on this website

of the pages of this website

a summary of my 2015 / 2017 essay about Hamilton’s private life

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My essays can be read in the BookReader (developed by the Internet Archive),

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** To admire is, to me, questionless, the highest pleasure in life.**

— Sir William Rowan Hamilton, 1838

This is the entrance page to a website about the private life of **Sir William Rowan Hamilton (1805-1865)**, “a labour-loving and truth-loving man.”

And of his wife**Lady Helena Maria Hamilton, née Bayly (1804-1869)**, “the centre round which the pleasures, the duties, and the hopes of home were gathered.”

Also of**Catherine Disney (1800-1853)**, whose terrible fate influenced the people who loved her.

And of his wife

Also of

This website is created and maintained by

**Anne van Weerden, BSc**

A contact form can be found at the bottom of this page.

A contact form can be found at the bottom of this page.

**A Victorian Marriage : Sir William Rowan Hamilton**

The essay about Hamilton’s private life as pdf or epub, background information, and further publications

**Catherine Disney : a biographical sketch**

The sketch as pdf or epub, and background information

**Paintings and photos of some of the people in Hamilton’s biography**

Family, friends and colleagues

**This page contains anything not at home in the other pages**

From subjects belonging to Hamilton’s story,

to my own interests and doings.

**Sir William Rowan Hamilton** was Ireland’s greatest mathematician, Andrews professor of Astronomy at Trinity College Dublin, and Royal Astronomer of Ireland. Born in Dublin in 1805 and grown up and educated in Trim, having been a child prodigy Hamilton became Astronomy professor in 1827, shortly before his final exams, and then moved into Dunsink Observatory where he would live for the rest of his life. In April 1833 he married Helena Maria Bayly, born in 1804 and living at Bayly Farm in Nenagh Tipperary. It was a good marriage, blessed with three children; William Edwin was born in 1834, Archibald Henry in 1835, and Helen Eliza Amelia in 1840. They became Sir and Lady Hamilton when in 1835 Hamilton was knighted for his discovery of conical refraction. Hamilton died in 1865 at the Observatory, and Lady Hamilton in 1869 in Donnybrook. They both were buried at Mount Jerome Cemetery.

Hamilton’s work is highly praised;
**below** a short overview is given of the still growing influence of his work. But due to an extraordinary coincidence of circumstances, nowadays the view on the Hamilton couple’s private life is very negative. During their life there already had been gossip in Dublin, but nothing more than there usually is about very famous people in very strict societies, as Ireland and England were in the Victorian era. The real distortions started when in the 1880s Robert Perceval Graves published an enormous biography of Hamilton, and on only six or seven pages criticised Hamilton and the choices he made for himself. These pages started to live a life of their own, and all the highly admiring other two-thousand ones were soon forgotten, including Graves’ very positive remarks about the marriage and about Lady Hamilton, and his emphasizing that Hamilton was not alcoholic, as the local gossip had insisted.

Stated succinctly, Hamilton is now generally assumed to have been an unhappily married **alcoholic**, and Lady Hamilton a neurotic hypochondrial **nobody**. In my 2017 book ** A Victorian Marriage**, actually a history essay, of which a summary is given

Unfortunately, it seems that almost anything could be added to the story of Hamilton’s private life as long as it fitted the caricature of an unhappy and unworldly genius who married a woman who could not handle him, nor the household. And even nowadays new additions still appear. To bring this process to a halt and show the Hamiltons again as the people they were, their life must be reconsidered by returning to the original sources, and told anew. This website is dedicated to that, by discussing details from the Hamilton couple’s private life as was found in their own letters, in Graves’ biography, in descriptions of contemporaries, church records, newspaper articles, and articles and books from those times which can be found in abundance on the Internet Archive and HathiTrust.* Together they show Hamilton as a happily married family man and a very hard-working mathematician, and Lady Hamilton as the wife who made that possible.

* There obviously are more websites showing scanned books, and often very beautiful ones, but these two have searchable scans. A feature absolutely crucial for searches like the ones described here.

I started this website in 2015, when I was writing my first essay about the happy marriage of Sir and Lady Hamilton. It consist of four main pages.

**VictorianMarriage.html** where my two essays, publications and unpublications are listed, and every now and then I write blogposts about for me new details or new insights.

**HamiltonPhotopage.html** is filled with photographs of Hamilton’s family, friends and colleagues, to get some notion of what people looked like in those days, and placing the Hamilton photos into perspective.

**CatherineDisney.html** is dedicated to the very unhappy life of Hamilton’s first love Catherine Disney; I wrote my second book about her. On the one hand to show that it was not at all strange that Hamilton was periodically upset about her fate and that that had nothing to do with his own marriage, but also because her very sad story was in itself worth to be told. Forcing people into marriages they do not want to be in should not be possible anywhere at any time.

**Miscellaneous.html** is partly connected to Hamilton, and partly to my former physics study, which was interrupted when I stumbled on the very strange stories which were told about the Hamiltons.

