[Monthly Notices of the Royal Astronomical Society 26 (1866), 109-118.]

WILLIAM ROWAN HAMILTON, one of the ablest mathematicians that this or any other country has produced, and for nearly forty years a Fellow of the Royal Astronomical Society, was born in Dominick Street, Dublin, in the year 1805. His father was by profession an attorney, and was long held in great estimation both for his personal character and his professional ability. The branch of the Hamilton family from which he was descended, originally settled in the north of Ireland, in the reign of James the First; and it is said that by right a baronetcy belonged to the representative of this branch, a near relative of his own; although the claim could not be fully supported, owing to merely technical flaws. Thus Hamilton may have been in some degree indebted for his great and versatile mental capacity to a mixture of race.

William Hamilton is one of those rare instances, where the
promise of early childish precocity has not been disappointed by
the attenuated achievements of riper years. At various stages of
his boyhood, not to say childhood, for the precocity manifested
itself at the early age of *four*, he is said to have
successively acquired some notable acquaintance with no less than
thirteen languages, European and Asiatic. His attention was
directed to the latter, because it was originally hoped that,
enjoying as he did the opportunity of good patronage, his career
would be passed in India. It is recorded on evidence which
deserves respect, that at the age of seven he was examined in
Hebrew by a fellow of Trinity College, Dublin, and that ``the
child passed a better examination in that language than many
candidates for the fellowship.'' For obvious reasons we hope
that there is some pardonable though very natural exaggeration in
the statement. It is certain however that the attention of the
Persian Ambassador, when on a visit to Dublin, was attracted by a
letter of greeting written in Persian by young Hamilton at the
age of fourteen. Whether or not any allowance is to be made for
the shadow of the future overlapping the memory of the past, it
is quite certain that the vast intellectual capacities of the boy
were evinced and cultivated at a very early age, and what is of
far greater consequence, this early mental activity did not
prostrate or forestall the successful exertions of maturer life.
It is quite possible that the literary turn thus given to his
earlier pursuits may have happily laid the foundation of the
peculiar combination of metaphysics and poetry, which
distinguished some of his mathematical performances from those of
most other men. For his early training in ancient and modern
languages, he was indebted to the loyal care of his uncle, the
Rev. James Hamilton, curate of Trim; but in science and
mathematics he appears to have been nearly self-taught and
self-directed; in his case, as in that of many other eminent men,
this circumstance probably conduced to the originality of his
maturer conceptions, and to the peculiar style in which he
embodied them.

By the age of fifteen, young Hamilton had mastered the usual course of elementary mathematics, pure and applied; and in some instances had become familiar with works of original research. He appears to have evinced a peculiar taste for long and difficult arithmetical approximations, and to have shown himself no mean antagonist in the solution of numerical puzzles when matched against a certain arithmetical prodigy, who, coming from America, happened at that time to be exhibited in Dublin. By the age of seventeen, he had mastered Newton's Principia, and a year later found him in possession of most of the processes in the Mécanique Céleste. Meanwhile, and notwithstanding this very unusual advancement in mathematical knowledge, the main culture of his mind had been classical: and that, not alone from natural predilection, but on account of the requirements of the collegiate course on which it was his intention to embark and to compete.

It is almost needless to say that young Hamilton, with a mind thus disciplined and furnished, entered upon his course at Trinity College, Dublin, if not without able competitors, at all events without an equal, whether in literature or mathematics. As might be expected, he carried all before him; and when we speak of success in his literary efforts, it must be understood that we include Poetry in the list, inasmuch as on two successive occasions he gained the Vice-Chancellor's Prize for English verse. It is to this early and successful cultivation of the lighter elegancies of scholarship that his friends were indebted for a vein of poetical thought and expression which graced alike his correspondence and his conversation, and which is sometimes observable even in his graver compositions.

It appears that in the year 1822, one year before his entrance at the University, young Hamilton, now in his eighteenth year, attracted the notice of the celebrated Dr. Brinkley by certain objections which he made to a demonstration propounded by Laplace in the Mécanique Céleste. On being invited to pay a visit to that well-known astronomer, the young student thought that he should most properly express his feelings of respect by carrying in his hands another instance of independent research on the osculation of certain curves of double curvature. This introduction of Hamilton to the veteran professor laid the foundation of a mutual friendship and respect which continued to increase during Dr. Brinkley's tenure of office.

