Augustus De Morgan

Augustus De Morgan
Born	(1806-06-27)27 June 1806 Madurai, Carnatic, Madras Presidency (present-day India)
Died	18 March 1871(1871-03-18) (aged 64) London, England
Nationality	British
Alma mater	Trinity College, Cambridge
Known for	De Morgan's laws De Morgan algebra De Morgan hierarchy Relation algebra Universal algebra
Scientific career
Fields	Mathematician and Logician
Institutions	University College London University College School
Academic advisors	John Philips Higman George Peacock William Whewell
Notable students	Edward Routh James Joseph Sylvester Frederick Guthrie William Stanley Jevons Jacob Waley Ada Lovelace Walter Bagehot Richard Holt Hutton Francis Guthrie Stephen Joseph Perry Numa Edward Hartog Henry Roscoe Arthur Cohen Thomas Hodgkin George Jessel
Notes
He was the father of William De Morgan.

Augustus De Morgan (1806–1871) was a British mathematician and logician best known for formulating De Morgan's laws. De Morgan is also known for coining the term "mathematical induction" and for formalizing the underlying principles of induction. De Morgan's contributions to logic have been used in set theory, probability theory, computer science, and other fields.

Biography

Childhood

Augustus De Morgan was born in Madurai, in the Carnatic region of India, in 1806. His father was Lieutenant-Colonel John De Morgan (1772–1816), who held various appointments in the service of the East India Company, and his mother, Elizabeth (née Dodson, 1776–1856), was the daughter of John Dodson and granddaughter of James Dodson, who computed a table of anti-logarithms (inverse logarithms). Augustus De Morgan became blind in one eye within a few months of his birth. His family moved to England when Augustus was seven months old. As his father and grandfather had both been born in India, De Morgan used to say that he was neither English nor Scottish nor Irish, but a Briton "unattached," using the technical term applied to an undergraduate of Oxford or Cambridge who was not a member of any one of the colleges.

When De Morgan was ten years old, his father died. His mathematical talents went unnoticed until he was fourteen, when a family friend discovered him making an elaborate drawing of a figure from one of Euclid's works with a ruler and compasses.

He received his secondary education from Mr. Parsons, a fellow of Oriel College, Oxford, who preferred classics to mathematics. De Morgan's mother was an active and passionate member of the Church of England and wanted her son to become a church official, but by this time, De Morgan had begun to show his non-conforming disposition. He became an atheist.

There is a word in our language with which I shall not confuse this subject, both on account of the dishonourable use which is frequently made of it, as an imputation thrown by one sect upon another, and of the variety of significations attached to it. I shall use the word Anti-Deism to signify the opinion that there does not exist a Creator who made and sustains the Universe.

— Augustus De Morgan, An Essay on Probabilities, and Their Application to Life Contingencies and Insurance Offices

Education

In 1823, at the age of sixteen, De Morgan enrolled in Trinity College, Cambridge. There he met George Peacock and William Whewell, who allegedly became his lifelong friend. From Peacock, he derived an interest in the renovation of algebra, and from Whewell, an interest in the renovation of logic—the two subjects of his future life work. His college tutor was John Philips Higman.

At college, he played the flute recreationally and was prominent in musical clubs.

He placed fourth in the Mathematical Tripos, which entitled him to the degree of Bachelor of Arts. To take the higher degree of Master of Arts and thereby become eligible for a fellowship, he needed to pass a theological test. De Morgan felt a strong objection to signing any such test, although he had been brought up in the Church of England. Around 1875, the requirement of theological tests for academic degrees was abolished by the Universities of Oxford and Cambridge Act 1859. Unable to progress in academia, De Morgan entered Lincoln's Inn to pursue law.

Career

London University, 1827-1831

De Morgan then decided to take up residence in London since he much preferred teaching mathematics over reading law. Around this time, the movement to found London University (now University College London) took shape. The two ancient universities of Oxford and Cambridge were so guarded by theological tests that no Jew or dissenter outside the Church of England could enter as a student, much less be appointed to any office. A body of liberal-minded men resolved to establish a university in London on the principle of religious neutrality. De Morgan, then 22 years old, was appointed professor of mathematics. His introductory lecture, "On the Study of Mathematics," is a discourse on mental education of permanent value and has been recently reprinted in the United States.

The London University was a new institution, and the relations between the Council of Management, the Senate of Professors, and the body of students were not well defined. A dispute arose between the professor of anatomy and his students, and because of the action taken by the council, several professors resigned, headed by De Morgan. Another professor of mathematics was appointed, who drowned a few years later. De Morgan was invited to return to his chair, where he stayed for thirty years.