The website is ongoing work, yet I hope that some day the view on the Hamiltons’ private life becomes as positive as they deserve, and this work will be finished. What I really hope for is that someone will write a **new biography**; for such an extraordinary story three main biographies written in three different times are certainly not too many. I then hope it will be someone with a thorough knowledge of all sides of Hamilton's scientific life, from his mathematics to his metaphysics, combined with theology, psychology, literature and history, who is prepared to take the gossip out of the stories, and will make good use of all the tiny details I found to be incorrect or simply missing. Such a new biography would, in one stroke, change the views on Hamilton. While the mathematicians, physicists, computer scientists, engineers, etc. carry on the work following from Hamilton’s enormous legacy, of which a glimpse is given **below**.

And then a beautiful **costume drama**, in which Hamilton’s love for Catherine Disney is embedded in the terrible story of her life, a love which at the same time did not in any way destroy the happy marriage Hamilton had with Helen Bayly. It will not be easy to depict this very nuanced and intricate story while respecting the people involved, but it can be a scintillating story about a beautiful, talented Disney daughter who was sacrificed on the altar of family pride and was unable to cope with her fate; a kind, humble, yet also very self-assured genius who was far ahead of his time and had to endure the consequences thereof; and a happy and headstrong woman from Nenagh, Tipperary, who with her weak health dared to marry a man like that.

The engraving of the **steam locomotive Hibernia**, built in 1834, shows the state of science a year after Hamilton’s marriage, two years after the publication of his ** Third Supplement to an Essay on the Theory of Systems of Rays** which would lead to Hamiltonian mechanics,* and nine years before Hamilton found the quaternions.

The Dublin and Kingstown Railway was Ireland's first railway.

Copied from the ** Dublin Penny Journal of September 1834**.

Having made his discoveries in a time in which photography, telephone and radio did not exist yet, bicycles were in their infancy and people walked or travelled by horse, carriage, steam train and steamship, Hamilton’s son reported that “Sir W.” was indifferent to contemporary fame, “arising from his conviction that his belonged to a future age entirely.” Hamilton was right, yet little could he know that large parts of his work had to wait until quantum mechancis and the dawn of computers before they would start to blossom.

* For short descriptions and complete transcriptions of the original essay and the three supplements see David Wilkins, **Theory of Systems of Rays**.

However strange it may sound to someone within the Hamilton-bubble, hardly any member of the general public knows about Hamilton. Taking myself as an example, I had earned my bachelors in physics before ever realizing that behind the Hamiltonian there was a man. It was not because of happy youthful naivety; I was fifty-five already when I became a BSc, and had followed the course ‘Advanced Classical Mechanics’, being thus familiar with the Hamiltonian. And when I did hear about the Irish Sir and searched for information about him on the internet I did not like him at all; he had married a local lass because he could not marry the woman he really loved, and made her unhappy by just working on his mathematics and depressedly becoming an alcoholic. How could he do that to her.

I was astounded when I discovered that Hamilton had not married his wife ‘on the rebound,’ and had not at all been alcoholic. Learning more about his life and work I entered the bubble in which Hamilton seems to be omnipresent, and became surprised again why I had not heard of him earlier. Soon it appeared that during his life and in the years shortly thereafter Hamilton was seen as one of the **great mathematicians** as Clement Ingleby called him in 1869, and even as late as 1895 Robert Stawell Ball dedicated a chapter to him in his famous book **Great Astronomers**. Yet although Hamilton’s mechanics was highly praised, as for instance in this 1878 **Leiden dissertation**, it was not known why it would be useful.* And not only his mechanics had to wait, for even longer periods of time no one knew why to use the quaternions outside pure mathematics.

* **Adriaan Kempe 1878**, p 100, proposition III: “For now, the analytic mechanical considerations of Hamilton and Jacobi only have theoretical value.”

It is well-known that after Hamilton’s death in 1865 **Peter Guthrie Tait** continued his work on the quaternions with heart and soul, and in 1872 also his friend **James Clerk Maxwell** had been “getting **converted** to Quaternions.” Even though he wrote his * Treatise on Electricity and Magnetism* in “Cartesian form,” he was “

But not everyone was happy with Maxwell’s use of quaternions, and, coincidentally, the second and darkest volume of Graves’s biography, containing the major part of his lamentations about Hamilton’s drinking alcohol, was published in the same year, 1885, that **Oliver Heaviside** argued in his **article** ‘On the Electromagnetic Wave-surface’ that the **quaternions were superfluous**, that the quaternion product was not at all necessary for physics. **In 1888**, a year before the publication of the third and last volume of the biography, **Josiah Willard Gibbs** sent copies of his **unpublished pamphlet** on **vector analysis** to Heaviside and many other scientists, and the **vector wars** soon followed.* Even though it can easily be argued that Hamilton would never have become engaged in such heated discussions, that he most likely would have welcomed vector analysis as the spin-off of his quaternions, it severely damaged his reputation.

