[1] The invention of "aethers" is to be carried back, at least, to
the Greek philosophers, and with the growth of knowledge they were
empirically postulated to explain many diverse phenomena. Only one
"aether" has survived in modern science--that associated with light
and electricity, and of which Lord Salisbury, in his presidential
address to the British Association in 1894, said, "For more than two
generations the main, if not the only, function of the word 'aether'
has been to furnish a nominative case to the verb 'to undulate.'"
(See AETHER.)
[2] With the Greeks the word "Optics" or [Greek: Optika] (from
[Greek: optomai], the obsolete present of [Greek: orô], I see) was
restricted to questions concerning vision, &c., and the nature of
light.
[3] It seems probable that spectacles were in use towards the end of
the 13th century. The Italian dictionary of the _Accademici della
Crusca_ (1612) mentions a sermon of Jordan de Rivalto, published in
1305, which refers to the invention as "not twenty years since"; and
Muschenbroek states that the tomb of Salvinus Armatus, a Florentine
nobleman who died in 1317, bears an inscription assigning the
invention to him. (See the articles TELESCOPE and CAMERA OBSCURA for
the history of these instruments.)
[4] Newton's observation that a second refraction did not change the
colours had been anticipated in 1648 by Marci de Kronland
(1595-1667), professor of medicine at the university of Prague, in
his _Thaumantias_, who studied the spectrum under the name of _Iris
trigonia_. There is no evidence that Newton knew of this, although he
mentions de Dominic's experiment with the glass globe containing
water.
[5] The geometrical determination of the form of the surface which
will reflect, or of the surface dividing two media which will
refract, rays from one point to another, is very easily effected by
using the "characteristic function" of Hamilton, which for the
problems under consideration may be stated in the form that "the
optical paths of all rays must be the same." In the case of
reflection, if A and B be the diverging and converging points, and P
a point on the reflecting surface, then the locus of P is such that
AP + PB is constant. Therefore the surface is an ellipsoid of
revolution having A and B as foci. If the rays be parallel, i.e. if A
be at infinity, the surface is a paraboloid of revolution having B as
focus and the axis parallel to the direction of the rays. In
refraction if A be in the medium of index µ, and B in the medium of
index µ´, the characteristic function shows that µAP + µ´PB, where P
is a point on the surface, must be constant. Plane sections through A
and B of such surfaces were originally investigated by Descartes, and
are named Cartesian ovals. If the rays be parallel, i.e. A be at
infinity, the surface becomes an ellipsoid of revolution having B for
one focus, µ´/µ for eccentricity, and the axis parallel to the
direction of the rays.
[6] Young's views of the nature of light, which he formulated as
_Propositions_ and _Hypotheses_, are given _in extenso_ in the
article INTERFERENCE. See also his article "Chromatics" in the
supplementary volumes to the 3rd edition of the _Encyclopaedia
Britannica_.
[7] A crucial test of the emission and undulatory theories, which was
realized by Descartes, Newton, Fermat and others, consisted in
determining the velocity of light in two differently refracting
media. This experiment was conducted in 1850 by Foucault, who showed
that the velocity was less in water than in air, thereby confirming
the undulatory and invalidating the emission theory.
[8] Newton, _Opticks_ (London, 1704).
[9] _Trans. Irish Acad._ 15, p. 69 (1824); 16, part i. "Science," p.
4 (1830), part ii., _ibid._ p. 93 (1830); 17, part i., p. 1 (1832).
[10] This kind of type will always be used in this article to denote
vectors.
[11] _Phil. Trans._ (1802), part i. p. 12.
[12] _Oeuvres complètes de Fresnel_ (Paris, 1866). (The researches
were published between 1815 and 1827.)
[13] _Ann. Phys. Chem._ (1883), 18, p. 663.
[14] H. A. Lorentz, _Zittingsversl. Akad. v. Wet. Amsterdam, 4_
(1896), p. 176.