The Society for the Diffusion of Useful Knowledge

The same body of reformers—headed by Lord Brougham, a Scotsman eminent both in science and politics who had instituted the London University—founded a Society for the Diffusion of Useful Knowledge around the same time. Its goal was to spread scientific knowledge with cheap and clearly written treatises by the best writers of the time. One of its most voluminous and effective writers was De Morgan. He wrote The Differential and Integral Calculus, which was published by the Society, as well as one-sixth of the articles in the Penny Cyclopedia. When De Morgan came to live in London, he found a congenial friend in William Frend. Both were arithmeticians and actuaries, and their religious views were somewhat similar, although their mathematical views differed on account of Frend's rejection of the use of negative numbers. Frend lived in what was then a suburb of London, in a country house formerly occupied by Daniel Defoe and Isaac Watts. De Morgan, with his flute, was a welcome visitor.

Private tutor

Following his first resignation from London University, De Morgan started his work as a private tutor. One of his early students was Jacob Waley. He would tutor Ada Lovelace from 1840 through 1842, primarily via correspondence.

Royal Astronomical Society

De Morgan became involved with the Astronomical Society of London in 1928. He would be appointed honorary secretary in 1931, the year in which it received its Royal Charter and became the Royal Astronomical Society. He would continue as secretary for 18 years and remain actively involved in the Society for 30 years.

London University, 1836-1866

The London University, of which De Morgan was a professor, was a different institution from the University of London. The University of London was founded about ten years later by the government for the purpose of granting degrees after examination without any qualification as to residence. The London University was thus affiliated with the University of London as a teaching college, and its name was changed to University College.

During his time at University College, De Morgan was a highly successful mathematics teacher. His style was to lecture for an hour, and at the close of each lecture, he would give out a number of problems and examples that were illustrative of the lecture subject; his students were required to work on them and bring him the results, which he looked over and returned revised before the next lecture. In De Morgan's opinion, a thorough comprehension of mathematical principles was far more important than an ability to analytically apply half-understood principles to particular cases.

During this period, he also promoted the work of the self-taught Indian mathematician Ramchundra, who has been called De Morgan's Ramanujan. He supervised the publication in London of Ramchundra's book, Treatise on Problems of Maxima and Minima, in 1859. In his preface to that edition, De Morgan wrote:

On examining this work I saw in it, not merely merit worthy of encouragement, but merit of a peculiar kind, the encouragement of which, as it appeared to me, was likely to promote native effort towards the restoration of the native mind in India.

In the same preface, he acknowledged his awareness of the Indian tradition of logic and later wrote again, in 1860, of its significance:

"The two races which have founded the mathematics, those of the Sanscrit and Greek languages, have been the two which have independently formed systems of logic.

Though the sophistication of Indian logical thought had been brought to the attention of Western mathematicians by a number of authors beginning in the late 18th century, it is not known whether this had any influence on De Morgan's own work. Mary Boole, however, claimed a profound influence—via her uncle George Everest—of Indian thought in general and Indian logic, in particular, on George Boole, as well as on De Morgan and Charles Babbage:

Think what must have been the effect of the intense Hinduizing of three such men as Babbage, De Morgan, and George Boole on the mathematical atmosphere of 1830–65. What share had it in generating the vector analysis and the mathematics by which investigations in physical science are now conducted?

Jonardon Ganeri has observed that it was this period of the mid-nineteenth century pointed to by Mary Boole that saw George Boole and Augustus De Morgan make their pioneering applications of algebraic ideas to the formulation of logic (algebraic logic and Boolean logic) and has suggested that these figures were likely to have been aware of the Indian system of logic and, in turn, that their awareness of the shortcomings of propositional logic as it was then formulated may have contributed to their willingness to look beyond their own logical tradition.

London Mathematical Society

Arthur Cowper Ranyard and George Campbell De Morgan, De Morgan's son, conceived the idea of founding a mathematical society in London, where mathematical papers would be not only received (as by the Royal Society) but also read and discussed. The first meeting of the London Mathematical Society was held at University College in 1865. De Morgan was the first president and his son was the first secretary. Early members included Benjamin Gompertz, De Morgan's personal friend, and James Joseph Sylvester, De Morgan's former student.

Personal life

Augustus was one of seven children, four of whom survived to adulthood. These siblings were Eliza (1801–1836), who married Lewis Hensley, a surgeon living in Bath; George (1808–1890), a barrister-at-law who married Josephine, daughter of Vice Admiral Josiah Coghill, 3rd Baronet Coghill; and Campbell Greig (1811–1876), a surgeon at the Middlesex Hospital.

