See also:

• EQUATORIAL

In astronomical practice is introduced a day, termed " sidereal,” determined, not by the diurnal revolution of the sun, but of the stars. The See also:

• YEAR

While it is true that the one is concerned altogether with See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

A body can move See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

The conception of force is, so to speak, elimitlated from the conditions of the problem, which is reduced to one of pure See also:

• KINEMATICS (from Gr. rciVI La, a motion)

In the actual problems of celestial mechanics three co-ordinates necessarily enter, leading to three differential equations and six equations of See also:

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

They afford yet another See also:

• GREAT

(3) See also:

• WHEWELL, WILLIAM (1794-1866)

The rigorous relation is expressed by a slight modification of the law. Putting M and m for the respective masses of the sun and planet, a for the semi-major axis of the orbit, and n for the mean angular motion in unit of time, the relation then is a3n2 M+m. What is noteworthy in this theorem is that this relation depends only on the sum of the masses. It follows, therefore, that were any portion of the mass of the sun taken from it, and added to the planet, the relation would be unchanged. Kepler's third law therefore expresses the fact that the mass of the sun is the same for all the planets, and deviates from the truth only to the extent that the masses of the latter differ from each other by quantities which are only a small fraction of the mass of the sun. Problem of Three Bodies.—As soon as the general law of gravitation was fully apprehended, it became evident that, owing to the attraction of each planet upon all the others, the actual motion of the planets must deviate from their motion in an ellipse according to Kepler's laws. In the Principia Newton made several investigations to determine the effects of these actions; but the geometrical method which he employed could See also:

• LEAD
• LEAD (pronounced iced)

Secondly, the law of conservation of areas. This is an See also:

• EXTENSION (Lat. ex, out ; tendere, to stretch)

The special conditions which obtain in the solar, system are such as to make the necessary approximation theoretically possible however complex the process may be. These conditions are: (i) The smallness of the masses of the planets in comparison with that of the sun, in consequence of which the orbit of each planet deviates but slightly from an ellipse during any one revolution; (2) the fact that the orbits of the planets are nearly circular, and the planes of their orbits but slightly inclined to each other. The result of these conditions is that all the quantities required admit of development in See also:

• SERIES (a Latin word from serere, to join)

, speed. It follows that the elements of the orbit admit of determination when the co-ordi- nates of the planet at an assigned moment Fie 2 and their derivatives as to time are given. Analytically the elements are determined from these data by solving the four equations just given, regarding a, b, c and d as unknown quantities, and x, y, x', y' and t as given quantities. The solution of these equations would lead to expressions of the form a=¢'(x,y,x',y',t) b = 02 (x,y,x',y',t) &c. &c. one for each of the elements. The general equations expressing the motion of a planet considered as a material particle round a centre of attraction lead to theorems the more interesting of which will now be enunciated. (i) The motion of such a planet may take place not only in an ellipse but in any curve of the second order; an ellipse, See also:

• HYPERBOLA

The simplest method of presenting it starts with the second view of the elliptic motion already set forth. We have shown that, when the position of a planet and the direction and speed of its motion at a certain instant are given, the elements of the orbit can be determined. We have supposed this to be done at a certain point P of the orbit, the direction and speed being expressed by the variables x, y, x' and y'. Now, consider the values of these same variables expressing the, position of the planet at a second point Q, and the speed with which it passes that point. With this position and speed the elements of the orbit can again be determined. Since the orbit is unchanged so See also:

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

If, with the changed velocity we again compute the elements they will be different from the former elements. But, if the impulse is not repeated, these new elements will again remain invariable. If repeated, the second impulse will again change the elements, and so on indefinitely. It follows that, if we go on computing the elements a, b, c, d from the actual values of x, y, x' and y', at each moment when the planet is subject to the attraction of another body, they will no longer be invariable, but will slowly vary from day to day and year to year. These ever varying elements represent an ever varying elliptic orbit,—not an orbit which the planet actually describes through its whole course, but an ideal one in which it is moving at each instant, and which continually adjusts itself to the actual motion of the planet at the instant. This is called the osculating orbit. The essential principle of Lagrange's elegant method consists in determining the See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