In the first year of his student life at Dublin, Hamilton,
notwithstanding his close attention to the elementary line of
study necessarily prescribed to under-graduates, nevertheless
engaged himself in a line of original research. Even before his
entrance at the University he had directed his thoughts to the
difficult subject of Caustics, and having now completed the
memoir, it was read before the Royal Irish Academy in 1824. This
paper was referred as usual to the consideration of a committee
of scientific men, who, being struck with the originality of the
conception, and the evidences of analytical power which it
contained, recommended the author to give those further
developments of the subject which evidently lay within his grasp.
The result of this encouragement to the young philosopher was the
speedy completion of a memoir which may be said to contain the
germ of a large portion of the noble work which it was his lot to
contribute towards the advancement of physical knowledge.
Instead of an essay on Caustics, his paper was now enlarged into
a wider and more general investigation, under the title of a
``Theory of Systems of Rays.'' It may be no exaggeration to say
of this memoir, in conjunction with its subsequent supplements,
that it is one of the ablest contributions ever made to our
knowledge of the geometry of optics. Chasles, one of the most
distinguished of modern geometers, speaks of it as
``*dominant toute cette vaste théorie*.'' Starting from
the simple fundamental principle that light, whatever may be its
cause or its constitution, is amenable to what mathematicians
call ``The Principle of Least Action,'' or, in other words,
probably as true, and certainly more expressive, amenable to the
*principle of no waste in nature*, Hamilton, in a train of
analytical logic unimpeachable, and with a mastery over the
management of algebraic symbols probably never surpassed, shows
that the theory of a system of rays reflected or refracted any
number of times at given surfaces, depends on the determination
of a single principal function V, which contains in
itself all the properties of the system of rays, in a manner
analogous to that in which the properties of a curve are
contained in its equation. The same theory is, in the
supplements, extended to the more complicated and recondite
question of double refraction in biaxal crystals, and at length
lands the reader in one of the most remarkable scientific
predictions contained in the records of physical inquiry. But of
this prediction we must speak presently.

When the first part of this ``Theory of Systems of Rays'' was presented in April 1827 to the Royal Irish Academy, it will be remembered that Hamilton was as yet an undergraduate of twenty-one years of age. In this year the Professorship of Astronomy in Trinity College, Dublin, became vacant by the promotion of Dr. Brinkley to the bishopric of Cloyne. Such was his deserved reputation, that, not withstanding the appearance of other and most formidable candidates in the field, and although, moreover, he had as yet taken no academical degree, Hamilton was elected to the vacant chair.

This circumstance is of itself sufficiently remarkable, and reflects equal honour upon the authorities who ventured to make the appointment, and on the young geometer who, by dint of genius and laborious study, was qualified to discharge the duties of the post. In connexion with this arrangement there is a point of osculation with our own Society of sufficient interest to demand our notice. The present Astronomer Royal, at that time Lucasian Professor of Mathematics in the University of Cambridge, was one of the candidates for the vacant post at Dublin; and he too, like Hamilton, had been advanced to his professorship before he had ceased nominally to be in pupilage. We are not here, even by the remotest implication, suggesting a comparison between these eminent men; such a comparison would not only be utterly unfitting, but, owing to the divergence of the lines of research adopted by the two Geometers, would be wholly impossible. Nevertheless the thought unavoidably presents itself, that for both parties, and for the general interests of science, the decision of the Dublin electors was a happy one. Had it been otherwise, the one, in all probability, from certain natural tendencies of his mind, would have become a clergyman - no doubt a most eminent one - in the Irish Church; while Greenwich and our own Society might have lost the other.

``There is a Divinity which shapes our ends,

Rough-hew them how we will.''

In 1828 Hamilton became a Fellow of the Royal Astronomical
Society, and thus at the time of his decease was among the
oldest, as his name was certainly among the most honoured of our
members. In 1833 he made known, in one of several supplements to
the ``Theory of Systems of Rays,'' his great discovery of Conical
Refraction. In this memoir, starting again from the principle of
least action, and, as before, conducting the investigation by
means of a single Principal Function, he establishes the entire
theory of double refraction; and, applying it to the case of
biaxal crystals, by a new and simpler
method^{1}
than that originally pursued by Fresnel, he obtains the equation
to the form of wave assumed by the vibrating ether within the
crystal. On examining the form of the wave surface, Hamilton,
with remarkable sagacity, observed that if the theory and the
results were true, a single ray of light incident at a certain
angle on a biaxal crystal, must of necessity pass into it, not as
one ray, nor even as two rays, but as a conical sheet of light,
and then finally emerge as a luminous cylindrical surface. And,
again, his profound and complicated analysis indicated that there
was also a direction within the crystal, such, that if an
internal ray of light passed along it, it would emerge from the
crystal, not as one ray, but as a luminous conical shell. Such
results as these were not only apparently contrary to all analogy
and expectation, but formed, if the experiment could indeed by
made, a species of *experimentum crucis* of the truth of the
undulatory theory of light. Notwithstanding the difficulty of
the case, the experiment was at length successfully performed by
Dr. Humphrey Lloyd, of Dublin, whose patient ingenuity, and faith
in the profound work of the geometer, were rewarded by the sight,
for the first time, of what cannot properly be called less than
the astonishing phenomenon of a single ray spread out, by
refraction in a crystal, into an infinite number of rays, forming
the surface of a luminous cone.