In the autumn of 1837, De Morgan married Sophia Elizabeth Frend (1809–1892), the eldest daughter of William Frend (1757–1841), and Sarah Blackburne (1779–?), a granddaughter of Francis Blackburne (1705–1787), Archdeacon of Cleveland.

De Morgan had three sons and four daughters, including fairytale author Mary De Morgan. His eldest son was the potter William De Morgan. His second son, George, acquired distinction in mathematics at University College and the University of London.

De Morgan was full of personal peculiarities. On the occasion of the installation of his friend, Lord Brougham, as Rector of the University of Edinburgh, the Senate offered to confer on him the honorary degree of LL. D.; he declined the honour as a misnomer. He humorously described himself using the Latin phrase 'Homo paucarum literarum' (man of few letters), reflecting his modesty about his extensive contributions to mathematics and logic.

He disliked the provinces outside London, and while his family enjoyed the seaside and men of science were having a good time at a meeting of the British Association in the country, he remained in the hot and dusty libraries of the metropolis. He said that he felt like Socrates, who declared that the farther he was from Athens, the farther he was from happiness. He never sought to become a Fellow of the Royal Society, and he never attended a meeting of the Society; he said that he had no ideas or sympathies in common with the physical philosopher. His attitude was possibly due to his physical infirmity, which prevented him from being either an observer or an experimenter. He never voted at an election, and he never visited the House of Commons, the Tower of London, or Westminster Abbey.

Retirement and death

Augustus De Morgan.

In 1866, the chair of mental philosophy at University College fell vacant. James Martineau, a Unitarian clergyman and professor of mental philosophy, was recommended formally by the Senate to the council, but in the council, there were some who objected to a Unitarian clergyman and others who objected to theistic philosophy. A layman of the school of Bain and Spencer was appointed. De Morgan considered that the old standard of religious neutrality had been hauled down and immediately resigned. He was now 60 years old. His pupils secured him a pension of £500 p.a., but misfortunes followed. Two years later, his son George—the "younger Bernoulli," as Augustus loved to hear him call him, in allusion to the eminent father-and-son mathematicians of that name—died. This blow was followed by the death of a daughter. Five years after his resignation from University College, De Morgan died of nervous prostration on March 18, 1871.

Works

De Morgan was a prolific writer, contributing over 600 articles to the Penny Cyclopedia alone. Mainly through the efforts of Peacock and Whewell, a Philosophical Society had been inaugurated at Cambridge, and De Morgan contributed four memoirs to its transactions on the foundations of algebra and an equal number on formal logic. The best presentation of his view of algebra is found in a volume entitled Trigonometry and Double Algebra, published in 1849, and his earlier view of formal logic is found in a volume published in 1847. His most distinctive work is styled A Budget of Paradoxes; it originally appeared as letters in the columns of the Athenæum journal; it was revised and extended by De Morgan in the last years of his life and was published posthumously by his widow.

Correspondence

De Morgan was a brilliant and witty writer, whether as a controversialist or as a correspondent. In his time, there flourished two Sir William Hamiltons who have often been conflated. One was William Hamilton, a Scotsman, professor of logic and metaphysics at the University of Edinburgh; the other was a knight (that is, won the title), an Irishman, professor of astronomy at the University of Dublin.

Be it known unto you that I have discovered that you and the other Sir W. H. are reciprocal polars with respect to me (intellectually and morally, for the Scottish baronet is a polar bear, and you, I was going to say, are a polar gentleman). When I send a bit of investigation to Edinburgh, the W. H. of that ilk says I took it from him. When I send you one, you take it from me, generalize it at a glance, bestow it thus generalized upon society at large, and make me the second discoverer of a known theorem.

The correspondence of De Morgan with W. R. Hamilton, the mathematician, extended over twenty-four years; it contains discussions not only of mathematical matters but also of subjects of general interest. It is marked by geniality on the part of Hamilton and by wit on the part of De Morgan. The following is a specimen:

Hamilton wrote:

My copy of Berkeley's work is not mine; like Berkeley, you know, I am an Irishman.

De Morgan replied:

Your phrase 'my copy is not mine' is not a bull. It is perfectly good English to use the same word in two different senses in one sentence, particularly when there is usage. Incongruity of language is no bull, for it expresses meaning. But incongruity of ideas (as in the case of the Irishman who was pulling up the rope, and finding it did not finish, cried out that somebody had cut off the other end of it) is the genuine bull.