* I did know how much the vector debates harmed Hamilton’s reputation. But until I worked with Kathy Jones on her **Hamilton and Quaternions video**, I had not realised that Heaviside published his criticisms in the same year Graves published the second volume of his biography.

The damage was so thorough that nothing could reverse it any more; it was well-known that **in 1925** Werner Heisenberg* and **in 1926** Erwin Schrödinger published their papers on quantum mechanics with which Hamilton’s mechanics finally found its place in physics; that with the coming of computers, which do not mind long calculations, the quaternions reappeared; that in 1967 **Michael Crowe** showed that vector analysis stemmed directly from the quaternions, yet it was not enough to counteract the negativity; during the twentieth century Hamilton’s name completely disappeared from the public view.

* Heisenberg’s **original paper** did not mention Hamilton’s work, that appeared first in a 1925 article about Heisenberg’s theory by Max Born and Pascual Jordan, **Zur Quantenmechanik**, translated as **On Quantum mechanics**, then in the 1926 **article** Heisenberg wrote with Born and Jordan. Their version became known as ‘matrix mechanics’, that of Schrödinger as ‘wave mechanics’; both versions were later shown to be equivalent.

Still, not only the apparent abstrusity of Hamilton’s work added to his name sinking into oblivion, it was enhanced by the fact that his mathematical-physical-astronomical legacy combined two aspects, each of which by itself overshadowed the general view on his work. One is that he was a generalist, almost to the extreme, which means that he hardly gave examples for his readers to work with and to learn from. The other, that he made his discoveries in what during a large part of the twentieth century were separate fields of science, which means that people tended to choose the discovery in their own discipline as the most important one, and his work was hardly judged in its entirety. That was already noticed in 1866, a year after Hamilton’s death, when **Charles Pritchard*** wrote in his **éloge**, “It is as yet premature to anticipate on which of his investigations or discoveries Hamilton’s fame will ultimately rest. There are mathematicians among us who in this respect would be inclined to name his Calculus of Quaternions; others would say that none of his writings can overshadow the importance of his Dynamical Theorems.”

* Hamilton’s eldest son William Edwin attended Pritchard’s London grammar school for a year, but he did not **like it very much**.

Despite the revaluation of his work, and its growing influence, as shown below, it appears that also restoring the view on his private life is necessary to achieve the restoration of his general reputation as one of the great scientists. I certainly hope that I made a case strong enough for such a restoration, having written about Hamilton’s “happy and studious” private life, therewith showing him as he described himself, “a labour-loving and truth-loving man.”

Because Hamilton’s work is not discussed further on this website, an overview of its modern use is given here. Hamilton is widely seen as one of the greatest scientists of his time; where one of his major discoveries would have been enough to make him famous, Hamilton made two. And because he was a **generalist** pur sang, nowadays both discoveries appear in many branches of science, “building bridges”^{(1)} in physics and “weaving together”^{(2)} advances in mathematics. Hamilton believed that his work was “for a future age entirely” but he would have been very surprised to see what that future age looks like; that his quaternions are now used in apparatuses he could not have dreamt of, and that his mechanics is now used to describe both particles and the Universe, spaces he never could have dreamt up.

*The good of H is not in what he has done but in the work (not nearly half done) which he makes other people do. But to understand him you should look him up, and go through all kinds of sciences, then you go back to him, and he tells you a wrinkle.*

**— James Clerk Maxwell**

In 1871 to his friend **Peter Guthrie Tait**, in connection to Tait’s **application** of Hamilton’s **varying action** to **brachistochrones**.

As given on the plaque at **Dunsink Observatory**

and the one at **Broom Bridge**

*A call for information**
*

*
I would like to add more disciplines in which Hamilton’s work is used, such as robotics, structural biology, biomechanics, chemistry, data security. If anyone using Hamilton’s work, including variations and extensions of it, from bi-quaternions to geometric algebra, could provide me with a short overview like the ones below I would happily add it.*

**Optics**

Hamilton’s first discovery was a new way to describe optics. He entered College on 7 July 1823, seventeen years old, and on 13 December 1824 his paper ‘**On Caustics**, part I’, was read at the meeting of the Royal Irish Academy. It was communicated by **Brinkley**, then Royal Astronomer and president of the RIA. The paper was **not accepted** for publication in the Transactions and referred to a committee. On 13 June 1825 the comittee **reported**
that it was so abstract and general that it was necessary to explain how the formulae and conclusions were obtained. The paper then evolved into Hamilton’s first paper on the **Theory of Systems of Rays**, which was published in the Transactions in 1828. It is noted there that the paper was read (1)3 December 1824,* acknowledging that it was in fact the same paper, and in a footnote Hamilton comments that he had extended it during the periods of delay of printing the volume.** Three Supplements would follow, the
**Third Supplement** in 1832. It contains the prediction of conical refraction for which he would be knighted.

* The meetings were on Monday; 3 December was a printing error.

** The footnote was written at the Observatory in June 1827; Hamilton was **appointed** Royal Astronomer on 16 June 1827, passed his final exams on 19 and 20 June, and received his BA on 10 July. He therefore must have written the footnote while staying with the departing Brinkley at Dunsink Observatory.

