GAUSS’S DAY of RECKONING A Famous STORY about the boy wonder of mathematics has taken on a life of its own. L ET ME TELL YOU A STORY, ALTHOUGH IT’S SUCH A VERY WELL-WORN NUGGET OF MATHEMATICAL LORE THAT YOU’VE PROBABLY ALREADY HEARD IT.------- IF NOT --- HERE GOES. In the 1780s a provincial German schoolmaster gave his class the tedious assignment of summing the first 100 integers. The teacher’s aim .was to keep the kids quiet for half an hour, but one young pupil almost immediately produced an answer: 1+2+3+...+98+99+100 = 5,050. The smart aleck was Carl Friedrich Gauss, who would go on to join the short list of candidates for greatest mathe-matician ever. Gauss was not a calculating. prodigy who added up all those numbers in his head. He had a deeper insight: If you “fold” the series of numbers in the middle. and add. them. in pairs—1+ 100, 2+99, 3+98, and so on—all the pairs sum to 101. There are 50 such pairs, and so the grand total is simply 50x 101. The more general formula, for a list of consecutive numbers from 1 through n, is n(n+1)/2. The paragraph above is my own rendition of this anecdote, written a few months ago for another project. I say it’s my own, and yet I make no claim of originality. The same tale has been told in much the same way by hundreds of others before me. I’ve been hearing about Gauss’s schoolboy triumph since I was a schoolboy myself. The story was familiar but until I wrote it out in my own words , I had never thought carefully about the events in that long-ago classroom. Now doubts and questions began to nag at me. For example: How did the teacher verify that Gauss’s answer was correct? If the schoolmaster already knew the formula for summing an arithmetic series, that would somewhat diminish the drama of the moment. If the teacher didn’t know, wouldn’t he he spending his interlude of peace and quiet doing the same mindless exercise as his pupils? There are other ways to answer this question, but there are other questions too, and soon I was wondering about the provenance and authenticity of the whole story. Where did it come from, and how was it handed down to us? Do scholars take this anecdote seriously as an event in the life of the mathematician? Or does it belong to the same genre as those stories about ewton and the apple or Archimedes in the bathtub, where literal truth is not the main issue? If we treat the episode as a myth or fable, then what is the moral of the story? To satisfy my curiosity I began searching libraries and online resources for versions of the Gauss anecdote. By now I have over a hundred exemplars, in eight languages. The sources range from scholarly histories and biographies to textbooks and encyclopedias, and on through children’s literature, Web sites, lesson plans, student papers, Usenet newsgroup postings and even a novel. All of the retellings describe what is recognizably the same incident—indeed, I believe they all derive ultimately from a single source— and yet they also exhibit marvelous diversity and creativity, as authors have struggled to fill in gaps, explain motivations and even construct a coherent narrative. (I soon realized that I had done a bit of ad lib type embroidery myself.) After reading all those variations on the story, I still can’t answer the fundamental factual question, “Did it really happen that way?” I have nothing new to add to our knowledge of Gauss. But I think I have learned something about the evolut-ion and transmission of such stories, and about their place in the culture of science and mathematics. Finally, I also have some thoughts about how the rest of the kids in the class might have approached their task. This is a subject that’s not much discussed in the literature, but for those of us whose talents fall short of Gaussian genius, it just may be the most pertinent issue. WUNDERKIND I started my survey with five modern biographies of Gauss: books by G. Waldo Dunnington (1955), Tord Hall (1970), Karin Reich (1977), W. K. Buhler (1981) and a just-issued biography by M. B. W. Tent (2006). The schoolroom incident is related by all of these authors except Bubler. The versions differ in a few details, such as Gauss’s age, but they agree on the major points. They all mention the summation of the same series, namely the integers from 1 to 100, and they all describe Gauss’s method in terms of forming pairs that sum to 101. None of these writers express much skepticism about the anecdote (unless Buhler’s silence can be interpreted as doubt). There is no extended discussion of the story’s origin or the evidence supporting it. On the other hand, references in some of the biographies did lead me to the key document on which all subsequent accounts seem to depend. This In the portrait Sartorius gives us, Gauss was a wunderkind. He taught himself to read, and by age three he was correcting an error in his father’s arithmetic. Here is the passage where Sartorius describes Gauss’s early schooling in the town of Braun-schweig, near Hanover . The translation, except for two phrases in brackets, is by Helen Worthington Gauss, a great-grand-daughter of the mathematician. In 1784 after his seventh birthday the little fellow entered the public school where elementary subjects were taught and which was then under a man named Büttner. It was a drab, low school-room with a worn, uneven floor.... Here among some hundred pupils Büttner went back and forth, in his hand the switch which was then accepted by everyone as the final argu- ment of the teacher. As occasion warranted he used it. In this school—which seems to have followed very much the pattern of the Middle Ages—the young Gauss remained two years without special incident. By that time he