From the sagacity of Hamilton, and of his friend Dr. Lloyd, thus
constraining the little crystal of Arragonite to give up,
Sphinx-like, its secret of ages, our thoughts unavoidably turn to
the parallel case of Adams and Leverrier, who, from a similar
strong faith in the laws of nature and in the logic of geometry,
not only predicted the existence of a planet heretofore unseen
and unexpected, but indicated the precise region of the heavens,
where, as soon as it was looked for, it was actually found. We
do not regard such results as valuable only because they
corroborate our conviction of the existence of certain laws
whereon we believe the universe to have been constructed by the
Author of Nature, but still more so because they serve to
encourage the student to persevere in his researches, animated by
the fullest conviction that if truthfully conducted they can only
land him in truth, and leaving the *cui bono* to be
determined by the appreciations, or the wants, or the
curiosities, of men in time to come.

The Royal Irish Academy took cognisance of Hamilton's great
discovery, and of the profound mathematical skill whereby it was
evolved, by conferring upon him their Cuninghame medal; and the
Royal Society awarded him a similar mark of their appreciation of
his merits. In 1837 he was elected President of the Royal Irish
Academy, succeeding^{2}
his friend and early patron, Dr. Brinkley, in the chair, as he
had succeeded him in the Professorship of Astronomy. He retained
this distinguished office for eight years, and on his resignation
he received the thanks of that eminent Academy ``for his high
and impartial bearing in the chair.''

In 1834 and 1835 he communicated to the Royal Society two papers
on ``A General Method in Dynamics.'' Here, again, he commenced
with the same fundamental idea, as that which he had already so
successfully adopted in his ``Theory of Systems of Rays,'' and he
showed that the integration of the differential equations of
motion for any system of bodies may be considered as depending on
the determination of a certain Principal Function, which he
defines in several different forms, but in each case by means of
*two* partial differential equations involving, one of them,
the differential coefficients in regard to the final co-ordinates
(co-ordinates at the time *t*), the other, those in regard to the
initial co-ordinates of the several particles. He also
established in these Memoirs the now well-known
``*Hamiltonian Form*'' of the equations of motion of any
material system.

The two Memoirs just referred to gave occasion to Jacobi's
investigations on ``Partial Differential Equations''
(Crelle, t. xvii. 1837). Jacobi shows that, instead of
``Hamilton's Function'' involving the time and the initial and
final co-ordinates, and satisfying *two* partial
differential equations, it is allowable to consider a function of
the time and the final co-ordinates only, satisfying a
*single* partial differential equation; and he considers
that by omitting to make this simplification, Hamilton presented
his remarkable discovery in at least an imperfect light. There
can be no doubt that the simplification thus introduced by Jacobi
was a most important and valuable one; but it can scarcely be
objected to Hamilton that he failed to perceive all the results
deducible from his own discovery, any more than it can be
objected to Fresnel that he left it to Hamilton to deduce conical
refraction from the very form of the wave surface which Fresnel
was the first to investigate. It must not be forgotten that it
is to Hamilton's discovery as their fountain, though the course
of the stream was directed by Jacobi, that are due all the
developments which have since been made in the vast subject of
Theoretical Dynamics. In a word, it may not be too much to say
that the step in advance made by Hamilton's two memoirs can only
be compared with that effected at an earlier epoch by the
publication of Lagrange's *Mécanique Analytique*. For
this work, also, Hamilton was again awarded a gold medal by the
Royal Society.

We pass over various other characteristic works of this profound
analyst, not because they are devoid of interest or of worth, but
because they are less within the scope of our Society; and we
come at length to what Hamilton considered the crowning labour of
his life, - a labour which for the next twenty years, and indeed
till within a few days of his decease, continued to occupy his
thoughts. The labour here referred to was bestowed on the
invention and the development of the Calculus of Quaternions. In
a memoir such as this, and for the purposes which we have in
view, we must almost despair of explaining, or perhaps of even
conveying an idea of what is the aim and scope of the Calculus of
Quaternions, or in fact what a Quaternion is, and yet without
some such attempt, successful or not, any obituary notice of this
great man would be incomplete. For this purpose, then, we must
bear in mind that in the method of geometry introduced by
Descartes, and which had been retained in astronomical and
physical investigations up to the present time, the position of a
point in space has been determined either by its distances from
three co-ordinate planes, or by what in reality are their
equivalents. Hamilton, however, starts at once by considering
not so much the position of a *point*, as rather the
relation which exists between two *lines* intersecting in
space, having regard both to length and to position. It will
soon be seen that in order to determine these relations
completely, four quantities, or four elements, are necessarily
involved.