Trigonometry and Double Algebra

De Morgan's work entitled Trigonometry and Double Algebra consists of two parts, the former of which is a treatise on trigonometry and the latter a treatise on generalized algebra, which he called "double algebra." The first stage in the development of algebra is arithmetic, where only natural numbers and symbols of operations such as +, ×, etc. are used. The next stage is universal arithmetic, where letters appear instead of numbers so as to denote numbers universally, and the processes are conducted without knowing the values of the symbols. Let a and b denote any natural numbers. An expression such as a − b may still be impossible, so in universal arithmetic there is always a proviso, provided the operation is possible. The third stage is single algebra, where the symbol may denote a quantity forwards or a quantity backwards and is adequately represented by segments on a straight line passing through an origin. Negative quantities are then no longer impossible; they are represented by the backward segment. But an impossibility still remains in the latter part of such an expression as a + b√−1, which arises in the solution of the quadratic equation. The fourth stage is double algebra. The algebraic symbol denotes, in general, a segment of a line in a given plane. It is a double symbol because it involves two specifications, namely, length and direction, and √−1 is interpreted as denoting a quadrant. The expression a + b√−1 then represents a line in the plane having an abscissa a and an ordinate b. Argand and Warren have carried double algebra so far, but they were unable to interpret on this theory such an expression as e^a√−1. De Morgan attempted it by reducing such an expression to the form b + q√−1, and he considered that he had shown that it could always be so reduced. The remarkable fact is that this double algebra satisfies all the fundamental laws above enumerated, and as every apparently impossible combination of symbols has been interpreted, it looks like the complete form of algebra. In Chapter 6, he introduced hyperbolic functions and discussed the connection between common and hyperbolic trigonometry.

If the above theory is true, the next stage of development ought to be triple algebra, and if a + b√−1 truly represents a line in a given plane, it ought to be possible to find a third term which that, added to the above, would represent a line in space. Argand and some others guessed that it was a + b√−1 + c√−1^√−1, although this contradicts the truth established by Euler that √−1^√−1 = e^−π/2. De Morgan and many others worked hard at the problem, but nothing came of it until the problem was taken up by Hamilton. We now see the reason clearly: The symbol of double algebra denotes not a length and a direction but a multiplier and an angle. In it, the angles are confined to one plane. Hence, the next stage will be quadruple algebra, when the axis of the plane is made variable. And this gives the answer to the first question: double algebra is nothing but analytical plane trigonometry, and this is why it has been found to be the natural analysis for alternating currents. But De Morgan never got this far. He died with the belief that "double algebra must remain as the full development of the conceptions of arithmetic, so far as those symbols are concerned which arithmetic immediately suggests."

In Book II, Chapter II, following the above quoted passage about the theory of symbolic algebra, De Morgan proceeds to give an inventory of the fundamental symbols of algebra, and also an inventory of the laws of algebra. The symbols are $0$, $1$, $+$, $-$, $\times$, $\div$, $()$⁽⁾, and letters; these only, all others are derived. As De Morgan explains, the last of these symbols represents writing a latter expression in superscript over and after a former. His inventory of the fundamental laws is expressed under fourteen heads, but some of them are merely definitions. The preceding list of symbols is the matter under the first of these heads. The laws proper may be reduced to the following, which, as he admits, are not all independent of one another, "but the unsymmetrical character of the exponential operation, and the want of the connecting process of $+$ and $\times$ ... renders it necessary to state them separately":

1. Identity laws. $a=0+a=1\times a$, $=a+0=a-0=a\times 1=a\div 1$, $=0+1\times a$
2. Law of signs. $+(+a)=+a,$ $+(-a)=-a,$ $-(+a)=-a,$ $-(-a)=+a,$ $\times (\times a)=\times a,$ $\times (\div a)=\div a,$ $\div (\times a)=\div a,$ $\div (\div a)=\times a$
3. Commutative law. $a+b=b+a,$ $a\times b=b\times a$
4. Distributive law. $a(b+c)=ab+ac,$ $a(b-c)=ab-ac,$ $(b+c)\div a=(b\div a)+(c\div a),$ $(b-c)\div a=(b\div a)-(c\div a)$
5. Index laws. $a^{0}=1,$ $a^{1}=a,$ $(a\times b)^{c}=a^{c}\times b^{c},$ $a^{b}\times a^{c}=a^{b+c},$ $(a^{b})^{c}=a^{b\times c}$

