the production of Welsh flannel, and also for the manufacture,
whilst the fashion prevailed, of periwigs of goats, hair.
The title of Baron Abergavenny, in the Neville family, dates
from Edward Neville (d. 1476), who was the youngest son of
the 1st earl of Westmoreland by Joan Beaufort, daughter of
John of Gaunt. He married the heiress of Richard, earl of
Worcester, whose father had inherited the castle and estate of
Abergavenny, and was summoned in 1392 to parliament as Lord
Bergavenny. Edward Neville was summoned to parliament with
this title in 1450. His direct male descendants ended in 1387
in Henry Neville, but a cousin, Edward Neville (d. 1622), was
confirmed in the barony in 1604. From him it has descended
continuously, the title being increased to an earldom in
1784; and in 1876 William Nevill (sic) 5th earl (b. 1826),
an indefatigable and powerful supporter of the conseruative
party, was created 1st marquess of Abergavenny. (See NEVILLE.)
ABERIGH-MACKAY, GEORGE ROBERT (1848-1881), Anglo-Indian
writer, son of a Bengal chaplain, was born on the 25th
of July 1848, and was educated at Magdalen College School
and Cambridge University. Entering the Indian education
department in 1870, he became professor of English literature
in Delhi College in 1873, tutor to the raja of Rutlam
1876, and principal of the Rajkumar College at Indore in
1877. He is best known for his book Twenty-one Days in India
(1878--1879), a satire upon Anglo-Indian society and modes of
thought. This book gave promise of a successful literary
Career, but the author died at the age of thirty-three.
ABERNETHY, JOHN (1680-1740), Irish Presbyterian divine,
was born at Coleraine, county Londonderry, where his father
was Nonconformist minister, on the 19th of October 1680. In
his thirteenth year he entered the university of Glasgow, and
on concluding his course thore went on to Edinburgh, where
his intellectual and social attainments gained him a ready
entrance into the most cultured circles. Returning home he
received licence to preach from his Presbytery before he was
twenty-one. In 1701 he was urgently invited to accept charge
of an important congregation in Antrim; and after an interval
of two years, mostly spent in further study in Dublin, he
was ordained there on the 8th of August 1703. Here he did
notable work, both as a debater in the synods and assemblies
of his church and as an evangelist. In 1712 he lost his wife
(Susannah Jordan), and the loss desolated his life for many
years. In 1717 he was invited to the congregation of Usher's
Quay, Dublin, and contemporaneously to what was called the
Old Congregation of Belfast. The synod assigned him to
Dublin. After careful consideration he declined to accede,
and remained at Antrim. This refusal was regarded then as
ecclesisstical high-treason; and a controversy of the most
intense and disproportionate character followed, Abernethy
standing firm for religious freedom and repudiating the
sacerdotal assumptions of all ecclesiastical courts. The
controversy and quarrel bears the name of the two camps in the
conflict, the ``Subscribers'' and the ``Non-subscribers.''
Out-and-out evangelical as (John Abernethy was, there can
be no question that he and his associates sowed the seeds
of that after-struggle (1821--1840) in which, under the
leadership of Dr Henry Cooke, the Arian and Socinian elements
of the Irish Presbyterian Church were thrown out. Much of
what he contended for, and which the ``Subscribers'' opposed
bitterly, has been silently granted in the lapse of time.
In 1726 the ``Non-subscribers,'' spite of an almost wofully
pathetic pleading against separation by Abernethy, were cut
off, with due ban and solemnity, from the Irish Presbyterian
Church. In 1730, although a ``Non-subscriber,'' he was
invited to Wood Street, Dublin, whither he removed. In
1731 came on the greatest controversy in which Abernethy
engaged, viz. in relation to the Test Act nominally, but
practically on the entire question of tests and disabilities.
His stand was ``against all laws that, upon account of mere
differences of religious opinions and forms of worship,
excluded men of integrity and ability from serving their
country.'' He was nearly a century in advance of his age.
He had to reason with those who denied that a Roman Catholic
or Dissenter could be a ``man of integrity and ability.''
His Tracts---afterwards collected--did fresh service,
generations later, and his name is honoured by all who love
freedom of conscience and opinion. He died in December 1740.
See Dr Duchal's Life, prefixed to Sermons (1762): Diary in
MS., 6 vols. 4to; Reid's Presbyterian Church in Ireland, iii. 234.