**Geometrical optics and conical refraction**

Mike Jeffrey writes, “In 1832 Hamilton used mathematics, that strange abstract language of symbols and axioms, to predict something truly absurd, and obviously physical nonsense. Hamilton predicted a singularity, a point where light's deterministic journey through a simple crystal broke down. In one stroke, the field of singular optics was born and a sensation began that would take 173 years to run its course. Despite prompt **experimental confirmation** of Hamilton's beautiful mathematical theory, the phenomenon was long hindered by controversy and misconception. Victorian mathematics contained only the initial sparks of the asymptotic techniques which would be needed to achieve a full understanding. Conical refraction entered amidst a climax in the contest between undulatory and corpuscular theories of light, entwined in the earliest roots of wave asymptotics and singular optics. The modern theory of light has its origins in Christian Huygens’ 1677 wave theory. This theory did not explain diffraction and did not account for polarisation, which favoured the corpuscular theories backed by the intellectual might of Pierre-Simon Laplace and Isaac Newton. Augustin Fresnel reversed this dominance in 1816 when he discovered the wave theories of refraction and diffraction. Describing light rays as the normals to level surfaces of some characteristic function, Hamilton’s formulation of geometrical optics married the wave theory of Fresnel with the ray method of Newton. Hamilton’s prediction continues to stretch the capability of lasers and computers of the modern age, and embodies all of the complexities of multiple-scales and singularities that plague modern science.”^{(3)}

That “even this esoteric piece of Hamilton’s work is continuing to be made use of” is shown for instance in articles about **Conical Refraction in Biaxial Crystals** and ** Conical Refraction Optical Tweezers**.

**Hamiltonian mechanics**

In 1833 Hamilton **wrote** about his work: “I am still engaged [...] on a work which has already occupied me since I was about eighteen, in attempting, with the help of the differential or **fluxional calculus**, to remould the geometry of light by establishing one uniform method for the solution of all the problems deduced from the contemplation of one central or characteristic relation.” In **Spring 1833** Hamilton “extended from Optics to Dynamics his algebraic method of a characteristic function.” In **1834** and **1835** he further developed his theory, leading to his **Second Essay on a General Method in Dynamics**, received 29 October 1834, read 15 January 1835. Instead of describing mechanics by the working of forces, as Newton did, Hamilton used the energies of the systems under scrutiny. This **mathematically elegant** reformulation of classical mechanics is now called Hamiltonian mechanics and, roughly speaking, the energy of a system is called the Hamiltonian.

**The Hamiltonian**

Terence Tao writes, “At first glance, the many theories and equations of modern physics exhibit a bewildering diversity: compare for instance classical mechanics to quantum mechanics, non-relativistic physics to relativistic physics, or particle physics to statistical mechanics. However, there are strong unifying themes connecting all of these theories. One of these is the remarkable fact that in all of these theories, the evolution of a physical system over time (as well as the steady states of that system) is largely controlled by a single object, the Hamiltonian of that system, which can often be interpreted as describing the total energy of any given state in that system. Roughly speaking, each physical phenomenon (e.g. electromagnetism, atomic bonding, particles in a potential well, etc.) may correspond to a single Hamiltonian *H*, while each type of mechanics (classical, quantum, statistical, etc.) corresponds to a different way of using that Hamiltonian to describe a physical system. [... In mathematics,] the Hamiltonians play a major role in dynamical systems, differential equations, Lie group theory, and symplectic geometry. [...] Because of their ubiquitious presence in many areas of physics and mathematics, Hamiltonians are useful for building bridges between seemingly unrelated fields, for instance in connecting classical mechanics to quantum mechanics, or between symplectic mechanics and operator algebras.”^{(1)}

**Hamiltonian mechanics in mathematics: symplectic geometry**

Fabian Ziltener writes, “One of the examples of the use of Hamiltonian mechanics in mathematics is symplectic geometry. This is the theory of symplectic structures on manifolds, spaces that locally look like the space we live in but may have any dimension. Describing the state of a classical mechanical system by its generalized position q and generalized momentum p, phase space consists of all such pairs (q,p). In Hamilton’s formalism the motion of a classical mechanical system is governed by Hamilton’s equation, a first order ordinary differential equation for a point in phase space as a function of time. Symplectic geometry has its roots in this reformulation of classical mechanics; in Hamilton’s equation of motion, which is equivalent to Newton’s equations of motion, the standard symplectic structure occurs. Informally, a symplectic structure on a smooth manifold is an assignment that yields a real number for every 2-dimensional subset that is contained in the manifold. Symplectic geometry studies local and global properties of symplectic structures and Hamiltonian systems. A famous conjecture by Vladimir Arnold states that under certain conditions periodic solutions of Hamilton’s equation exist. Physically, such a solution corresponds to a mechanical system that returns to its initial point in phase space after a fixed time.”^{(4)}