De Morgan professes to give a complete inventory of the laws which the symbols of algebra must obey, for he says, "Any system of symbols which obeys these rules and no others—except they be formed by combination of these rules—and which uses the preceding symbols and no others—except they be new symbols invented in abbreviation of combinations of these symbols—is symbolic algebra." From his point of view, none of the above principles are rules; they are formal laws, that is, arbitrarily chosen relations to which the algebraic symbols must be subject. He does not mention the law, which had already been pointed out by Gregory, namely, $(a+b)+c=a+(b+c),(ab)c=a(bc)$ and to which was afterwards given the name Law of association. If the commutative law fails, the associative may hold good; but not vice versa. It is an unfortunate thing for the symbolist or formalist that in universal arithmetic $m^{n}$ is not equal to $n^{m}$; for then the commutative law would have full scope. Why does he not give it full scope? Because the foundations of algebra are, after all, real not formal, material not symbolic. To the formalists the index operations are exceedingly refractory, in consequence of which some take no account of them, but relegate them to applied mathematics. To give an inventory of the laws which the symbols of algebra must obey is an impossible task, and reminds one not a little of the task of those philosophers who attempt to give an inventory of the a priori knowledge of the mind.

George Peacock's theory of algebra was much improved by D. F. Gregory, a younger member of the Cambridge School, who laid stress not on the permanence of equivalent forms but on the permanence of certain formal laws. This new theory of algebra as the science of symbols and of their laws of combination was carried to its logical issue by De Morgan, and his doctrine on the subject is still followed by English algebraists in general. Thus, George Chrystal founds his Textbook of Algebra on De Morgan's theory, although an attentive reader may remark that he practically abandons it when he takes up the subject of infinite series. De Morgan's theory is stated in Book II, Chapter II, headed "On symbolic algebra," he writes:

In abandoning the meanings of symbols, we also abandon those of the words which describe them. Thus addition is to be, for the present, a sound void of sense. It is a mode of combination represented by $+$; when $+$ receives its meaning, so also will the word addition. It is most important that the student should bear in mind that, with one exception, no word nor sign of arithmetic or algebra has one atom of meaning throughout this chapter, the object of which is symbols, and their laws of combination, giving a symbolic algebra which may hereafter become the grammar of a hundred distinct significant algebras. If any one were to assert that $+$ and $-$ might mean reward and punishment, and $A$, $B$, $C$, etc. might stand for virtues and vices, the reader might believe him, or contradict him, as he pleases—but not out of this chapter.

The one exception above noted, which has some share of meaning, is the sign $=$ placed between two symbols, as in $A=B$. It indicates that the two symbols have the same resulting meaning, by whatever different steps are taken. That $A$ and $B$, if quantities, are the same amount of quantity; that if operations, they are of the same effect, etc.

Formal Logic

Further information: De Morgan's laws

When the study of mathematics revived at the University of Cambridge, so did the study of logic. The moving spirit was Whewell, the Master of Trinity College, whose principal writings were a History of the Inductive Sciences and Philosophy of the Inductive Sciences. Doubtless De Morgan was influenced in his logical investigations by Whewell, but other influential contemporaries were Sir William Rowan Hamilton in Dublin and George Boole in Cork. De Morgan's work, Formal Logic, published in 1847, is principally remarkable for his development of the numerically definite syllogism. The followers of Aristotle say that from two particular propositions, such as Some M's are A's and Some M's are B's, nothing follows of necessity about the relation of the A's and B's. But they go further and say that in order that any relation between the A's and B's may follow of necessity, the middle term must be taken universally in one of the premises. De Morgan pointed out that from Most M's are A's and Most M's are B's, it follows by necessity that some A's are B's, and he formulated the numerically definite syllogism, which puts this principle in exact quantitative form. Suppose that the number of the M's is $m$, of the M's that are A's is $a$, and of the M's that are B's is $b$; then there are at least $(a+b-m)$ A's that are B's. Suppose that the number of souls on board a steamer was 1000, that 500 were in the saloon, and 700 were lost. It follows, of necessity, that at least 700 + 500 – 1000, that is, 200, saloon passengers were lost. This single principle suffices to prove the validity of all the Aristotelian moods. It is therefore a fundamental principle in necessary reasoning.