had reached the arithmetic class in which most boys remained up to their fifteenth year. Here occurred an incident which he often related in old age with amusement and relish . In this class the pupil who first finished his example in arithmetic was to place his slate in the middle of a large table. On top of this the second placed his slate and so on. The young Gauss had just entered the class when Büttner gave out for a problem [the summing of an arithmetic series]. The problem was barely stated before Gauss threw his slate on the table with the words (in the low Braunschweig dialect): “There it lies.” While the other pupils contin- ued ~counting, multiplying and adding], Büttner, with conscious dignity, walked back and forth, occasionally throwing an ironical, pitying glance toward this the youngest of the pupils. The boy sat quietly with his task ended, as fully aware as he always was on finishing a task that the problem had been correctly solved and that there could be no other result. At the end of the hour the slates were turned bottom up. That of the young Gauss with one solitary figure lay on top. When Büttner read out the answer, to the surprise of all present that of young Gauss was found to be correct, whereas many of the others were wrong. Incidental details from this account reappear over and over in later tellings of the story. The ritual of piling up the slates is one such feature . (It must have been quite a teetering heap by the time the hundredth slate was added!) Büttner’s switch (or cane, or whip) also made frequent appearances until the 1970s but is less common now; we have grown squeamish about mentioning such barbarities. What’s most remarkable about the Sartorius telling of the story is not what’s there but what’s absent. There is no mention of the numbers from 1 to 100, or any other specific arithmetic progression. And there is no hint of the trick or technique that Gauss invented to solve the problem; the idea of combining the numbers in pairs is not even discussed, nor is the formula for summing a series . Perhaps Sartorius thought the procedure was so obvious it needed no explanation. A word about the bracketed phrases: Strange to report, the Worthington Gauss
translation does mention the first 100 integers. Where Sartorius writes simply
MAKING HISTORY If Sartorius did not specify a series running from 1 to 100, where did those numbers come from? Could there be some other document from Gauss’s era that supplies the missing details? Perhaps someone to whom Gauss told the story “with amusement and relish” left a record of the occasion. The existence of such a corroborating document can not be ruled out, but at present there is no evidence for it. None of the works I have seen makes any allusion to any other early source. If an account from Gauss’s lifetime exists, it remains so obscure that it can’t have had much influence on other tellers of the tale. In the literature I have surveyed, the 1-100 series makes its first appearance in 1938, some 80 years after Sartorius wrote his memoir . The 1-100 example is introduced in a biography of Gauss by Ludwig Bieberbach (a mathematician notorious as the principal instru ment of Nazi anti-Semitism in the German mathematical community). Bieberbach’s telling of the story is also the earliest I have seen to specify Gauss’s strategy for calculating the sum—the method of forming pairs that add to 101. Should Bieberbach therefore be regarded as the source from whom scores of later authors have borrowed these “facts”? Or is this a case of multiple independent invention? If you think it utterly implausible that two or more authors would come up with the same example and the same method, then Bieberbach himself is disqualified as the source. A full millennium before Gauss and Büttner had their classroom confrontation, essentially the same problem and solution appeared in an eighth-century manuscript attributed to Alcuin of York. Furthermore, in the years since Bieberbach wrote, there is unmistakable evidence of independent invention. Not all versions agree that the sequence of numbers was the set of consecutive integers from 1 through 100. Although that series is the over-whelming favorite, many others have been proposed. Some are slight variations: 0-100 or 1-99. Several authors seem to feel that adding up 100 numbers is too big a job for primary-school students, and so they trim the scope of the assignment, suggesting 1-80, or 1-50, or 1-40, or 1-20, or 1-10. A few others apparently think that 1-100 is too easy, and so they give 1-1,000 or else a series in which the difference between successive terms is a constant other than 1, such as the sequence 3, 7, 11, 15, 19, 23, 27. Perhaps the most influential version of the story after that of Sartorius is the one
told by Eric Temple Bell in THE NARRATIVE URGE It’s a challenge to sort out patterns of influence and transmission in such a collect- ion of stories. When a later author mentions the series 81297 + 81495 + we can be pretty sure those numbers came from Bell. When the example given is 1-100, however, it’s not so easy to trace the line of inheritance—if there is one. And the dozen or so other sequences that appear in the literature argue for a high rate of mutation; every one of those examples had to be invented at least once. Tellers of a tale like this one seem to work under a special dispensation from the usual rules of history-writing. Authors who would not dare to alter a fact such as Gauss’s place of birth or details of his mathematical proofs don’t hesitate to then embellish this anecdote, just to make it a better story. They pick and choose from the materials available to them, taking what they need