[15] H. A. Lorentz, _Abhandlungen über theoretische Physik_, 1
(1907), p. 415.
[16] Clerk Maxwell, _A Treatise on Electricity and Magnetism_
(Oxford, 1st ed., 1873).
[17] H. Abraham, _Rapports présentés au congrès de physique de 1900_
(Paris), 2, p. 247.
[18] Ibid., p. 225.
[19] _Phil. Trans._, 175 (1884), p. 343.
[20] _Ann. d. Phys. u. Chem._ 155 (1875), p. 403.
[21] Ibid. 153 (1874), p. 525.
[22] _Ann. d. Phys_. 11 (1903), p. 873.
[23] _Phys. Review_, 13 (1901), p. 293.
[24] _Hertz, Untersuchungen über die Ausbreitung der elektrischen
Kraft_ (Leipzig, 1892).
[25] A. Righi, _L'Ottica delle oscillazioni elettriche_ (Bologna,
1897); P. Lebedew, _Ann. d. Phys. u. Chem._, 56 (1895), p. 1.
[26] "Reflection and Refraction," _Trans. Cambr. Phil. Soc._ 7, p. 1
(1837); "Double Refraction," ibid. p. 121 (1839).
[27] "Double Refraction," _Ann. d. Phys. u. Chem._ 25 (1832), p. 418;
"Crystalline Reflection," _Abhandl. Akad. Berlin_ (1835), p. 1.
[28] _Trans. Irish Acad._ 21, "Science," p. 17 (1839).
[29] _Math. and Phys. Papers_ (London, 1890), 3, p. 466.
[30] Helmholtz, _Ann. d. Phys. u. Chem._, 154 (1875), p. 582.
[31] H. A. Lorentz, _Versuch einer Theorie der elektrischen u.
optischen Erscheinungen in bewegten Körpern_ (1895) (Leipzig, 1906);
J. Larmor, _Aether and Matter_ (Cambridge, 1900).
LIGHTFOOT, JOHN (1602-1675), English divine and rabbinical scholar, was
the son of Thomas Lightfoot, vicar of Uttoxeter, Staffordshire, and was
born at Stoke-upon-Trent on the 29th of March 1602. His education was
received at Morton Green near Congleton, Cheshire, and at Christ's
College, Cambridge, where he was reckoned the best orator among the
undergraduates. After taking his degree he became assistant master at
Repton in Derbyshire; after taking orders he was appointed curate of
Norton-under-Hales in Shropshire. There he attracted the notice of Sir
Rowland Cotton, an amateur Hebraist of some distinction, who made him
his domestic chaplain at Bellaport. Shortly after the removal of Sir
Rowland to London, Lightfoot, abandoning an intention to go abroad,
accepted a charge at Stone in Staffordshire, where he continued for
about two years. From Stone he removed to Hornsey, near London, for the
sake of reading in the library of Sion College. His first published
work, entitled _Erubhin, or Miscellanies, Christian and Judaical, penned
for recreation at vacant hours_, and dedicated to Sir R. Cotton,
appeared at London in 1629. In September 1630 he was presented by Sir R.
Cotton to the rectory of Ashley in Staffordshire, where he remained
until June, 1642, when he went to London, probably to superintend the
publication of his next work, _A Few and New Observations upon the Book
of Genesis: the most of them certain; the rest, probable; all, harmless,
strange and rarely heard of before_, which appeared at London in that
year. Soon after his arrival in London he became minister of St
Bartholomew's church, near the Exchange; and in 1643 he was appointed to
preach the sermon before the House of Commons on occasion of the public
fast of the 29th of March. It was published under the title of _Elias
Redivivus_, the text being Luke i. 17; in it a parallel is drawn between
the Baptist's ministry and the work of reformation which in the
preacher's judgment was incumbent on the parliament of his own day.