**Port-Hamiltonian systems in complex physical systems modeling**

Arjan van der Schaft writes, “Hamilton and Lagrange showed that the dynamics of any mechanical system, in the absence of energy dissipation and without interaction with its surroundings, can be formulated as a set of Hamiltonian differential equations. These equations are determined by the Hamiltonian function (total energy) and the symplectic structure on the phase space of the system. Inclusion of energy-dissipating effects (such as damping) and interaction with other systems, results in what is nowadays called a ** port-Hamiltonian** system. ‘Port’ refers to the interconnection channels of the system, similar to the use of the word in electrical circuit theory. Interconnections of simple port-Hamiltonian systems lead to more complex ones. The Hamiltonian of the complex system is the sum of the subsystem Hamiltonians, while its geometric structure is derived from those of its subsystems. This results in a general mathematical framework for the modeling, analysis and control of complex multiphysics systems, as occurring abundantly in the exact and engineering sciences.”

**Quaternions**

Hamilton’s second discovery was the extension of the imaginary numbers in such a way that rotations in three dimensions could be described. Because they appeared to have four components instead of three as was expected, Hamilton called them quaternions.* He developed them as pure mathematics, but at the same time he aimed, and succeeded, to use them to solve physics, engineering and astronomical problems.** The quaternions had a difficult start, because they ended commutativity in algebra which was not easily accepted.

Fiacre Ó Cairbre writes, “The mathematical world was shocked at his audacity in creating a system of “numbers” that did not satisfy the usual commutative rule for multiplication. Hamilton has been called the “Liberator of Algebra” because his quaternions smashed the previously accepted convention that a useful algebraic number system should satisfy the rules of ordinary numbers in arithmetic. His quaternions opened up a whole new mathematical landscape in which mathematicians were now free to conceive new algebraic number systems that were not shackled by the rules of ordinary numbers in arithmetic. Hence, we may say that Modern Algebra was born on October 16, 1843 on the banks of the Royal Canal in Dublin.”^{(6)}

But Hamilton’s work was also regularly regarded with disbelief; in 1853 he **wrote to a friend**, “You will I hope bear with me if I say, that it required a certain capital of scientific reputation, amassed in former years, to make it other than dangerously imprudent to hazard the publication of [the Lectures in Quaternions] which has, although at bottom quite conservative, a highly revolutionary air. It was a part of the ordeal through which I had to pass, an episode in the battle of life, to know that even candid and friendly people secretly, or, as it might happen, openly, censured or ridiculed me, for what appeared to them my monstrous innovations.” Another problem was that quaternions live in four dimensions and therefore are hardly visualisable. Hamilton died believing that the quaternions would be at the heart of physics, but about twenty years after his death vector analysis was developed, and because contrary to quaternions vector analysis was very visual, intuitive and easy to work with, in physics the quaternions themselves disappeared for a long time. Only in 1967 vector analysis and the quaternions were **reconnected** again.

Michael Crowe writes, “Josiah Willard Gibbs [in] his **Elements of Vector Analysis** [...] presents what is essentially the modern system of vector analysis.” In 1888 Gibbs wrote to Victor Schlegel that reading Maxwell’s **Treatise on Electricity and Magnetism**, he concluded that ““although the methods were called quaternionic, the idea of the quaternion was quite foreign to the subject. I saw that there were two important functions (or products) called the vector part & the scalar part of the product, but that the union of the two to form what was called the (whole) product did not advance the theory as an instrument of geom. investigation.” Gibbs then “began to work out ab initio” a new form of vector analysis that involved two distinct products as well as various other features of modern vector analysis. [...] “I saw that the methods wh. I was using, while nearly those of Hamilton, were almost exactly those of
**Grassmann**.” Gibbs [...] adds: “I am not however conscious that Grassmann’s writings exerted any particular influence on my VA, although I was glad enough in the introductory paragraph to shelter myself behind one or two distinguished names....””^{(7)}

Because therefore vector analysis directly ‘emerged’ from the quaternions it can easily be claimed that, in the form of vectors, the quaternions are at the heart of physics, just as Hamilton had expected. He had an open mind, and doubtlessly would have welcomed this ‘spin-off’ from his quaternions, in which the word ‘vector’ was used in the sense he had given it, and the word ‘scalar’ as he had coined it.

* The nowadays ‘well-known’ story that Hamilton searched for the quaternions for years on end, and the resulting suggestion that his children asked him about it for years, is not true, and actually, no one even claimed that; it is again a gossipy addition to the sad and alcoholic picture of a distressed Hamilton. In his 1967 *A History of Vector Analysis* Michael Crowe does not mention how long the children asked about the quaternions, and Hankins writes in his 1980 biography that Hamilton searched “off and on for the elusive triplets.”

