is evolved during the condensation of the watery vapour of the atmosphere into dew.
Note that in essence, Wells is outlining a surface heat budget—a more-or-less comprehensive accounting of the energy flowing to and from the earth’s surface. This, too, would be a vexed matter in the ‘global warming debate’ of the early 21st century.
Wells continues by considering the most obvious atmospheric “impediment,” clouds:
No direct experiments can be made to ascertain the manner in which clouds prevent or occasion to be small the appearance of a cold at night upon the surface of the earth greater than that of the atmosphere; but it may, I think, be firmly concluded, from what has been said in the preceding article, that they produce this effect, almost entirely by radiating heat to the earth in return for that which they intercept in its progress from the earth towards the heavens. . .
Wells then shows that he was aware of what we now term the “lapse rate”—the normal decline of temperature as one ascends higher in the atmosphere. (By 1811, the year Wells began his researches on dew in earnest, a number of balloon flights had been made in part to measure temperature and humidity.) More, he draws an important consequence:
Dense clouds near the earth must possess the same heat as the lower atmosphere, and will therefore send to the earth, as much, or nearly as much heat as they receive from it by radiation. But similarly dense clouds, if very high, though they equally intercept the communication of the earth with the sky, yet being, from their elevated situation, colder than the earth, will radiate to it less heat than they receive from it, and may, consequently, admit of bodies on its surface becoming several degrees colder than the air.
This, though Wells certainly could not have dreamed it, is actually an important part of the mechanism of the greenhouse effect: when greenhouse gases increase, they shorten the average length that radiant heat can travel through the atmosphere before being absorbed. Therefore, the average altitude from which heat can radiate to space increases. But since higher altitudes imply colder air, and since colder air is a less effective radiator, heat loss to space is slowed.
Wells then comments on the effects of cloudiness in producing maritime climates, and on the advection of fresh parcels as it affects dew production, temperature and the phenomenon of “frost hollows”:
There is a remark by Theophrastus, which has been confirmed by other writers, that the hurtful effects of cold occur chiefly in hollow places. . .
This leads to a very interesting discussion which reveals that some of the balloon flights mentioned above had observed not only normal lapse rates, but also what we now call “temperature inversions.” Wells begins by arguing that:
. . . air is capable, both of absorbing heat which is radiated into it, and of radiating heat which had before formed a part of its temperature. . .
Let it be supposed then, that while the earth in this [warmed] state, radiates upwards a quantity of heat, a foot in depth of the incumbent air is capable of stopping a 1000th of what it hence receives, and of converting it into heat of temperature. The consequence must be that the next foot, from receiving only 999 parts of what had been emitted by the earth, will not be so much heated as the first foot, though it should absorb the same proportional quantity of what enters it. In this way every successive foot will acquire a less quantity of heat than the preceding. . .
[Therefore] the heat of the air in a clear and calm night ought to increase [editorial emphasis]. . . in some decreasing geometrical ratio as the atmosphere ascends. . .
Well's formulation is a little obscure here, but compare a popular modern source, Wikipedia:
An inversion is also produced whenever radiation from the surface of the earth exceeds the amount of radiation received from the sun, which commonly occurs at night . . .
Wells applies this principle to the situation of a hill with an adjacent plain, concluding that temperature differentials of 10 degrees (F) are quite plausible. Moreover, the effects of differential wind speeds upon the heights and the plain will tend to amplify this radiationally produced effect. Continuing, Wells observes that:
An explanation may be now easily given of an observation by Mr. Jefferson, of Virginia, which, however, had also been made by Aristotle and Plutarch, that dew is much less copious on hills than it is upon plains. . . as the production of dew must be in proportion to the whole depression of the temperature of the air which furnishes it. . . it may readily be inferred that dew shall sometimes be altogether wanting on a hill, though abundant on a plain at its foot, agreeably to what has been actually observed by Mr. Jefferson.
American readers may take a moment to bask in the Presidential scientific citation! One wonders what, if anything, Wells felt about thus citing one of the Patriots whose victory had exiled him from his birthplace.
More miscellaneous points having to do with radiative cooling and dew at different altitudes and involving different substances and colors follow, before Part Two concludes with a lengthy discussion of the theory that dew actually rises from the earth and from vegetation. This idea goes back to Descartes, but really came into the literature with an author named Gersten in 1733.
It was a theory associated with the French Academy, and it may be connected with a fanciful elaboration found in Edmund Rostand’s 1897 play, Cyrano de Bergerac. Rostand, it turns out, was cribbing from the historical Cyrano’s 1656 satire, A Voyage to the Moon. Here is the relevant passage, in the 1687 English translation:
I planted my self in the middle of a great many Glasses full of Dew, tied fast about me; upon which the Sun so violently darted his Rays, that the Heat, which attracted them, as it does the thickest clouds, carried me up so high, that at length I found my self above the middle Region of the Air.