and leaving the rest—and if nothing at hand suits the purpose, then they invent! For example, several authors show a familiarity with Bell’s version of the story, quoting or borrowing distinctive phrases from it, but they decline to go along with Bell’s choice of a series beginning 81297, falling back instead on the old reliable 1-100 or inserting something else entirely. Thus it appears that what is driving the evolution of this story is not just the accumulation of errors of transmission, as in the children’s game “whisper down the lane”; authors are deliberately choosing to “improve” the story, to make it a better narrative. For the most part, I would not criticize this practice. Effective storytelling is surely a legitimate goal, and outside of formal scholarly works, a bit of embroidery on the bare fabric of the plot does no harm . A case in point is the theme of “busywork” found in most recent tellings of the story (including mine) . It seems we feel a need to explain why Büttner would give his pupils such a long and dreary exercise. But Sartorius says nothing at all about Büttner’s motivation, nor do any of the other 19th-century works I’ve consulted. The idea that he wanted to keep the kids quiet while he took a break is entirely a modern inference. It’s probably wrong—at best it’s unattested—and yet it answers a need of readers today. In the same spirit, many authors confront the question that got me started on this quest: How did Büttner do the math? Bell is adamant that Büttner knew the real formula beforehand; others say he learned the trick only when Gauss explained it to him. An example of the latter position is the following account written in 2001 by three fifth-grade students, Ryan, Jordan and Matthew: When Gauss was in element -ary school his teacher Master Buttner did not really like math so he did not spend a lot of time on the subject . One of the problems his teacher gave the class was “add all the whole numbers from I to 100”. His teacher Master Büttner was amazed that Gauss could add all the whole numbers 1 to 100 in his head . Master Büttner didn’t believe Gauss could do it, so he made him show the class how he did it. Gauss showed Master Büttner how to do it and Master Büttner was amazed at what Gauss just did. Am I being unfair in matching up Eric Temple Bell against three fifth-graders? Unfair to which party? Both offer interpretations that can’t be supported by most historical evidence, but Ryan, Jordan and Matthew are closer to the experience of classroom life. SUMMING UP As with the identity of the series, the details of how Gauss solved the prob1cm remain a matter of conjecture. The algorithm that I suggested ----folding the sequence in half, then adding the first and last elements, the second and next-to-last, etc—is not the only possibility. A related but subtly different algorithm is also mentioned by many authors. The idea is to write down the series twice, once forward and once backward, and then add corresponding elements. For the familiar series 1-100 this procedure yields 100 pairs of 101, for a total of 10,100; then, since the original series was duplicated, we need to divide by 2, arriving at the correct answer 5,050. The advantage of this scheme is that it works the same whether the length of the sequence is odd or even, whereas the folding algorithm requires some fussy adjustments to deal with an odd-length series A third approach to the summation problem strikes me as better still. The root idea is that for any finite set of numbers, whether or not the numbers form an arithmetic progression, the sum is equal to the average of all the elements multiplied by the number of elements. Thus if you know the average, you can easily find the sum. For most sets of numbers, this fact is not very useul, because the only way to calculate the average is first to calculate the sum and then divide by the number of elements . For an arithmetic progression, however, there is a shortcut: The average over the entire series is equal to the average of the first and last elements (or the average of any other elements symmetrically arrayed around the midpoint). If this was Gauss’s secret weapon, then his mental multiplication was not 50 x 101 but 100 x 50 1/25OxlOl but 100x50½. All three of these ideas—and a few more besides----have been presented by one author or another as the method that Gauss discovered during his first arithmetic lesson. THE MORAL OF THE TALE The story of Gauss and his conquest of the arithmetic series has a natural appeal to young people. After all, the hero is a child—a child who outwits a “virile brute.” For many students, that is surely an inspiration. But I worry a little that the very constant repetition of stories like this one may leave the impression that mathema-tics is a game suited only to those who go through life continually throwing off sparks of brilliance. On first hearing this fable, most students surely want to imagine themselves in the role of Gauss. Sooner or later, however, most of us discover we are one of the less- distinguished classmates; if we eventually get the right answer, it’s by hard work rather than native genius. I would hope that the story could be told in a way that encourages those students to keep going. And perhaps it can be balanced by other stories showing there’s a place in mathematics for more than one kind of mind. BRIAN HAYES is a Senior Writer for American Scientist. Additional material related to the “Computing Science” column appears in Hayes’s Weblog at http:/bit-player.org Address: 211 Dacian Avenue, Durham, NC 27710 Email: bhayes @amsci.org SOURCE: AMERICAN SCIENTIST Volume 94. 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