By then, De Morgan had made a great advance by introducing quantification of the terms. At that time, Sir William Hamilton was teaching in Edinburgh a doctrine of the quantification of the predicate, and a correspondence sprang up. However, De Morgan soon perceived that Hamilton's quantification was of a different character; that it meant, for example, substituting the two forms. The whole of A is the whole of B, and the whole of A is a part of B for the Aristotelian form. All A's are B's. Hamilton thought that he had placed the keystone in the Aristotelian arch, as he phrased it. Although it must have been a curious arch that could stand for 2000 years without a keystone, as a consequence, he had no room for De Morgan's innovations. He accused De Morgan of plagiarism, and the controversy raged for years in the columns of the Athenæum and in the publications of the two writers.

The memoirs on logic that De Morgan contributed to the Transactions of the Cambridge Philosophical Society subsequent to the publication of his book Formal Logic are by far the most important contributions that he made to the science, especially his fourth memoir, in which he begins work in the broad field of the "logic of relatives."

Budget of Paradoxes

In the introduction to A Budget of Paradoxes, De Morgan explains what he means by the word:

A great many individuals, ever since the rise of the mathematical method, have, each for himself, attacked its direct and indirect consequences. I shall call each of these persons a paradoxer, and his system a paradox. I use the word in the old sense: a paradox is something which is apart from general opinion, either in subject matter, method, or conclusion. Many of the things brought forward would now be called crotchets, which is the nearest word we have to old paradox. But there is this difference, that by calling a thing a crotchet we mean to speak lightly of it; which was not the necessary sense of paradox. Thus in the 16th century many spoke of the earth's motion as the paradox of Copernicus and held the ingenuity of that theory in very high esteem, and some I think who even inclined towards it. In the seventeenth century the deprivation of meaning took place, in England at least.

How can the sound paradoxer be distinguished from the false paradoxer? De Morgan supplies the following test:

The manner in which a paradoxer will show himself, as to sense or nonsense, will not depend upon what he maintains, but upon whether he has or has not made a sufficient knowledge of what has been done by others, especially as to the mode of doing it, a preliminary to inventing knowledge for himself... New knowledge, when to any purpose, must come by contemplation of old knowledge, in every matter which concerns thought; mechanical contrivance sometimes, not very often, escapes this rule. All the men who are now called discoverers, in every matter ruled by thought, have been men versed in the minds of their predecessors and learned in what had been before them. There is not one exception.

The Budget consists of a review of a large collection of paradoxical books that De Morgan had accumulated in his own library, partly by purchase at bookstands, partly from books sent to him for review, and partly from books sent to him by the authors. He gives the following classification: squarers of the circle, trisectors of the angle, duplicators of the cube, constructors of perpetual motion, subverters of gravitation, stagnators of the earth, and builders of the universe. You will still find specimens of all these classes in the New World and in the new century. De Morgan gives his personal knowledge of paradoxers.

I suspect that I know more of the English class than any man in Britain. I never kept any reckoning: but I know that one year with another?  and less of late years than in earlier time? – I have talked to more than five in each year, giving more than a hundred and fifty specimens. Of this I am sure, that it is my own fault if they have not been a thousand. Nobody knows how they swarm, except those to whom they naturally resort. They are in all ranks and occupations, of all ages and characters. They are very earnest people, and their purpose is bona fide, the dissemination of their paradoxes. A great many – the mass, indeed – are illiterate, and a great many waste their means, and are in or approaching penury. These discoverers despise one another.

A paradoxer to whom De Morgan paid the compliment that Achilles paid Hector – to drag him round the walls again and again – was James Smith, a successful merchant of Liverpool. He found $\pi =3{\tfrac {1}{8}}$. His mode of reasoning was a curious caricature of the reductio ad absurdum of Euclid. He said let $\pi =3{\tfrac {1}{8}}$, and then showed that on that supposition, every other value of $\pi$ must be absurd. Consequently, $\pi =3{\tfrac {1}{8}}$ is the true value. The following is a specimen of De Morgan's dragging around the walls of Troy:

Mr. Smith continues to write me long letters, to which he hints that I am to answer. In his last of 31 closely written sides of note paper, he informs me, with reference to my obstinate silence, that though I think myself and am thought by others to be a mathematical Goliath, I have resolved to play the mathematical snail, and keep within my shell. A mathematical snail! This cannot be the thing so called which regulates the striking of a clock; for it would mean that I am to make Mr. Smith sound the true time of day, which I would by no means undertake upon a clock that gains 19 seconds odd in every hour by false quadrative value of $\pi$. But he ventures to tell me that pebbles from the sling of simple truth and common sense will ultimately crack my shell, and put me hors de combat. The confusion of images is amusing: Goliath turning himself into a snail to avoid $\pi =3{\tfrac {1}{8}}$ and James Smith, Esq., of the Mersey Dock Board: and put hors de combat by pebbles from a sling. If Goliath had crept into a snail shell, David would have cracked the Philistine with his foot. There is something like modesty in the implication that the crack-shell pebble has not yet taken effect; it might have been thought that the slinger would by this time have been singing – And thrice [and one-eighth] I routed all my foes, And thrice [and one-eighth] I slew the slain.