In a **letter** Hamilton wrote just a month before his death to his son Archibald, he described how he came to his discovery. “I happen to be able to put the finger of memory upon the year and month - October, 1843 - when having recently returned from visits to Cork and Parsonstown, connected with a Meeting of the British Association, the desire to discover the laws of the multiplication referred to regained with me a certain strength and earnestness, which had for years been dormant, but was then on the point of being gratified, and was occasionally talked of with you. Every morning in the early part of the above-cited month, on my coming down to breakfast, your (then) little brother William Edwin, and yourself, used to ask me, “Well, Papa, can you *multiply* triplets”? Whereto I was always obliged to reply, with a sad shake of the head: “No, I can only *add* and subtract them.””

The ‘desire’ thus had ‘for years been dormant,’ and Hamilton had travelled to attend meetings until mid-September. From Hamilton’ remark it can be seen that the children asked at breakfast how it went during the first two weeks of October; Hamilton may have started this search late in September. It therefore took him two or at the most three weeks, from late September or the beginning of October until the day of discovery, 16 October.

** Physics as we now know it did not exist yet, see below for the **state of science in Hamilton’s days**. Yet as he had intended, next to the well-known applications such as the orbits of planets, Hamilton also used them to solve **engineering problems**. Graves writes, describing 1850, “it appears from existing letters that Hamilton was applied to by civil engineers, engaged upon Irish railways, to give the aid of his mathematical knowledge in solving a problem of some practical interest connected with the construction of oblique, or skew, bridges. Hamilton applied to it his method of quaternions, and on the next day supplied the inquirers with an exact solution. A note from Professor Downing, of the Trinity College School of Engineering, returns his sincere thanks to Sir W. Hamilton for his demonstration of that proposition hitherto only approximately solved.“'

**Quaternions in space travel**

For the quaternions the coming of computers changed everything. In the late 1950s the quaternions re-emerged, apparently at first in **aircraft simulation**, because computers appeared to work with quaternions more easily than with vector analysis and matrix calculus, therewith using less computing power.* After having been used in the **Space Shuttle program**,** their use in space travel became very widespread.

Noel Hughes writes, “Vectors and quaternions, along with algebra, trigonometry, geometry, etc. are an intertwined set of tools which can be used to solve many problems that can appear intractable. [Quaternions are used in] spacecraft guidance, navigation and control engineering. [...] Prior to the dawn of the space age and the need for attitude description that does not have singularities, ambiguities, etc., [for most people] quaternions were little more than an esoteric mathematical oddity. [Nowadays] quaternions are used extensively in the Aerospace industry, in the animated film industry and, to a lesser extent, in the medical world. [...] The fundamentals are simple, elegant and straight forward once the superfluous stuff is stripped away.”^{(8)}

**SPICE**, an ‘Observation Geometry System for Space Science Missions,’ is completely **based** on quaternions.

Charles Acton writes, “The first “official” use of SPICE was on the Magellan mission, launched in 1989, and it has been used on nearly every worldwide planetary mission since then. For “modern” missions, i.e. everything since Magellan, SPICE is used throughout the mission life-cycle, starting from mission formulation in what NASA calls “Phase A”, through operations (“Phase E”), then in post-mission (“Phase F”) data analysis, and then even for many years thereafter.”^{(9)}

Joe Zender writes, “Today, for nearly all spacecraft that are sent out into our solar system their attitude is available in quaternions. They are publicly available and distributed by **NASA's NAIF Facility**. Also most landers’ and rovers’ positional information can be found there. The data covers missions from NASA, The European Space Agency (ESA), The Japanese Space Agency (JAXA), The Russian Space Programme (ROSCOSMOS) and other Agencies. Users are scientists and engineers using software libraries that allows a “rather easy” computation of derived geometric information. One can compute e.g. the answer to the following questions: “At what time will the Mars Express spacecraft come into the field-of-view of the antenna of the Mars Exploration Rover?”, or “Will CASSINI fly through a cometary debris field in year X?”^{(10)}

* Alfred C. Robinson writes in his **1958 article**, “The general subject of quaternions as applied to coordinate conversions has been under investigation for approximately two years, though the bulk of the work reported here was accomplished during the last six months of 1957.” And in his abstract, “It is shown that the quaternion method is no more sensitive to multiplier errors than is the direction cosine method, and it requires nearly 30 per cent less computing equipment. [...] By every important criterion, the quaternion method is no worse than, and in most cases, better than the direction cosine method.”

**Quaternions in animation**

In 1985 the apparently earliest article introducing quaternions to computer graphics was published.

Ken Shoemake writes, “Solid bodies roll and tumble through space. In computer animation, so do cameras. The rotations of these objects are best described using a four coordinate system, quaternions, as is shown in this paper.”^{(11)}

Thereafter the quaternions in this field have been developed almost beyond recognition.