With these expressions we express their mutual action, or their pull upon each other at any and every moment. This pull determines the variations of the ideal elements. Knowing these variations it becomes ppossible to represent by integration the value of the elements as algebraic expressions containing the time, and the elements with which we started. But the variations thus determined will not be rigorously exact, because the pull from which they arise has been determined on the supposition that the planets are moving in unvarying orbits, whereas the actual pull depends on the actual position of the planets. Another approximation is, therefore, to be made, when necessary, by correcting the expression of the pull through taking account of the variations of the elements already determined, which will give a yet nearer approximation to the truth. In theory these successive approximations may be carried as far as we please, but in practice the labour of executing each approximation is so great that we are obliged to stop when the solution is so near the truth that the out-See also:

• STANDING

Of these modifications the most valuable is one conceived by P. A. See also:

• HANSEN, PETER ANDREAS (1795-1874)

Although this is true when there are any number of bodies moving in the same plane, the fact is that the planets move in slightly different planes. Hence the position of the plane of the orbit of each planet is continually changing in consequence of their mutual action. The problem of determining the changes is, however, simpler than others in perturbations. The method is again that of the variation of elements. The position and velocity being given in all three co-ordinates, a certain osculating plane is determined for each instant in which the planet is moving at that instant. This plane remains invariable so long as no third body acts ;' when it does act the position of the plane changes very slowly, continually rotating round the radius vector of the planet as an instantaneous axis of rotation. _ See also:

• SECULAR (Lat. saecularis, of or belonging to an age or generation, saeculum)

But, suppose the See also:

• TIDE (O. Eng. lid, cf. Ger. Zeit, time or season, connected with root of Sanskrit a-diti, endless)

We put Lo for its value at the moment from which the time is reckoned. The general expressipnfor the angle will then be L= nt +Lo..; Such an angle continually goes through the round of 36o in a definite period. For example, if the daily motion is 5°, and we take the day as the unit of time, the round will be completed in 72 days, and the angle will continually go through the value which it had 72 days before. Let us now consider an equation of the form U=a See also:

• SIN
• SIN (O. Eng. syn: a common Teutonic word, cf. Dutch zonde, Ger. Siinde)

The most interesting See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

These two motions, it will be seen, are in the proportion 5 : 2. The next conjunction will take place along CS', and the third after the initial one will again take place near the original position JQ, Jupiter having made five revolutions and Saturn two. The result of these repetitions is that, during a number of revolutions, the special mutual actions of the two planets at these three points of their orbits repeat themselves, while the actions corresponding to the three intermediate arcs are wanting. Thus it happens that if the mutual actions are balanced through a period of a few revolutions only there is a small residuum of forces corresponding to the three regions in question, which repeats itself in the same way, and which, if it continued indefinitely, would entirely change the forms of the two orbits. But the actual mean motions deviate slightly from the ratio 2 :'5, and we have next to show how this deviation results in an ultimate balancing of the forces. The annual mean motions, with the corresponding combinations, are as follows : Jupiter :—n =30°.349043 Saturn :—n' = 12 .221133 2n=6o .698o9 5n' = 61 .10567 5n'—2n= 0 •40758 If we make a more accurate computation of the conjunctions from these data, we shall find that, in the general mean, the consecutive conjunctions take place when each planet has moved through an entire number of revolutions+242.7°. It follows that the third conjunction instead of occurring exactly along the line CQ1 occurs along CQh, making an angle of nearly 8 with CQi. The successive conjunctions following will be along CRr, CS,, CQ3, &c., the law of progression being obvious. The balancing of the series of forces will not be complete until the respective triplets of conjunctions have filled up the entire space between them. This will occur when the angle whose annual motion is 5n'—2n has gone through 36o°. From the preceding value of5n'—2n we see that this will require a little more than 883 years. The result of the continued action of the two planets upon each other is that during half of this period the motion of one planet is constantly retarded and of the other constantly accelerated, while during the other half the effects are reversed.