In the region of pure mathematics, De Morgan could easily detect the false from the true paradox, but he was not so proficient in the field of physics. His father-in-law was a paradoxer, and his wife was a paradoxer, and in the opinion of the physical philosophers, De Morgan himself scarcely escaped. His wife wrote a book describing the phenomena of spiritualism, table-rapping, table-turning, etc., and De Morgan wrote a preface in which he said that he knew some of the asserted facts, believed others on testimony, but did not pretend to know whether they were caused by spirits or had some unknown and unimagined origin. In this alternative, he left out ordinary material causes. Faraday delivered a lecture on spiritualism, in which he laid it down that in the investigation we ought to set out with the idea of what is physically possible or impossible; De Morgan did not believe this.

Relations

De Morgan developed the calculus of relations in his Syllabus of a Proposed System of Logic (1966: 208–46), first published in 1860. De Morgan was able to show that reasoning with syllogisms could be replaced with the composition of relations. The calculus was described as the logic of relatives by Charles Sanders Peirce, who admired De Morgan and met him shortly before his death. The calculus was further extended in the third volume of Ernst Schröder's Vorlesungen über die Algebra der Logik. Binary relations, especially order theory, proved critical to the Principia Mathematica of Bertrand Russell and Alfred North Whitehead. In turn, this calculus became the subject of much further work, starting in 1940, by Alfred Tarski and his colleagues and students at the University of California.

Spiritualism

De Morgan later in his life became interested in the phenomenon of spiritualism. In 1849, he investigated clairvoyance and was impressed by the subject. He later carried out paranormal investigations in his own home with the American medium, Maria Hayden. The result of those investigations was later published by his wife, Sophia. De Morgan believed that his career as a scientist might have been affected if he had revealed his interest in the study of spiritualism, so he helped to publish the book anonymously. The book was published in 1863, titled From Matter to Spirit: The Result of Ten Years Experience in Spirit Manifestations.

According to historian Janet Oppenheim, De Morgan's wife Sophia was a convinced spiritualist, but De Morgan shared a third–way position on spiritualist phenomena, which Oppenheim defined as a "wait-and-see position"; he was neither a believer nor a skeptic. Instead, his viewpoint was that the methodology of the physical sciences does not automatically exclude psychic phenomena and that such phenomena may be explainable in time by the possible existence of natural forces that physicists have not yet identified.

In the preface to From Matter to Spirit (1863), De Morgan stated:

Thinking it very likely that the universe may contain a few agencies – say half a million – about which no man knows anything, I can not but suspect that a small proportion of these agencies – say five thousand – may be severally competent to the production of all the [spiritualist] phenomena, or may be quite up to the task among them. The physical explanations which I have seen are easy, but miserably insufficient: the spiritualist hypothesis is sufficient, but ponderously difficult. Time and thought will decide, the second asking the first for more results of trial.

Psychical researcher John Beloff wrote that De Morgan was the first notable scientist in Britain to take an interest in the study of spiritualism, and his studies had influenced the decision of William Crookes to also study spiritualism. Beloff also claims that De Morgan was an atheist, and so he was debarred from a position at Oxford or Cambridge.

Legacy

Beyond his mathematical legacy, the headquarters of the London Mathematical Society are called De Morgan House, and the top prize awarded by the Society is the De Morgan Medal.

The student society of the Mathematics Department of University College London is called the Augustus De Morgan Society.

The lunar crater De Morgan is named after him.

Selected writings

• An Explanation of the Gnomonic Projection of the Sphere. London: Baldwin. 1836.
• Elements of Trigonometry, and Trigonometrical Analysis. London: Taylor & Walton. 1837a.
• The Elements of Algebra. London: Taylor & Walton. 1837b.
• An Essay on Probabilities, and Their Application to Life Contingencies and Insurance Offices. London: Longman, Orme, Brown, Green & Longmans. 1838.
• The Elements of Arithmetic. London: Taylor & Walton. 1840a.
• First Notions of Logic, Preparatory to the Study of Geometry. London: Taylor & Walton. 1840b.
• The Differential and Integral Calculus. London: Baldwin. 1842.
• The Globes, Celestial and Terrestrial. London: Malby & Co. 1845.
• Formal Logic or The Calculus of Inference, Necessary and Probable. London: Taylor & Walton. 1847.
• Trigonometry and Double Algebra. London: Taylor, Walton & Malbery. 1849.
• Syllabus of a Proposed System of Logic. London: Walton & Malbery. 1860.
• A Budget of Paradoxes. London: Longmans, Green. 1872.