Manos Kamarianakis and George Papagiannakis write in their 2020 article, “Skinned model animation has become an increasingly important research area of Computer Graphics, especially due to the huge technological advancements in the field of Virtual Reality and computer games. The original animation techniques, based on matrices for translation, rotation and dilation, are still applied as the latest GPUs allow for fast parallel matrix operations. The fact that the interpolation result of two rotation matrices does not result in a rotation matrix, forced the use of quaternions as an intermediate step. The extra transmutation steps from matrix to quaternions and vice versa, adds some extra performance to the animation but yields better results, solving problems such as the gimbal lock. Nowadays, the state-of-the-art methods for skinned model animation use dual-quaternions, an algebraic extension of quaternions. [...] Dual-quaternions handle both rotations and translations, but cannot handle dilations. [...] **Conformal Geometric Algebra (CGA)** is an algebraic extension of dual-quaternions, where all entities such as vertices, spheres, planes as well as rotations, translations and dilation are uniformly expressed as multivectors. The usage of multivectors allows model animation without the need to constantly transmute between matrices and (dual) quaternions, enabling dilation to be properly applied with translation.”^{(12)}

**Quaternion algebras**

Yet for mathematics the history of quaternions is quite different; there they never disappeared from sight.

John Voight writes, “Quaternion algebras have threaded mathematical history through to the present day, weaving together advances in [many branches of mathematics, and they ...] continue to arise in unexpected ways. [...] Quaternion algebras sit prominently at the intersection of many mathematical subjects. They capture essential features of noncommutative ring theory, number theory, K-theory, group theory, geometric topology, Lie theory, functions of a complex variable, spectral theory of Riemannian manifolds, arithmetic geometry, representation theory, the Langlands program – and the list goes on. Quaternion algebras are especially fruitful to study because they often reflect some of the general aspects of these subjects, while at the same time they remain amenable to concrete argumentation. Moreover, quaternions often encapsulate unique features that are absent from the general theory (even as they provide motivation for it). [...] The enduring role of quaternion algebras as a catalyst for a vast range of mathematical research promises rewards for many years to come.”^{(2)}

For how the efforts of very many people turned Hamilton’s discovery into the contemporary quaternion algebras, see the first chapter of Voight’s ** Quaternion Algebras**.

**Astronomy**

A special place is for astronomy because it pervaded all Hamilton’s work. In 1827, when Hamilton was still very young, he **described** his passion for mathematics to William Wordsworth (1770-1850), showing how it was always entwined with his love for astronomy and his deep religious feelings. “Science, as well as Poetry, has its own enthusiasm, and holds its own communion with the sublimity and beauty of the Universe. And in devoting myself to its pursuits, I seem to myself to listen [...] to the promise of a [pure and noble] reward, in that inward and tranquil delight which cannot but attend a life occupied in the study of Truth and of Nature, and in unfolding to myself and to other men the external works of God, and the magnificent simplicity of Creation.”

Hamilton indeed always related his work to Nature and the Universe. To give some examples; in 1833, having extended his mathematical methods from optics to dynamics, he wrote to his friend Aubrey de Vere that he had been drawing up, for the *Dublin University Review* a sketch of his ‘general method for the **paths of light and of the planets**’; in 1848 he discussed his **optics** with Lord Rosse, who had built the then largest telescope in the world. He **applied** his Calculus of Quaternions to the **theory of the Moon**, and in both books, the ** Lectures (1853)** and

**Astrophysics**

Andrew Hamilton (no relation to Sir WRH) writes, “Astrophysicists, who harness mathematics and physics to study astronomical phenomena, use Hamilton's work every day all the time. Hamiltonians are at the core of the two pillars of modern physics, general relativity and quantum field theory. Hamiltonian dynamics is central for understanding the dynamics of gravitating systems such as solar systems and galaxies, or the dynamics of electrodynamic systems such as plasmas. Hamilton's quaternions are by far the most powerful and elegant way to understand and encode spatial rotations, and his biquaternions, having complex numbers as their coefficients, do the same thing for spacetime rotations, also called Lorentz transformations. Hamilton's impact on theoretical astrophysics is everywhere.”^{(13)}

^{(1)} **Terence Tao** (2008), **Hamiltonians**.

^{(2)} **John Voight** (2020), ** Quaternion algebras**.

In 2017 I published (a corrected version of) my first book, or actually a history essay because it is written as a ‘defense,’ ** A Victorian Marriage : Sir William Rowan Hamilton**, in which I showed that the unhappy and alcoholic view on Hamilton is flawed, and how this idea emerged, unintentionally, from the enormous biography about Hamilton, written by

The **first seven chapters**, **Introduction**, **Early years**, **A lover**, **A brother**, **A husband**, **A good marriage**, and **Later years**, are a description of Hamilton’s private life. In 1824, only nineteen years old, Hamilton fell in love with Catherine Disney. After some months of unspoken love she married someone else, and it took him six years to cope with his loss. In 1831 he fell in love with Ellen de Vere, who did not love him back, causing months of very melancholy feelings. Then, in the summer of 1832, Hamilton made a remarkable discovery; he saw that he was wasting his life on passion, and found a way to change his behaviour. His zest for life was restored, and he fell in love with Helen Bayly.