Lightfoot was also one of the original members of the Westminster
Assembly; his "Journal of the Proceedings of the Assembly of Divines
from January 1, 1643 to December 31, 1644," now printed in the
thirteenth volume of the 8vo edition of his _Works_, is a valuable
historical source for the brief period to which it relates. He was
assiduous in his attendance, and, though frequently standing almost or
quite alone, especially in the Erastian controversy, he exercised a
material influence on the result of the discussions of the Assembly. In
1643 Lightfoot published _A Handful of Gleanings out of the Book of
Exodus_, and in the same year he was made master of Catharine Hall by
the parliamentary visitors of Cambridge, and also, on the recommendation
of the Assembly, was promoted to the rectory of Much Munden in
Hertfordshire; both appointments he retained until his death. In 1644
was published in London the first instalment of the laborious but never
completed work of which the full title runs _The Harmony of the Four
Evangelists among themselves, and with the Old Testament, with an
explanation of the chiefest difficulties both in Language and Sense:
Part I. From the beginning of the Gospels to the Baptism of our
Saviour._ The second part _From the Baptism of our Saviour to the first
Passover after_ followed in 1647, and the third _From the first Passover
after our Saviour's Baptism to the second_ in 1650. On the 26th of
August 1645 he again preached before the House of Commons on the day of
their monthly fast. His text was Rev. xx. 1, 2. After controverting the
doctrine of the Millenaries, he urged various practical suggestions for
the repression with a strong hand of current blasphemies, for a thorough
revision of the authorized version of the Scriptures, for the
encouragement of a learned ministry, and for a speedy settlement of the
church. In the same year appeared _A Commentary upon the Acts of the
Apostles, chronical and critical; the Difficulties of the text
explained, and the times of the Story cast into annals. From the
beginning of the Book to the end of the Twelfth Chapter. With a brief
survey of the contemporary Story of the Jews and Romans_ (down to the
third year of Claudius). In 1647 he published _The Harmony, Chronicle,
and Order of the Old Testament_, which was followed in 1655 by _The
Harmony, Chronicle, and Order of the New Testament_, inscribed to
Cromwell. In 1654 Lightfoot had been chosen vice-chancellor of the
university of Cambridge, but continued to reside by preference at
Munden, in the rectory of which, as well as in the mastership of
Catharine Hall, he was confirmed at the Restoration. The remainder of
his life was devoted to helping Brian Walton with the Polyglot Bible
(1657) and to his own best-known work, the _Horae Hebraicae et
Talmudicae_, in which the volume relating to Matthew appeared in 1658,
that relating to Mark in 1663, and those relating to 1 Corinthians, John
and Luke, in 1664, 1671 and 1674 respectively. While travelling from
Cambridge to Ely (where he had been collated in 1668 by Sir Orlando
Bridgman to a prebendal stall), he caught a severe cold, and died at Ely
on the 6th of December 1675. The _Horae Hebraicae et Talmudicae impensae
in Acta Apostolorum et in Ep. S. Pauli ad Romanos_ were published
posthumously.
The _Works_ of Lightfoot were first edited, in 2 vols. fol., by G.
Bright and Strype in 1684; the _Opera Omnia, cura Joh. Texelii_,
appeared at Rotterdam in 1686 (2 vols. fol.), and again, edited by J.
Leusden, at Franeker in 1699 (3 vols. fol.). A volume of _Remains_ was
published at London in 1700. The _Hor. Hebr. et Talm_. were also
edited in Latin by Carpzov (Leipzig, 1675-1679), and again, in
English, by Gandell (Oxford, 1859). The most complete edition is that
of the _Whole Works_, in 13 vols. 8vo, edited, with a life, by R.
Pitman (London, 1822-1825). It includes, besides the works already
noticed, numerous sermons, letters and miscellaneous writings; and
also _The Temple, especially as it stood in the Days of our Saviour_
(London, 1650).
See D. M. Welton, _John Lightfoot, the Hebraist_ (Leipzig, 1878).