1°. There is the relation which the length of the one line bears to the length of the other line;

2°. The angle through which the one line must be conceived to be turned in order that it may coincide with the direction of the other;

3°. The plane in which the two lines lie.

An inasmuch as the determination of this plane involves two
elements, viz., 1°. its inclination to some fixed or
known plane, and 2°. an element which is analogous to the
longitude of a planet's node, it follows that
four^{3}
elements or symbols are required to determine the relation which
one line in space bears to another
line.^{4}
The combination of these four elements, then, forms the
Quaternion of Sir William Hamilton; and as handled and developed
by him, these combinations unquestionably form a calculus of
amazing generality, grasp, and power. As an engine of
investigation, in the general problem of combined rotations, the
method of Quaternions probably has no rival in completeness or in
facility. They remind one of the tentacles of some gigantic
polype, ramifying out into immensity, and bringing back with them
the spoils of space.^{5}

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*. As yet, however, the former
Calculus can hardly be said to be fully developed, or to have
been extensively applied by other philosophers to new lines of
investigation; nevertheless, it can scarcely be supposed that the
persistent and conscientious labour of such a man for twenty-two
successive years can fail to be full of the seeds of thought, and
one day be found to admit and to invite important applications.
It must however be conceded that (partly perhaps on account of
its comparative novelty, and partly on account of the
metaphysical atmosphere which surrounds it), the method is
neither easy nor attractive to any but the ablest and more daring
of the analysts among us; many a man who has essayed to bend this
bow has probably said to himself what Antinous said to his boon
companions:-

``Thou was not born to bend

The unpliant bow, or to direct the shaft.''^{6}

We have just spoken of the metaphysical atmosphere which seems to pervade Hamilton's Calculus of Quaternions; and herein there is little to excite our surprise, for it was natural for a man possessed of a mind so versatile and so profound, to turn it inwards on itself; hence he delighted in metaphysics. But it was not alone because the culture and bias of his mind unavoidably led him in this direction, that many of his mathematical investigations assumed a metaphysical turn, but because he, in conjunction with other thoughtful philosophers, believed that no further great advance in mathematical science was now to be expected, excepting from the metaphysical point of view. Probably it is either a conscious conviction, or an intuitive perception of this, which influences the peculiar phase observable in the mathematical investigations of some of our greatest analysts of the present day.

Hamilton was not only a great mathematician, but by nature he was
also a poet. He was heard to say, ``I *live* by
mathematics, but I *am* a poet.'' If, by this aphorism, he
meant that, had he so chosen, he would have become more eminent
as a poet than he is as an analyst, bystanders might hesitate to
give their assent. Few men, perhaps, are fully conscious of the
ruling bias and the strong points of their own minds. We know
one of our greatest living philosophers who would perhaps say,
``By filial duty I am an astronomer, but I was born a chemist.''
Of another it has been often said, ``He *is* a mathematician
and an observer, but he *was born* an engineer.''
Nevertheless Hamilton was a true poet, and by no means an
indifferent writer of true poetry; and it is quite certain, that
some of our subtlest mathematicians are poets at heart, knowing
it and feeling it. And here it may be worth a passing remark to
mention that Hamilton, in his great Memoir on A General
Method in Dynamics, speaks of Lagrange's Mécanique
Analytique, as a *Poem*. One of our chief living
astronomers hereon remarks: ``Hamilton was right, but he might
have said a poem of most stately rhythm.'' The two works of
Lagrange and Hamilton have points in common.