There is thus in the case of each planet an oscillation of the mean longitude which increases it and then diminishes it to its original value at the end of the period of 884, years. he longitudes, latitudes and radii vectores of a planet, being algebraically expressed as the sum of an infinite periodic series of the kind we have been describing, it follows that the problem of finding their co-ordinates at any moment is solved by computing these expressions. This is facilitated by the construction of tables by means of which the co-ordinates can be computed at any time. Such tables are used in the offices of the See also:

• NATIONAL

Let the dotted lines show the direction of the distant attracting body. The point E, being more distant than C, will be attracted with less force, while Q will be attracted with a greater force than will the centre C. Were the force equal on every point of the earth it would have no influence on its rotation, but would simply draw FIG. 4. its whole mass toward the attracting body. It is therefore only the difference of the forces on different parts of the earth that affects the rotation. Let us, therefore, See also:

• DIVIDE

Here, however, the same action comes into play, which keeps a rotating See also:

• TOP (cf. Dan. top, Ger. Topf, also meaning pot)

The action of the sun upon the satellites of the several planets and the effects of this action are of the same general nature. For the same reason that the residual forces virtually act in opposite directions upon the nearer and more distant portions of a planet Fic. 3. they will virtually act in the case of a satellite. When the latter is between its See also:

• PRIMARY

The orbits of these bodies have a large inclination, nearly 27°, to the plane of the planet's orbit. The action of the sun alone would completely throw them out of these planes as each satellite orbit would rotate independently; but the effect of the mutual action is to keep all of the planes in See also:

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

Other works with the same general See also:

• OBJECT

At the base of every system of astronomical observation is the law that, in the voids of space, a See also:

• RAY (Lat. raia)
• RAY (or WRAY, as he wrote his name till 1670), JOHN (1628-1705)

It follows that if PO (fig. 5) is the direction of a ray, either from a heavenly body or from a terrestrial point, impinging at 0 upon the surface of quicksilver, and reflected in the direction OR, the vertical line is the bisector OZ, of the angle See also:

• POR

Let OF (fig. 7) be a section of the telescope, MN being its ------- ----- - - - -- - - FIG. 7. object See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

When the telescope is turned in this plane, the angular motion of the line of sight is equal to that through which the circle has turned. Stripped of all unnecessary adjuncts, and reduced to a geometric form, the ideal method by which the zenith distance of a heavenly body is determined by the combination which we have described is as follows:—Let OP (fig. 9) be the direction of a celestial body at which a telescope, supplied with a graduating circle, is pointed. Let OZ be an axis, as nearly vertical as it can easily be set, round which ASTRONOMY fs...F B A D FIG. 8. line of sight of the telescope pointing the entire See also:

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

When the basin of quicksilver is used, the telescope, either before or after being directed toward P, is pointed directly downwards, so that the observer mounting above it looks through it into the reflecting surface. He then adjusts the instrument so that the cross threads coincide with their images reflected from the surface of the quicksilver. The angular motion of the telescope in passing from this position to that when the celestial object is in the line of sight° is the distance (ND) of the body from the See also:

• NADIR (Arabic nadir, " opposite to," used elliptically for nadir-es-semt, "opposite to the zenith ")

By these two motions the instrument may be pointed first at one of the objects and then at the other. The motion of the graduated circle in passing from one pointing to the other is the measure of the difference between the longitudinal co-ordinates of the two objects. In the equatorial system this co-ordinate (the right ascension) is measured in a different way, by making the rotating earth perform the function of a graduated circle. The. unceasing diurnal motion of the image of any heavenly body relative to the cross threads of a telescope makes a direct accurate measure of any co-ordinate except the declination almost impossible. Before the position of a star can be noted, it has passed away from the cross threads. This trouble-some result is utilized and made a means of measurement. Right ascensions are now determined, not by measuring the angle between one star and another, but, by noting the time between the transits of successive stars over the meridian. The difference between these times, when reduced to an angle, is the difference of the right ascensions of the stars. The principle is the same as that by which the distance between two stations may be determined by the time required for a See also:

• TRAIN (M. Eng. trayn or trayne, derived through Fr. from Late Lat. trahinare, to drag, draw, Lat. trahere, cf. trail, trace, ultimately from the same source)

But this is not the true direction, because the ray of light from the object undergoes See also:

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

Next in extent of use are the transit instrument and the meridian circle, which are commonly See also:

• UNITED

(S. N.) History of Astronomy. A practical acquaintance with the elements of astronomy is indispensable to the conduct of human life. Hence it is most widely 'diffused among uncivilized ,peoples, whose existence depends upon immediate and unvarying vrioffhe tght submission to the dictates of See also:

• EXTERNAL

The Shu Chung further relates the tragic See also:

• FATE

Two instruments constructed at the time of Kublai See also:

• KHAN (from the Turki, hence Persian and Arabic Khan)

They took shape most likely, not through one stroke of invention, but incidentally, as legends developed and astrological persuasions became defined .° The zodiacal series in particular seem to have been reformed and reconstructed at wide intervals of time (see See also:

• ZODIAC (o i'w&arcds rvKcXor, from d,&ov, " a little animal ")

E. Dreyer, Proc. See also:

• ROY, WILLIAM (1726-1790)

4 Knowledge and Scientific See also:

• NEWS

F. X. Kugler T that the various periods underlying their lunar predictions were identical with those heretofore believed to have been independently arrived at by See also:

• HIPPARCHUS (fl. 146-126 B.c.)

es. while circulating round the earth, was the centre of revolution to Venus and Mercury.9 A genuine See also:

• HELIOCENTRIC

H. See also:

• COWELL, JOHN (1554—1611)

See also:

• EGYPTIAN

This fundamental advance rendered inevitable the detection of precessional effects. Aristarchus of Samos observed at Alexandria 280-264 B.C. His treatise on the magnitudes and distances of the sun and moon, edited by John See also:

• WALLIS, JOHN (1616-1703)

His loans from Chaldaean experts appear, indeed, to have been numerous; but were doubtless independently verified. His supreme merit, however, consisted in the See also:

• ESTABLISHMENT (0. Fr. establissement, Fr. etablissement, late Norm. Fr. establishement, from O. Fr. establir, Fr. etablir, Lat. stabilire, to make stable)

He further elaborated it by the introduction of " eccentrics," which accounted for the changes in orbital velocity of the sun and moon by a displacement of the earth, to a corresponding extent, from the centre of the circles they were assumed to describe. This gave the elliptic inequality known as the " equation of the centre," and no other was at that time obvious. He attempted no detailed discussion of planetary theory; but his catalogue of io8o stars, divided into six classes of brightness, or " magnitudes," is one of the finest monuments of antique astronomy. It is substantially embodied in Ptolemy's Almagest (see PTOLEMY). An interval of 250 years elapsed before the constructive labours of Hipparchus obtained completion at Alexandria. His observations were largely, and somewhat arbi- Ptolemy. trarily, employed by Ptolemy. Professor Newcomb, who has compiled an instructive table of the equinoxes severally observed by Hipparchus and Ptolemy, with their errors deduced from See also:

• LEVERRIER, URBAIN JEAN JOSEPH (1811—1877)

A.D. 400) and his daughter See also:

• HYPATIA ('Tiraria) (c. A.D. 370–415)

Ulugh Beg (1394-1449), a See also:

• GRANDSON (Ger. Grandsee)

Their See also:

• APPEARANCE (from Lat. apparere, to appear)

The See also:

• COLOSSAL

The Tabulae Prutenicae, calculated on Copernican principles by See also:

• ERASMUS, DESIDERIUS (1466–1536)

No more See also:

• CONGRUOUS (from Lat. congruere, to agree)