See also

• History of Grandi's series
• Murphy's law
• Squaring the circle

References

Sources

• This article incorporates text from this source, which is in the public domain. Macfarlane, Alexander (1916). Lectures on Ten British Mathematicians of the Nineteenth Century (PDF). New York: John Wiley and Sons.
• Beloff, John (1997). Parapsychology: A Concise History. Palgrave Macmillan. ISBN 978-0-312-17376-0. He seems an unlikely convert considering that his atheistic views had debarred him from a position at Oxford or Cambridge but his involvement with spiritualism was partly due to his wife, Sophia.
• Conklin, Groff (March 1955). "Galaxy's 5 Star Shelf". Galaxy Science Fiction.
• De Morgan, Sophia Elizabeth; De Morgan, Augustus (1882). Memoir of Augustus De Morgan: With Selections from His Letters. Longmans, Green, and Company. ISBN 978-1-108-01447-2. So you called me an atheist vagabond, fancying that Voltaire was an atheist : he was, in fact, theistic to bigotry, and anti-revolutionist to the same extent.
• Hollings, Christopher; Martin, Ursula; Rice, Adrian (2017). "The Lovelace-De Morgan mathematical correspondence: A critical re-appraisal". Historia Mathematica. 44 (3): 202–231. doi:10.1016/j.hm.2017.04.001.
• Karpinski, Louis (1916). "Review: A Budget of Paradoxes (2nd edn.), by Augustus De Morgan". Bull. Amer. Math. Soc. 22 (9): 468–471. doi:10.1090/s0002-9904-1916-02839-4.
• Merrill, Daniel D. (2012). Augustus De Morgan and the Logic of Relations. Springer Science & Business Media. ISBN 978-94-009-2047-7.
• Nelson, Geoffrey K. (1969). Spiritualism and Society. Routledge & K. Paul. ISBN 9780710062529.
• Oppenheim, Janet (1985). The Other World: Spiritualism and Psychical Research in England, 1850–1914. p. 335. ISBN 0-521-34767-X.
• Rice, Adrian Clifford (1997). Augustus De Morgan and the development of university mathematics in London in the nineteenth century (Thesis). Middlesex University.
• Richards, Joan L. (1987). "Augustus De Morgan, the History of Mathematics, and the Foundations of Algebra". Isis. 78 (1): 6–30. doi:10.1086/354328.
• Simmons, Charlotte (2011). "Augustus De Morgan Behind the Scenes". The College Mathematics Journal. 42 (1): 33–40. doi:10.4169/college.math.j.42.1.033.
• https://www.britannica.com/biography/Augustus-De-Morgan

Further reading

• Jevons, William Stanley (1878). "Augustus De Morgan" . Encyclopædia Britannica. Vol. VII (9th ed.). pp. 64–67.
• De Morgan, Sophia Elizabeth (1882). Memoir of Augustus De Morgan. London: Longmans, Green and Company. Augustus De Morgan.
• Stephen, Leslie, ed. (1888). "De Morgan, Augustus" . Dictionary of National Biography. Vol. 14. London: Smith, Elder & Co.
•  Cousin, John William (1910), "De Morgan, Augustus", A Short Biographical Dictionary of English Literature, London: J. M. Dent & Sons – via Wikisource
• De Morgan, A., 1966. Logic: On the Syllogism and Other Logical Writings. Heath, P., ed. Routledge. A useful collection of De Morgan's important writings on logic.
• Grattan-Guinness, Ivor (2000). The Search for Mathematical Roots 1870–1940. Princeton University Press.

External links

• Works by Augustus De Morgan at Project Gutenberg
• Works by or about Augustus De Morgan at Internet Archive
• Works by Augustus De Morgan at LibriVox (public domain audiobooks)
• O'Connor, John J.; Robertson, Edmund F., "Augustus De Morgan", MacTutor History of Mathematics Archive, University of St Andrews
• Papers of Augustus De Morgan held by Senate House Library, University of London
• Library of Augustus De Morgan
• "Archival material relating to Augustus De Morgan". UK National Archives.
• Portraits of Augustus De Morgan at the National Portrait Gallery, London