Hamilton counted among his friends Coleridge, Southey,
Mrs. Hemans, and Wordsworth. It is said, that when the latter,
through Hamilton's enthusiasm, was enabled to get a glimpse of
the inexpressible fascination which surrounds the daring and
*creative* spirit of modern geometry, the old man was for
the first time inclined to admit even a mathematician into the
charmed circle of the brotherhood of poets. The anecdote rests
upon unquestionable authority: nevertheless, we are inclined to
think better things of so great and profound a mind as that of
Wordsworth, and we are convinced that he must, by sheer dint of
sympathy with other minds, have had at least a suspicion of the
fact before the great analyst revealed it. In vindication of the
justice of these remarks on the expansiveness of great
intellects, and on the poetic power which almost invariably is,
at the least, latent within them, we cannot refrain from quoting
the following Sonnet, written by a great Astronomer, on the
occasion of a visit to Ely Cathedral, in company with Sir William
Hamilton:-

Sunday, July29, 1845.The organ's swell was hushed, - but soft and low

An echo more than music rang, - where he,

The doubly-gifted, poured forth wisp'ringly,

High-wrought and rich, his heart's exuberant flow,

Beneath that vast and vaulted canopy.

Plunging anon into the fathomless sea

Of thought, he dived where rarer treasures grow,

Gems of an unsunned warmth, and deeper glow.

Oh! born for either sphere, whose soul can thrill

With all that Pöesy has soft or bright,

Or wield the sceptre of the sage at will,

(That mighty mace^{7}which bursts its way into light),

Soar on as thou wilt, or plunge, - thy ardent mind

Darts on - but cannot leave our love behind.

This memoir would be incomplete if we did not add, that our deceased member, together with the character of a scholar, a poet, a metaphysician, and a great analyst, combined with that of a kind-hearted, simple-minded Christian gentleman; we say the latter because Sir William Hamilton was too sincere a man ever to disguise, though too diffident to obtrude, his profound conviction of the truth of revealed religion. Endued with such qualities as these, what wonder, if of his friends he was almost the idol, and of his university the pride; for he was gentle, and he was eloquent, and he spoke evil of no man, he defended the fair fame of the absent, and he held controversy with none.

Such, then, is an imperfect but unexaggerated sketch of this remarkable man. We will only add, that happily he did not live to survive himself, but in full possession of his faculties, almost in the very presence of the friends who had long admired him; and, what was no new thing to him, supported by the convictions and consolations of his faith, he resigned himself to his rest, as one who knew that he had done a work which had been given him to do.

[C. P.]^{8}

^{1}It
is but a point of justice to state that Mr. Archibald Smith has
subsequently much improved the simplicity of the process by a
very elegant method of elimination.

^{2} Dr. Lloyd,
sen., was President for two years after the death of the
Bishop of Cloyne. Hamilton succeeded Lloyd.

^{3}The
above is in fact one of Hamilton's many illustrations of the
meaning of a quaternion. Analytically speaking, a quaternion is
an expression of the form *w* + *ix* + *jy* + *kz*,
where *i*, *j*, *k*
are imaginary roots of
,
differing from the
imaginaries of ordinary algebra, in that the *order* of
multiplication of these symbols is material, *ij* here not being
= *ji* by = -*ji*, and so for the other symbols.

The geometrical intepretation is this: on taking the usual three
rectangular co-ordinate axes of *x*, *y*, *z*; if
*ij* means
rotate the axis of (*y*) round the axis of (*x*) through
90° of right-handed rotation, then *ji* must mean rotate
the axis of (*x*) round the axis of (*y*) through 90° of
right-handed rotation. Now the result of the former rotation is
a line in the direction of the axis of +*z*; the result of the
latter rotation is a line in the direction of the axis of -*z*:
in this sense then *ij* = - *ji* and so
*jk* = -*kj*, and *ik* = -*ki*.
The symbol (*w*) is the ratio of the lengths of
two intersecting lines (or *vectors*) considered in the
quaternion. Such is a first glimpse of this intricate Calculus.

^{4}Elements
of Quaternions, Longmans, 1866, page 110. This extraordinary
work is the result of the unceasing labours of the two last years
of Sir William Hamilton's life: indeed, it is said to have been
fatally injurious to his health. It was all but finished when
the lamented death of the author arrested its entire completion.
The Board of Trinity College, Dublin, have marked their sense of
the value of this book by defraying the expenses of its
publication.

^{5}With
this simile Sir W. Hamilton expressed his acquiescence to the
writer of this memoir.

^{6}Cowper's translation of the
Odyssey, book xxi.

^{7} The
symbolic analysis of which
the eminent and excellent individual (Sir W. R. H.) supposed to
be addressed has proved himself a most consummate
master. - (Essays by Sir John Herschel.)

^{8}
In
the preparation of this *éloge*, the
writer has received much assistance from Dean Graves, P.R.I.A.;
the Rev. R. P. Graves, of Dublin; and Professors De Morgan and
Cayley.

Links:

- William Rowan Hamilton: Some Nineteenth Century Perspectives
- Sir William Rowan Hamilton (1805-1865)
- History of Mathematics

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School of Mathematics

Trinity College, Dublin