See also:

• ABERRATION (Lat. ab, from or away, errare,, to wander)

ABERRATION (See also:

• LAT

Lat. ab, from or away, errare,, to wander)  , a deviation or wandering, especially used in the figurative sense: as in See also:

• ETHICS
• ETHICS, SHAFTESBURY, HOBBES

ethics, a deviation from the truth; in See also:

• PATHOLOGY (from Gr. raBos, suffering)

pathology, a See also:

• MENTAL

mental derangement; in See also:

• ZOOLOGY (from Gr. Nov, a living thing, and ?byos, theory)

zoology and See also:

• BOTANY (from Gr. l3or6v17, plant; ,66vicety, to graze)

botany, abnormal development or structure . In See also:

• OPTICS

optics, the word has two See also:

• SPECIAL

special applications: (I) See also:

• ABERRATION (Lat. ab, from or away, errare,, to wander)

Aberration of See also:

• LIGHT

Light, and (2) Aberration in See also:

• OPTICAL

Optical Systems . These subjects receive treatment below . I . ABERRATION OF LIGHT This astronomical phenomenon may be defined as an apparent See also:

• MOTION (Lat. motio, from movere, to move)
• MOTION, LAWS OF

motion of the heavenly bodies; the stars describing annually orbits more or less elliptical, according to the See also:

• LATITUDE (Lat. latitudo, latus, broad)

latitude of the See also:

• STAR

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 See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth, as it performs its yearly course about the See also:

• SUN
• SUN (0. Eng. sonne, Ger. sonne. Fr. soleil, Lat. sol, Gr. ijXior, from which comes helio- in various English compounds)

sun . It may be familiarized by the following illustrations . See also:

• ALEXIS
• ALEXIS, WILLIBALD

Alexis See also:

• CLAUDE, JEAN (1619-1687)

Claude Clairaut gave this figure: Imagine See also:

• RAIN (O.E. regn; the word is common to Teutonic languages, cf. Ger. Regen, Swed. and Dan. regn; it has been connected with Lat. rigare, to wet, Gr. 13pixeav)

rain to be falling vertically, and a See also:

• PERSON, OFFENCES AGAINST THE

person carrying a thin perpendicular See also:

• TUBE (Lat. tuba)

tube to be See also:

• STANDING

standing on the ground . If the See also:

• BEARER

bearer be stationary, rain-drops will See also:

• TRAVERSE

traverse the tube without touching its sides; if, however, the person be walking, the tube must be inclined at an See also:

• ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

angle varying as his velocity in See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order that the rain may traverse the tube centrally . J . J . L. de See also:

• LALANDE, JOSEPH JEROME LEFRANCAIS DE (1732-1807)

Lalande gave the See also:

• ILLUSTRATION

illustration of a'roofed See also:

• CARRIAGE

carriage with an open front: if the carriage be stationary, no rain enters; if, however, it be moving, rain enters at the front .

The " See also:

• UMBRELLA

umbrella " See also:

• ANALOGY (Gr. avaXo-yLa, proportion)

analogy is possibly the best known figure . When stationary, the most efficient position in which to hold an umbrella is obviously See also:

• VERTICAL (from Lat. vertex, highest point)

vertical; when walking, the umbrella must be held more and more inclined from the vertical as the See also:

• WALKER, FRANCIS AMASA (1840-1897)
• WALKER, FREDERICK (184o--1875)
• WALKER, GEORGE (c. 1618-169o)
• WALKER, HENRY OLIVER (1843— )
• WALKER, HORATIO (1858– )
• WALKER, JOHN (1732—1807)
• WALKER, OBADIAH (1616-1699)
• WALKER, ROBERT (d. c. 1658)
• WALKER, ROBERT JAMES (1801-1869)
• WALKER, SEARS COOK (1805—1853)
• WALKER, THOMAS (1784—1836)
• WALKER, WILLIAM (1824-1860)

walker quickens his See also:

• PACE (through O. Fr. pas, from Lat. passus, step, properly the stretch of the leg in walking, from pandere, to stretch)
• PACE, RICHARD (c. 1482-1536)

pace . Another See also:

• FAMILIAR (through the Fr. familier, from Lat. familiaris, of or belonging to the familia, family)

familiar figure, pointed out by P . L . M. de See also:

• MAUPERTUIS, PIERRE LOUIS MOREAU DE (1698–1759)

Maupertuis, is that a sportsman, when aiming at a See also:

• BIRD

bird on the wing, See also:

• SIGHTS

sights his See also:

• GUN

gun some distance ahead of the bird, the distance being proportional to the velocity of the bird . The See also:

• MECHANICAL

mechanical See also:

• IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

idea, named the parallelogram of velocities, permits a ready and easy graphical See also:

• REPRESENTATION

representation of these facts . Reverting to the analogy of Clairaut, let AB (fig . I) represent the velocity of the rain, and AC the relative velocity of the person bearing the tube . The See also:

• DIAGONAL (Gr. &a, through, ywvia, a corner)

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 See also:

• BAD, BCD

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 being when the stick points along the resultant AD . The See also:

• DISCOVERY

discovery of the aberration of light in 1725, due to See also:

• JAMES
• JAMES (Gr. 'IlrKw,l3or, the Heb. Ya`akob or Jacob)
• JAMES (JAMES FRANCIS EDWARD STUART) (1688-1766)
• JAMES, 2ND EARL OF DOUGLAS AND MAR(c. 1358–1388)
• JAMES, DAVID (1839-1893)
• JAMES, EPISTLE OF
• JAMES, GEORGE PAYNE RAINSFOP
• JAMES, HENRY (1843— )
• JAMES, JOHN ANGELL (1785-1859)
• JAMES, THOMAS (c. 1573–1629)
• JAMES, WILLIAM (1842–1910)
• JAMES, WILLIAM (d. 1827)

James See also:

• BRADLEY, GEORGE GRANVILLE (1821–1903)
• BRADLEY, JAMES (1693–1762)

Bradley, is one of the most important in the whole domain ofastronomy .

That it was 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 shade to See also:

• FREE

free from doubt the prevailing discordances as to whether the stars possessed appreciable parallaxes . The Copernican theory of the See also:

• SOLAR, SOLLER (Lat. solarium, Fr.• galetas, Ital. solaio)

solar See also:

• SYSTEM

system—that the earth revolved annually about the sun—had received See also:

• CONFIRMATION (Lat. confirmatio, from confirmare, to establish, make firm)

confirmation by the observations of Galileo and Tycho See also:

• BRAHE, PER, COUNT (1602-1680)
• BRAHE, TYCHO (1546-1601)

Brahe, and the mathematical' investigations of See also:

• KEPLER, JOHANN (1571-1630)

Kepler and See also:

• NEWTON
• NEWTON, ALFRED (1829–1907)
• NEWTON, JOHN (1725-1807)
• NEWTON, JOHN (1823-1895)
• NEWTON, SIR CHARLES THOMAS (1816-1894)
• NEWTON, SIR ISAAC (1642-1727)

Newton . As See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

early as 1573, See also:

• THOMAS
• THOMAS (c. 1654-1720)
• THOMAS (d. 110o)
• THOMAS, ARTHUR GORING (1850-1892)
• THOMAS, CHARLES LOUIS AMBROISE (1811-1896)
• THOMAS, GEORGE (c. 1756-1802)
• THOMAS, GEORGE HENRY (1816-187o)
• THOMAS, ISAIAH (1749-1831)
• THOMAS, PIERRE (1634-1698)
• THOMAS, SIDNEY GILCHRIST (1850-1885)
• THOMAS, ST
• THOMAS, THEODORE (1835-1905)
• THOMAS, WILLIAM (d. 1554)

Thomas See also:

• DIGGES, WEST (172o-1786)

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 . Riccioli concluded that they existed only in the minds of the observers, and were due to instrumental and See also:

• PERSONAL

personal errors . In 168o See also:

• JEAN

Jean See also:

• PICARD, LOUIS JOSEPH ERNEST (1821-1877)

Picard, in his Voyage d' Uranibourg, stated, as a result of ten years' observations, that Polaris, or the See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

Pole Star, exhibited See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

variations in its position amounting to 40" annually; some astronomers endeavoured to explain this by See also:

• PARALLAX (Gr. aapa?X6, alternately)

parallax, but these attempts were futile, for the motion was at variance with that which parallax would occasion . J . See also:

• FLAMSTEED, JOHN (1646-1719)

Flamsteed, from measurements made in 1689 and succeeding years with his mural quad-rant, similarly concluded that the See also:

• DECLINATION (from Lat. declinare, to decline)

declination of the Pole Star was 40" less in See also:

• JULY

July than in See also:

• SEPTEMBER (Lat. septem, seven)

September . R . See also:

• HOOKE, ROBERT (1635–1703)

Hooke, in 1674, published his observations of y Draconis, a star of the second magnitude which passes practically overhead in the latitude of See also:

• LONDON

London, and whose observations are therefore singularly free from the complex corrections due to astronomical See also:

• REFRACTION
• REFRACTION (Lat. refringere, to break open or apart)

refraction, and concluded that this star was 23" more northerly in July than in See also:

• OCTOBER

October .

When James Bradley and See also:

• SAMUEL

Samuel See also:

• MOLYNEUX

Molyneux entered this See also:

• SPHERE (Gr. vclsa?pa, a ball or globe)

sphere of astronomical See also:

• RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

research in 1725, there consequently prevailed much uncertainty as to whether stellar parallaxes had been observed or not; and it was with the intention of definitely answering this question that these astronomers erected a large See also:

• TELESCOPE

telescope at the See also:

• HOUSE
• HOUSE (O. Eng. hiss, a word common to Teutonic languages, cf. Dut. huis, Ger. Haus; in Gothic it is only found in gudhiss, a temple; it may be ultimately connected with the root of " hide," conceal)

house of the latter at See also:

• KEW

Kew . They determined to reinvestigate the motion of y Draconis; the telescope, constructed by See also:

• GEORGE
• GEORGE, 8TH MARQUESS OF TWEEDDALE (1787-1876)
• GEORGE, HENRY (1839—1897)
• GEORGE, LAKE
• GEORGE, SAINT (d. 303)

George See also:

• GRAHAM, SIR GERALD (1831–1899)
• GRAHAM, SIR JAMES ROBERT GEORGE
• GRAHAM, SYLVESTER (1794-1851)
• GRAHAM, THOMAS (1805-1869)

Graham (1675-1751), a celebrated See also:

• INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument-maker, was affixed to a vertical See also:

• CHIMNEY (through the Fr. cheminee, from caminata, sc. camera, a Lat. derivative of caminus, an oven or furnace)

chimney stack, in such manner as to permit a small oscillation of the eyepiece, the amount of which, i.e. the deviation from the vertical, was regulated and measured by the introduction of a See also:

• SCREW (O.E. scrue, from O. Fr. escroue, mod. ecrou; ultimate origin uncertain; the word, or a similar one, appears in Teutonic languages, cf. Ger. Schraube, Dan. skrue, but Skeat, following Diaz, finds the origin in Lat. scrobs, a ditch, hole, particularl

screw and a plumb-See also:

• LINE

line . The instrument was set up in See also:

• NOVEMBER (Lat. novem, nine)

November 1725, and observations on y Draconis were made on the 3rd, 5th, 11th, and 12th of See also:

• DECEMBER (Lat. decent, ten)

December . There was apparently no shifting of the star, which was therefore thought to be at its most southerly point . On the 17th of December, however, Bradley observed that the star was moving southwards, a motion further shown by observations on the loth . These results were unexpected, and, in fact, inexplicable by existing theories; and an examination of the telescope showed that the observed anomalies were not due to instrumental errors . The observations were continued, and the star was seen to continue its southerly course until See also:

• MARCH
• MARCH (1) (from Fr. marcher, to walk; the earliest sense in French appears to be " to trample," and the origin has usually been found in the Lat. marcus, hammer; Low Lat. marcare, to hammer; hence to beat the road with the regular tread of a soldier: cf.
• MARCH, AUZIAS (c. "1395-1458)
• MARCH, EARLS OF
• MARCH, FRANCIS ANDREW (1825– )

March, when it took up a position some co" more southerly than its December position . After March it began to pass See also:

• NORTH
• NORTH, BARONS
• NORTH, MARIANNE (1830—1890)
• NORTH, ROGER (1653-1734)
• NORTH, SIR THOMAS (1535?-16o1?)

north-wards, a motion quite apparent by the See also:

• MIDDLE

middle of See also:

• APRIL

April; in See also:

• JUNE

June it passed at the same distance from the See also:

• ZENITH (from the Arabic)

zenith as it did in December; and in September it passed through its most northerly position, the extreme range from north to See also:

• SOUTH
• SOUTH, ROBERT (1634–1716)

south, i.e. the angle between the March and September positions, being 40" . This motion is evidently not due to parallax, for, in this See also:

• CASE
• CASE, JOHN (d. 1600)

case, the maximum range should be between the June and December positions; neither was it due to observational errors . Bradley and Molyneux discussed several hypotheses in the See also:

• HOPE, ANTHONY
• HOPE, THOMAS (c. 1770-1831)

hope of fixing the See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution . One See also:

• HYPOTHESIS (from Gr. inrorcOivat, to put under; cf. Lat. suppositio, from sub-ponere)

hypothesis was: while y Draconis was stationary, the plumb-line, from which the angular measurements were made, varied; this would follow if the See also:

• AXIS (Lat. for " axle ")

axis of the earth varied . The oscillation of the earth's axis may arise in two distinct ways; distinguished as " See also:

• NUTATION (from Lat. nutare, to nod)

nutation of the axis " and " variation of latitude .

" Nutation, the only See also:

• FORM (Lat. forma)

form of oscillation imagined by Bradley, postulates that while' the earth's c A axis is fixed with respect to the earth, i.e. the north and south poles occupy permanent See also:

• GEOGRAPHICAL

geographical positions, yet the axis is not directed towards a fixed point in the heavens; variation of latitude, however, is associated with the shifting of the axis within the earth, i.e. the geographical position of the north pole varies . Nutation of the axis would determine a similar apparent motion for all stars: thus, all stars having the same polar distance as y Draconis should exhibit the same apparent motion after or before this star by a See also:

• CONSTANT, BENJAMIN (1845-1902)

constant See also:

• INTERVAL

interval . Many stars satisfy the See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition of equality of polar distance with that of y Draconis, but few were See also:

• BRIGHT, JOHN (1811-188g)
• BRIGHT, SIR CHARLES TILSTON

bright enough to be observed in Molyneux's telescope . One such star, however, with a right See also:

• ASCENSION
• ASCENSION, FEAST OF THE

ascension' nearly equal to that of y Draconis, but in the opposite sense, was selected and kept under observation . This star was seen to possess an apparent motion similar to that which would be a consequence of the nutation of the earth's axis; but since its declination varied only one See also:

• HALF

half as much as in the case of y Draconis, it was obvious that nutation did not See also:

• SUPPLY (through Fr. from Lat. supplere, to fill up)

supply the requisite solution . The question as to whether the motion was due to an irregular See also:

• DISTRIBUTION (Lat. distribuere, to deal out)

distribution of the earth's See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere, thus involving abnormal variations in the refractive See also:

• INDEX

index, was also investigated; here, again, negative results were obtained . Bradley had already perceived, in the case of the two stars previously scrutinized, that the apparent difference of declination from the ihaximum positions was nearly proportional to the sun's distance from the equinoctial points; and he realized the See also:

• NECESSITY (Lat. necessitas)

necessity for more observations before any generalization could be attempted . For this purpose he repaired to the Rectory, See also:

• WANSTEAD

Wanstead, then the See also:

• RESIDENCE (Latin residere, to remain behind, to dwell, reside)

residence of Mrs See also:

• POUND
• POUND (2)—(a)

Pound, the widow of his See also:

• UNCLE

uncle James Pound, with whom he had made many observations of the heavenly bodies . Here he had set up, on the rgth of See also:

• AUGUST (originally Sextilis)

August 1727, a more convenient telescope than that at Kew, its range extending over 6',-° on each See also:

• SIDE
• SIDE (mod. Eski Adalia)

side of the zenith, thus covering a far larger See also:

• AREA

area of the See also:

• SKY (M. Eng. skie, cloud; O. Eng. skua, shade; connected with an Indo-European root sku, cover, whence " scum," Lat. obscurus, dark, &c.)

sky . Two See also:

• HUNDRED

hundred stars in the See also:

• BRITISH

British See also:

• CATALOGUE (a Fr. adaptation of the Gr. KaraXoyos, a register, from Karalyety, to enrol or pick out)

Catalogue of Flamsteed traversed its See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field of view; and, of these, about fifty were kept under See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close observation . His conclusions may be thus summarized: (I) only stars near the solstitial See also:

• COLURE (from Gr. icoXos, shortened, and oupa, tail)

colure had their maximum north and south positions when the sun was near the equinoxes, (2) each star was'at its maximum positions when it passed the zenith at six o'See also:

• CLOCK

clock See also:

• MORNING

morning and evening (this he afterwards showed to be inaccurate, and found the greatest See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change in declination to be proportional to the latitude of the star), (3) the apparent motions of all stars at about the same See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time was in the same direction . A re-examination of his previously considered hypotheses as to the cause of these phenomena was fruitless; the true theory was ultimately discovered by a pure See also:

• ACCIDENT
• ACCIDENT (from Lat. accidere, to happen)

accident, comparable in simplicity and importance with the association of a falling See also:

• APPLE (a common Teut. word, A.S. aepl, aeppel, O.H.G. aphul, aphal, apfal, mod. Ger. Apfel)

apple with the discovery of the principle of universal See also:

• GRAVITATION (from Lat. gravis, heavy)

gravitation .

Sailing on the See also:

• RIVER

river See also:

• THAMES

Thames, Bradley repeatedly observed the shifting of a See also:

• VANE (formerly spelt " fane," i.e. pennon, flag; cf. Ger. Feline, Du. vaan, Fr. girouette, Ital. banderuola, Ger. Wellerfahne)
• VANE, SIR HENRY (1589-1654)
• VANE, SIR HENRY (1613-1662)

vane on the See also:

• MAST (2) (Anglo-Saxon maest, food, common to some Teutonic languages, and ultimately connected with " meat")
• MAST (I) (O. Eng. maest; a common Teutonic word, cognate with Lat. malus; from the medieval latinized form mast us comes Fr. malt)

mast as the See also:

• BOAT (0. Eng. bdt; the true etymological connexion with Dutch and Ger. boot, Fr. bateau, Ital. battello presents great difficulties; Celtic forms are from O. Eng.)

boat altered its course; and, having been assured that the motion of the vane meant that the boat, and not the See also:

• WIND
• WIND (a common Teut. word, cognate with Skt. vats, Lat. ventus, cf. " weather," to be of course distinguished from to " wind," to coil or twist, O.Eng. windan, cf. "wander," "wend," &c.)

wind, had altered its direction, he realized that the position taken up by the vane was determined by the motion of the boat and the direction of the wind . The application of this observation to the phenomenon which had so See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long perplexed him was not difficult, and, in 1727, he published his theory of the aberration of light—a corner-See also:

• STONE
• STONE (0. Eng. shin; the word is common to Teutonic languages, cf. Ger. Stein, Du. steen, Dan. and Swed. sten; the root is also seen in Gr. aria, pebble)
• STONE, CHARLES POMEROY (1824-1887)
• STONE, EDWARD JAMES (1831-1897)
• STONE, FRANK (1800-1859)
• STONE, GEORGE (1708—1764)
• STONE, LUCY [BLACKWELL] (1818-1893)
• STONE, MARCUS (184o— )
• STONE, NICHOLAS (1586-1647)

stone of the edifice of astronomical See also:

• SCIENCE (Lat. scientia, from scire; to learn, know)

science . Let S (fig . 2) be a star and the s observer be carried along the line AB; let SB be perpendicular to AB . If the observer be stationary at B, the star will appear in the direction BS; if, however, he traverses the distance BA in the same time as light passes from the star to his See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye, the star will appear in the direction AS . Since, however, the ob- server is not conscious of his own translatory motion a displacement which is at all times parallel to the motion of the observer . To generalize this, let S (fig .