It states that the squares of the periods of circulation round the sun of the several planets are in the same ratio as the cubes of their mean distances. This numerical proportion, as being a necessary consequence of the law of gravitation, must prevail in every system under its sway. It does in fact prevail among the satellite-families of our acquaintance, and presumably in stellar combinations as well. Kepler's ineradicable belief in the existence of some such congruity was derived from the Pythagorean idea of an underlying See also:

• HARMONY (Gr. dpµovia, a concord of musical sounds, dpA'ew to join; &plan midi (sc. TeXvil)

Purbach. Observatory of Cassel. orbital relations of comets by his conviction of their perishable nature. He supposed their tails to result from the action of solar rays, which, in traversing their mass, bore off, with them some of their subtler particles to form trains directed away from the sun. And through the process of See also:

• WASTE (O. Fr. wast, guast, gast, gaste; Lat. vastus, vast, desolate)

The persistence of movement seemed to him to imply the persistence of a moving power. He did not recognize that motion and rest are equally natural, in the sense of requiring force for their alteration. Yet his rationale of the tides in De Motibus Stellae is not only memorable as an astonishing forecast of the principle of reciprocal attraction in the proportion of mass, but for its bold extension to the earth of the lunar sphere of influence. Galileo Galilei, Kepler's most eminent contemporary, took a foremost part in dissipating the obscurity that still hung over the very See also:

• FOUNDATIONS

Galileo's contributions to astronomy were of a different quality from Kepler's. They were easily intelligible to the general See also:

• CAMEO

And this was a Descartes. cul-de-See also:

• SAC

Gravitation was thus shown to be the See also:

• SOLE (Solea)

Euler devised in 1753 a new method, that of the " variation of parameters," for their investigation, and applied it to unravel some of the earth's irregularities in a memoir crowned, by the French See also:

• ACADEMY, GREEK
• ACADEMY, ROYAL

Johann Heinrich See also:

• LAMBERT [alias NICHOLSON], JOHN (d. 1538)
• LAMBERT, DANIEL (1770-1809)
• LAMBERT, FRANCIS (c 1486-153o)
• LAMBERT, JOHANN HEINRICH (1728–1777)
• LAMBERT, JOHN (1619-1694)

Researches into rotational movement were facilitated by S. D. See also:

• POISSON, SIMEON DENIS (1781-1840)

J. Leverrier, J. C. Adams, S. Newcomb, G. W. See also:

• HILL
• HILL (0. Eng. hyll; cf. Low Ger. hull, Mid. Dutch hul, allied to Lat. celsus, high, collis, hill, &c.)
• HILL, A
• HILL, AARON (1685-175o)
• HILL, AMBROSE POWELL
• HILL, DANIEL HARVEY (1821-1889)
• HILL, DAVID BENNETT (1843–1910)
• HILL, GEORGE BIRKBECK NORMAN (1835-1903)
• HILL, JAMES J
• HILL, JOHN (c. 1716-1775)
• HILL, MATTHEW DAVENPORT (1792-1872)
• HILL, OCTAVIA (1838– )
• HILL, ROWLAND (1744–1833)
• HILL, SIR ROWLAND (1795-1879)

Nor were these abstract investigations unaccompanied by See also:

• CONCRETE
• CONCRETE (Lat. concretes, participle of concrescere, to grow together)

The next was that of Venus on the 24th of November (O.S.) 1639, of which Jeremiah Horrocks and William Crabtree were the sole spectators. '00rro%s. The improvement of telescopes was prosecuted by Christiaan See also:

• HUYGENS, CHRISTIAAN (1629-1695)
• HUYGENS, SIR CONSTANTIJN (1596-1687)

No authoritative chief was assigned to it until 1771. G. D. See also:

• CASSINI

Cassini brought from Rome a 17-ft. telescope by G. Campani, with which he discovered in 1671 See also:

• IAPETUS

They have besides " proper motions," detected in 1718 by E. Halley in a few cases, and since found to prevail universally. Further, 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)

But his plan of attack was not happily chosen; he carried it out with deficient Haney. instrumental means; and his See also:

• ADMINISTRATION (Lat. administrare, to serve)

e. ne See also:

• DOLLOND, JOHN (1706—1761)

J. See also:

• DELAMBRE, JEAN BAPTISTE JOSEPH (1749-1822)

In See also:

• FRANCE
• FRANCE, ANATOLE (1844– )

Halley in 1716 ; they were later insisted upon by Lalande ; an See also:

• ENTHUSIASM

Again, since the constant of aberration defines the ratio between the velocity of light and the earth's orbital speed, the span of the terrestrial See also:

• CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

These were incidental trophies; See also:

• HERSCHEL, CAROLINE LUCRETIA (1750-1848)
• HERSCHEL, SIR F
• HERSCHEL, SIR FREDERICK WILLIAM (1738-1822)
• HERSCHEL, SIR JOHN FREDERICK WILLIAM, BART

A prolonged See also:

• SUCCESSION (Lat. successio, from succedere, to follow after)

With the Washington 26-in. refractor, See also:

• HALL
• HALL (generally known as SCHWABISCH-HALL, tc distinguish it from the small town of Hall in Tirol and Bad-Hall, a health resort in Upper Austria)
• HALL (O.E. heall, a common Teutonic word, cf. Ger. Halle)
• HALL, BASIL (1788-1844)
• HALL, CARL CHRISTIAN (1812–1888)
• HALL, CHARLES FRANCIS (1821-1871)
• HALL, CHRISTOPHER NEWMAN (1816—19oz)
• HALL, EDWARD (c. 1498-1547)
• HALL, FITZEDWARD (1825-1901)
• HALL, ISAAC HOLLISTER (1837-1896)
• HALL, JAMES (1793–1868)
• HALL, JAMES (1811–1898)
• HALL, JOSEPH (1574-1656)
• HALL, MARSHALL (1790-1857)
• HALL, ROBERT (1764-1831)
• HALL, SAMUEL CARTER (5800-5889)
• HALL, SIR JAMES (1761-1832)
• HALL, WILLIAM EDWARD (1835-1894)

The establishment of a class of " short-Comets period " comets by the computations of J. F. Encke in 1819, and of Wilhelm von Biela in. 1826; led to the theory of their " capture " by the great planets, for which a solid mathematical basis was provided by H. Newton, F. Tisse, See also:

• RAND

The See also:

• AFFINITY (Lat. affinitas, relationship by marriage, from offinis, bordering on, related to; finis, border, boundary)
• AFFINITY, CHEMICAL

J. Lalande, however, published in 18or, in his Histoire celeste, the approximate places of 47,390 from a reobservation of which the great Paris catalogue (1887-1892) has been compiled. A valuable catalogue of about 760o stars was issued by Giuseppe Piazzi in 1814; See also:

• STEPHEN
• STEPHEN (1097?-1154)
• STEPHEN (ISTVAN) BATHORY (1533-1586)
• STEPHEN, SIR JAMES (1789-1859)
• STEPHEN, SIR JAMES FITZJAMES, BART
• STEPHEN, SIR LESLIE (1832-1904)

Thome at See also:

• CORDOBA
• CORDOBA, GONZALO FERNANDEZ DE (1453–15.15)

form an indispensable part of stellar statistics; and metric their construction has been zealously prosecuted. "tat The Harvard See also:

• PHOTOMETRY (from Gr. (Pews, xarrbs, light, µerpov, a measure)

Kempf with a polarizing photometer; but by far the most comprehensive work of the kind is the Harvard Photometric Dwrehmusterung (1901-1903), embracing all stars to 7`5 magnitude, and extended to the southern pole by measurements executed' at Arequipa. The embarrassing subject of photo-graphic photometry has also been attacked by ProfessorPickering. The need is urgent of fixing a scale, and defining See also:

• STANDARDS

These' facilities were remarkably illustrated by Professor S. ,W. Burnham''s record of discovery, which roused fresh enthusiasm for this line of inquiry by compelling recognition of the extra-ordinary profusion throughout the heavens of See also:

• COMPOUND
• COMPOUND (from Lat. componere, to combine or put together)