Indeed, contrarily to what has been suggested, that Hamilton always remained to love only Catherine and hence had an unhappy marriage, it is clear from a letter to a friend that he really had been in love with Ellen de Vere, writing that he had had “another affliction of the same kind and indeed of the same degree” as his love for Catherine had been. And having sent his ante-nuptial poems about Helen Bayly to **Coleridge**, believing that poems had to come from true feelings and highly admiring Coleridge, may serve as one of the ‘proofs’, if these are needed, that he indeed was very much in love with her. The chapters end with Hamilton’s later years and death.

**Chapter 8**, **A lost love**, is about what happened with his first and lost love **Catherine Disney**. It is shown that at the time of her marriage, in 1825, Hamilton had not known that Catherine had been forced to marry someone she did not love. Having been told that she was going to marry he had not seen her again; he saw her only in 1830, 1845, and in 1853 shortly before she died. Hamilton had assumed that Catherine had wanted to marry until, in 1830, he visited her, and saw that she was unhappy. About the 1845 visit nothing further is known, but in 1848 she told him in a correspondence that her marriage had been unhappy from the start. Only in 1853, some weeks before her death, she could finally tell him that she was coerced into this marriage, and that she had wanted to marry him. Each time Hamilton again learned about new details, and about how terribly unhappy Catherine was, he was understandably distressed. Which is entirely different from having loved only her his whole life.

The **9th chapter**, **Solemn dogged seriousness**, is a description of the Hamiltons at home, as far as it could be extracted from the biography; although they had their ups and downs, as everyone has, they had a good and happy marriage. Familiar traits are discussed, and anecdotes given, as told by the eldest son, William Edwin, after his father’s death. One of these anecdotes became the direct origin of a part of the **contemporary gossip**; the view on Hamilton as a very disorderly man, which led to the conclusion that Lady Hamilton thus was a bad housewife, from which it was concluded that their marriage was unhappy, and that Hamilton started to drink alcohol because she did not serve dinner. Which clearly was not the case, as could already have been concluded from the anecdote itself. This chapter also contains a discussion of their illnesses, Hamilton’s gout and Lady Hamilton’s weak health. Very likely reasons are given for Lady Hamilton’s two nervous breakdowns, which directly had to do with her marriage; being a married woman in Victorian times was indeed extremely difficult. Yet both times the Hamiltons were able to solve their problems.

The **10th chapter**, **An occasional mastery**, is about Hamilton’s alleged alcoholism. It is discussed what exactly happened, and that what Graves called “an occasional mastery”, hinting at it long before describing it while vaguely predicting doom to come, was a one-time event in 1846. It is also discussed how especially in Hamilton’s so-called ‘High Church days,’ which lasted from about 1839 until late in 1845 or very early in 1846, it was extremely unlikely that he was drinking too much. And indeed, Graves never claimed that Hamilton was an alcoholic.

In the first part of the **11th and last chapter**, **By no means an alcoholic**, Hamilton’s **use of alcohol** is **discussed** based on the **DSM-5**, using the information found in Graves’ biography. The conclusion was that Hamilton did not meet the DSM-5 conditions for alcoholism and that, had he lived now, he thus would **not be regarded as alcoholic**.

Having shown that Hamilton was not an alcoholic, it was considered how much risk there had been that he would have become one. To that aim the data from Graves’ biography about when and how much alcohol Hamilton drank are used, in a worst case scenario, to fill in the **AUDIT** test which can be found on p. 17 of the **manual** published by the World Health Organization. It is designed to test what the risks are for someone, **in this case Hamilton**, to become an alcoholic. The **overall conclusion** was that, in this worst case scenario, during two periods of his life Hamilton would have had an increasing risk of becoming alcoholic, but that he never reached the higher risk levels of becoming one.

During these two periods of increasing risk Hamilton, who always remained temperate at home, sometimes drank much in public. The first period started in 1844 when after having discovered the quaternions Hamilton seemed to become overworked, and ended in 1846, with the **event at the Geological Society**. Thereafter Hamilton was warned by Charles Graves, brother of the biographer Graves and fellow mathematician at Trinity College Dublin, that he was ruining his Dublin reputation; Hamilton immediately changed his behaviour and became abstemious for two years. The second period **started in the summer of 1848** and ended when, **most likely in 1851**, but in any case before the end of 1853, Hamilton was again warned by Charles Graves. Drinking wine, and sometimes much, at dinners and parties had been completely accepted until around 1840 the Temperance Movement had reached Dublin, and apparently the gossip about Hamilton’s drinking was worsening again. This second time he changed his behaviour less rigorously but lasting; although he did not abstain again, he never drank much any more.

It then is discussed briefly where Graves’ information about Hamilton’s private life came from; Graves lived in England from 1833 until 1864, thus from the time Hamilton married until one year before he died. Apart from writing letters other means of contact did not exist yet, and they did not visit each other frequently, apparently not even yearly, which means that Graves hardly saw Hamilton live his daily life. The essay is concluded by a revaluation of the two main biographies, written by Graves in the 1880s and by Thomas Hankins in 1980. It is shown that all the information these two biographies contain can be placed in a much more positive light than is done nowadays, by putting Hamilton’s life in the context of his time, and carefully noticing all the nuances Graves gave in his biography.