Cyrano, an admirer of Descartes, evidently fastened upon the disappearance of the dew in the morning sun, rather than upon its deposition as in Wells or Descartes. Envisioning the disappearance as caused by a Solar attraction, it was a natural imaginative step to apply this supposed attraction as a lifting agent! Of course, the context in which Cyrano was writing is clearly fantastic, and offers no reliable guide to what he actually considered practical.
At any rate, Wells admits Descarte’s suggestion that moisture can rise from soil or vegetation is a possibility, but argues convincingly that any such effect must be very small indeed.
Life, Part Three
Wells’ real-life adventures to this point had been almost reminiscent of Cyrano’s. But now his life would take a turn into calmer waters. In 1784 he returned to England and settled in London; further wanderings were limited to a three-month trip to Paris in the spring of 1785. Once settled, Wells set out to establish his own practice, and to write a modest but steady stream of scholarly papers, mostly upon medical topics. Although the growth of his practice was slow at first, he gradually established a secure, if modest, professional status.
In his scholarly work he showed himself to be an acute observer and a careful and incisive analyst. These qualities have been noted repeatedly since his day. For example, it has been pointed out that his work in nephrology wholly anticipated the work of Dr. Bright, and that his studies in optical physiology involved him in controversy with no less an opponent than the then-famous Erasmus Darwin. But It was the latter’s more famous grandson, Charles Darwin, who would later write that Wells “distinctly recognizes the principle of natural selection, and this is the first recognition which has been indicated. . .”
Yet on the whole Wells remained something of an “outsider” in his own time, and his scholarly work was not very influential, despite its good quality. The main exception to this scholarly obscurity was On Dew.
"On Dew," Part Three
Part Three deals in turn with applications—or near-applications—of radiational cooling.
First is the “near-application”: Wells explains how “inside shutters” influenced the formation of condensation upon the inside surfaces of windows in winter. Windows so covered were more heavily bedewed, because they were colder than unshuttered ones. That is logical since the shutters, of course, shielded the glass from the heat radiated from the room’s interior.
He also notes that the moisture deposited was less than that which a similar temperature differential would have produced in his experiments outdoors. He ascribes this to an (inferred) lower relative humidity inside:
The air of the chamber had once been a portion of the external atmosphere, and had afterwards been heated, when it could receive little accession to its original moisture. It consequently required being cooled considerably, before it was even brought back to its former nearness to repletion with water; whereas the whole external air is commonly, at night, nearly replete with moisture, and therefore readily precipitates dew on bodies only a little colder than itself.
The experience of the age of central heating suggests that he was entirely correct—it’s common to include humidifiers in cold-climate heating systems, precisely to avoid overly dry inside air due to the effect Wells describes.
Next he discusses the custom of sleeping on the roofs of houses, which was, and is, observed in certain tropical countries. This custom had been noted by Count Rumford, who:
. . . rightly conjectured that the inhabitants. . . are cooled during this exposure by the radiation of their heat to the sky; or, according to his manner of expression, by receiving frigorific rays from the heavens.
Wells, reverting to a physician for the moment, further speculates that the supposed “hurtful effects of the night air”—ascribed by Descartes to “certain noxious vapours. . . exhaled from the earth,” and by Descartes’ contemporaries to the dew itself—may be due to simple radiational chilling.
Thirdly, Wells turns to the subject of protecting plants from cold—beginning by laughing at himself:
I had often, in the pride of half knowledge, smiled at the means frequently employed by gardeners to protect tender plants from cold, as it appeared to me impossible that a thin mat, or an such flimsy substance, could prevent them from attaining the temperature of the atmosphere, by which alone I thought them liable to be injured. But, when I had learned that bodies on the surface of the earth become, during a still and serene night, colder than the atmosphere, by radiating their heat to the heavens, I perceived immediately a just reason for the practice, which I had before deemed useless.
He followed up this insight by experimenting with fine fabric shields above grass, finding that the sheltered grass (though sometimes as much as 3o F cooler than the air) was consistently much warmer than unsheltered grass nearby—as much as 11 o F, on one occasion.
Wells’ fourth point is that in line with gardener’s practical wisdom, snow (when present) must act analogously to other substances which protect plants by blocking radiational cooling.
He then examines the idea that moonlight exerted a putrefying influence upon “animal substances.” As he saw it, this belief existed in his day mostly in African and Caribbean folklore, although such ancient authors as Pliny and Plutarch had also affirmed it.
Warning that “The bare mention of the subject. . . will be apt to excite ridicule,” Wells went on to suggest that the belief may in fact have a kernel of truth: dew is apt to accompany moonlight, since both are associated with clear nights. Therefore it is possible that any “animal substances” which are allowed to become thoroughly bedewed will indeed be prone to spoil—but the real cause is the moisture upon their surfaces, not their exposure to moonlight.
The final (and most extended) discussion of an application of radiational cooling is an exotic one; it seems that Bengalis had learned how to manufacture ice in their warm climate by using radiational cooling. Two authors, Sir Robert Barker and a certain Mr. Williams, had published accounts of the practice.