And the data thus arrived at are reassuringly self-consistent. A wide photographic survey, by which parallaxes might be secured wholesale, has further been recommended by Kapteyn; but is unlikely to be undertaken Star catalogues. in the immediate future. The exhaustive ascertainment of stellar parallaxes, combined with the visible facts of stellar distribution, would enable us to build a perfect plan of the universe in three dimen- sions.. Its perfection would, nevertheless, be under- modoaathbper . mined by the mobility of all its constituent parts. Their configuration at a given instant supplies no information as to their configuration hereafter unless the mode and laws of their movements have been determined. Hence, one of the leading inducements to the construction of exact and comprehensive catalogues has been to elicit, by comparisons of those for widely separated epochs, the proper motions of the stars enumerated in them. Little was known on the subject at the beginning of the igth century. William Herschel founded his determination in 1783 of the sun's route in space upon the movements of thirteen stars; and he took into account those of only six in his second solution of the problem in 1805. But in 1837 Argelander employed 390 proper motions as materials for the treatment of the same subject; and L. Struve had at his disposal, in 1887, no less than 2800.

From the re-observation of Lalande's stars, after the See also:

• LAPSE (Lat. lapses, a slip or departure)

See also:

• CAMPBELL, ALEXANDER (1788–1866)
• CAMPBELL, BEATRICE STELLA (Mrs PATRICK CAMPBELL) (1865– )
• CAMPBELL, GEORGE (1719–1796)
• CAMPBELL, JOHN
• CAMPBELL, JOHN (1708-1775)
• CAMPBELL, JOHN CAMPBELL, BARON (1779-1861)
• CAMPBELL, JOHN FRANCIS
• CAMPBELL, LEWIS (1830-1908)
• CAMPBELL, REGINALD JOHN (1867— )
• CAMPBELL, THOMAS (1777—1844)

Partial anticipations abounded. The vital See also:

• HEART
• HEART, LUNG

Kirchhoff's principle, accordingly, not only afforded a simple explanation of the Fraunhofer lines, but availed to found a far-reaching science of celestial chemistry. Thousands of the dark lines in the solar spectrum agree absolutely in See also:

• WAVE

The See also:

• CORONA (Lat. for " crown ")

This was amply verified at subsequent eclipses. The photography of prominences was, after some preliminary trials by C. A. Young and others, fully realized. in i89r by Professor George E. See also:

• HALE, EDWARD EVERETT (1822-1909)
• HALE, HORATIO (1817–1896)
• HALE, JOHN PARKER (1806–1873)
• HALE, NATHAN (1756-1776)
• HALE, SIR MATTHEW (1609-1676)
• HALE, WILLIAM GARDNER (1849- )

See also:

• DONATI, GIOVANNI BATTISTA (1826-1873 )

A photograph of the spectrum of Tebbutt's comet, taken by him on the 24th of See also:

• JUNE

The progress of this survey was marked by a number of important discoveries of " new " and variable stars and of spectroscopic binaries, mainly through the acumen of Mrs Williamina See also:

• PATON, JOHN BROWN (1830- )
• PATON, SIR JOSEPH NOEL (1821-1901)

This subtle mode of research was made available by Sir William Huggins in 1868. He employed it, with an outcome of striking promise, to measure the radial speed of some of the brighter stars. In the following year, Sir Norman Lockyer was enabled to prove, by its means, the extraordinary vehemence of chromospheric disturbances, the bright prominence-rays in his spectroscope betraying, through their oppositeshiftings, movements and See also:

• COUNTER

Memoire sur 1'histoire des hypotheses astronomiques," Mimoires de 1'Institut, t. See also:

• XXX

Epping and J. N. Strassmeier, Astronomisches aus Babylon (1889); F. K. Ginzel, Die astronomischen Kenntnisse der Babylonier (1901) ; C. L.See also:

• IDELER, CHRISTIAN LUDWIG (1766–1846)

W. Hill, " Progress of Celestial Mechanics," The Observatory, vol. xix.(1896).