ABERNETHY, JOHN (1764-1831), English surgeon, grandson of
John Abernethy (see above), was born in London on the 3rd of
April 1764. His father was a London merchant. Educated at
Wolverhampton grammar school, he was apprenticed in 1779 to
Sir Charles Blicke (1745-1815), surgeon to St Bartholomew's
Hospital, London. He attended the anatomical lectures of
Sir William Blizard (1743-1835) at the London Hospital,
and was early employed to assist as ``demonstrator'';
he also attended Percival Pott's surgical lectures at St
Bartholomew's Hospital, as well as the lectures of John
Hunter. On Pott's resignation of the office of surgeon of St
Bartholomew's, Sir Charles Blicke, who was assistant-surgeon,
succeeded him, and Abernethy was elected assistant-surgeon in
1787. In this capacity he began to give lectures at his
house in Bartholomew Close, which were so well attended
that the governors of the hospital built a regular theatre
(1790-1791), and Abernethy thus became the founder of the
distinguished school of St Bartholomew's. He held the office
of assistant-surgeon of the hospital for the long period of
twenty-eight years, till, in 1815, he was elected principal
surgeon. He had before that time been appointed lecturer in
anatomy to the Royal College of Surgeons (1814). Abernethy
was not a great operator, though his name is associated with
the treatment of aneurism by ligature of the external iliac
artery. His Surgical Observations on the Constitutional
Origin and Treatment of Local Diseases (1809)--known as ``My
Book,'' from the great frequency with which he referred his
patients to it, and to page 72 of it in particular, under that
name--was one of the earliest popular works on medical science,
He taught that local diseases were frequently the results
of disordered states of the digestive organs, and were to be
treated by purging and attention to diet. As a lecturer he was
exceedingly attractive, and his success in teaching was largely
attributable to the persuasiveness with which he enunciated his
views. It has been said, however, that the influence he exerted
on those who attended his lectures was not beneficial in this
respect, that his opinions were delivered so dogmatically,
and all who differed from him were disparaged and denounced
so contemptuously, as to repress instead of stimulating
inquiry. The celebrity he attained in his practice was due
not only to his great professional skill, but also in part
to the singularity of his manners. He used great plainness
of speech in his intercourse with his patients, treating them
often brusquely and sometimes even rudely. In the circle of
his family and friends he was courteous and affectionate; and
in all his dealings he was strictly just and honourable. He
resigned his position at St Bartholomew's Hospital in 1827,
and died at his residence at Enfield on the 20th of April 1831.
A collected edition of his works was published in 1830. A biography,
Memoirs of John Abernethy, by George Macilwain, appeared in 1853.
ABERRATION (Lat. ab, from or away, errare, to wander),
a deviation or wandering, especially used in the figurative
sense: as in ethics, a deviation from the truth; in pathology,
a mental derangement; in zoology and botany, abnormal
development or structure. In optics, the word has two special
applications: (1) Aberration of Light, and (2) Aberration
in Optical Systems. These subjects receive treatment below.
I. ABERIIATION OF LIGHT This astronomical phenomenon may
be defined as an apparent motion of the heavenly bodies; the
stars describing annually orbits more or less elliptical,
according to the latitude of the star; consequently at
any moment the star appears to be displaced from its true
position. This apparent motion is due to the finite velocity
of light, and the progressive motion of the observer with the
earth, as it performs its yearly course about the sun. It
may be familiarized by the following illustrations. Alexis
Claude Clairaut gave this figure: Imagine rain to be falling
vertically, and a person carrying a thin perpendicular tube
to be standing on the ground. If the bearer be stationary,
rain-drops will traverse the tube without touching its sides;
if, however, the person be walking, the tube must be inchued
at an angle varying as his velocity in order that the rain
may traverse the tube centrally. (J. J. L. de Lalande gave
the illustration of a roofed carriage with an open front: if
the carriage be stationary, no rain enters; if, however, it be
moying, rain enters at the front. The ``umbrella', analogy
is possibly the best known figure. When stationary, the most
efficient position in which to hold an umbrella is obviously
vertical; when walking, the umbrella must be held more and
more inclined from the vertical as the walker quickens his
pace. Another familiar figure, pointed Out by P. L. M. de
Maupertuis, is that a sportsman, when aiming at a bird on the
wing, sights his gun some distance ahead of the bird, the
distance being proportional to the velocity of the bird.
The mechanical idea, named the parallelogram of velocities,
permits a ready and easy graphical representation of these
facts. Reverting to the analogy of Clairaut, let AB (fig.
1) represent the velocity of the rain, and AC the relative
velocity of the person bearing the tube. The diagonal AD
of the parallelogram, of which AB and AC are adjacent sides,
will represent, both in direction and magnitude, the motion
of the rain as apparent to the observer. Hence for the
rain to centrally traverse the tube, this must be inclined
at an angle BAD to the vertical; this angle is conveniently
termed the aberration: due to these two motions. The
umbrella analogy is similarly explained; the most efficient
position heing when the stick points along the resultant AD.
The discovery of the aberration of light in 1725, due to James
Bradley, is one of the most important in the whole domain of
astronomy. That it wus unexpected there can be no doubt;
and it was only by extraordinary perseverance and perspicuity
that Bradley was able to explain it in 1727. Its origin is
seated in attempts made to free from doubt the prevailing
discordances as to whether the stars possessed appreciable
parallaxes. The Copernican theory of the solar system--that
the earth revolved annually about the sun--had received
confirmation by the observations of Galileo and Tycho
Brahe, and the mathematical investigations of Kepler and
Newton. As early as 1573, Thomas Digges had suggested that
this theory should necessitate a parallactic shifting of
the stars, and, consequently, if such stellar parallaxes
existed, then the Copernican theory would receive additional
confirmation. Many observers claimed to have determined such
parallaxes, but Tycho Brahe and G. B. Riccioll concluded
that they existed only in the minds of the observers, and