According to their descriptions, shallow pits were dug in open ground, and the bottoms of these pits were insulated with dry straw. Shallow unglazed earthenware pans, filled with boiled water, were exposed to the night sky on cold (but, in Bengal, not sub-freezing) nights. Radiational cooling would cause the water to freeze. The resulting discs of ice were slipped out of the pans, and could presumably be sold or stored for later use.
Both authors and a commentator, the great Sir Humphrey Davy, believed that evaporative cooling played a great part in the cooling of the water; but Wells ascribed the effect entirely to radiation. He argues his case skillfully and convincingly, considering quite minutely all the circumstances Barker and Williams mention; but he does not neglect to experiment himself.
First, he describes his investigation to quantify evaporative cooling as temperatures approach the freezing point:
While attending to this subject, I became desirous of acquiring some knowledge of the degree of cold which might be produced by evaporation from water contained in a shallow vessel. With this view I placed on a featherbed, situated between the door and window of a room in my house in London, two china plate, into one of which as much water was poured, as covered its bottom to the depth of a quarter of an inch. The other plate was kept dry. The bulb of a small thermometer being then applied to the inside of the bottom of each plate, I observed upon many days, in various seasons of the year, the difference between these instruments while the door and window were open. I found, in consequence, that when the temperature of the air in the room was 75o. . . the thermometer in the plate containing water, was between 6 and 7 degrees lower than the one in the dry plate; that the difference between these thermometers diminished gradually as the air became colder; and that when the temperature of the air was 40o, the lowest for which I have any observation, the difference was only 1o1/2. At 32o, therefore, it would have been very small. . .
Moreover, when he successfully replicates the processes as described by each of his sources he finds no difficulty in making ice in glazed vessels. Since they are impermeable, once the first film of ice has formed upon the surface of the water no further evaporation should take place. Yet the freezing continued to completion in these vessels, as in all others.
This discussion essentially brings On Dew to an end. What can we take from Wells’ essay today?
Of course Wells attained his main objective: he correctly deduced the principal mechanisms producing the mundane—yet in Wells’ day still deeply mysterious—phenomenon of dew. Further, he elaborated upon many different ‘circumstances connected’ with the phenomenon. But his work also fed into a wider web of scientific observation and analysis that would influence thinkers such as Rudolf Clausius, who was mentioned at the outset of this Hub. Clausius may or may not have been specifically aware of Wells’ work in 1850 when he formulated his statements of the Laws of Thermodynamics; but he was well aware that radiation can and does pass between objects at different temperatures.
This topic had been a very active subject of research around the turn of the eighteenth century; in addition to the American-born Count Rumford, mentioned earlier, three Swiss researchers, must be noted: Horace de Saussure, his student Marc-August Pictet, and their friend and colleague at the Academy of Geneva, Pierre Prévost.
(It’s worth noting in passing that both Rumford and Pictet spent time in London, where the latter’s book on heat was published in 1791, in an English translation entitled An Essay On Fire. Pictet also edited a journal dedicated to reporting on British science, and additionally was well-known to Joseph Fourier—credited with the first paper on the ‘greenhouse effect’ in 1824. Rumford endowed the prize named after him, which Wells would later win.)
These researchers were concerned with the question of the nature of heat. Some, like Rumford, believed it to be essentially a vibration of some kind; others, like Pictet and particularly Prévost, thought it was a substance, invisibly emitted by hot objects. They carried out many experiments to try to clarify this question; among them was “Pictet’s Experiment”—that is, the “experiment which has been used to prove the reflection of cold,” mentioned by Wells, and described above.
The modern view advanced by Wells—that there occurs a mutual flow of heat between objects at different temperatures—was the view advanced by Prévost. (Possibly Wells been exposed to this view via Pictet’s discussion of it in An Essay On Fire.) What Clausius would later demonstrate (among other things) was that the net flow would necessarily be from warmer to cooler.
Wells accomplishment was to show that such radiational exchanges occur between ground and atmosphere, and can be observed and measured. As it turned out, Wells’ measurements would be the first of a lengthy campaign, one extending to the present day. (This story is outlined in my “Fire From Heaven” Hubs.)
What Wells accomplished, armed only with insight, persistence and a collection of thermometers, paper, string, boards, and metal plates, is a powerful reminder that the roots of climate science are not merely theoretical and analytical. From the very beginning, there has been careful, painstaking observation.
Perhaps the most eloquent of all appreciations of On Dew is this description, written fifty years after the publication of Wells’ masterwork. The author was the 23rd Rumford Medal winner, and the discoverer of the phenomenon of ‘greenhouse gases,’ physicist John Tyndall:
With broken health Wells pursued and completed this beautiful investigation; and, on the brink of the grave, he composed his Essay. It is a model of wise enquiry and of lucid exposition. He made no haste, but he took no rest till he had mastered his subject, looking steadfastly into it until it became transparent to his gaze. Thus he solved his problem, and stated its solution in a fashion which renders his work imperishable.
Since his time various experimenters have occupied themselves with the question of nocturnal radiation; but, though valuable facts have been accumulated, if we except a supplement contributed by Melloni, nothing of importance has been added to the theory of Wells.
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