_Oxygen in the Sun._--In 1877 Professor Draper announced the discovery of oxygen lines in the spectrum of the sun. The discovery was doubted, and the methods used were criticised by Lockyer and others, but later and more delicate experiments substantiate Professor Draper's claim to the discovery. The elements known to exist in the sun are salt, iron, hydrogen, [Page 271] magnesium, barium, copper, zinc, cromium, and nickel. Some elements in the sun are scarcely, if at all, discoverable on the earth, and some on the earth not yet discernible in the sun.

_Substance of Stars._--Aldebaran (_Frontispiece_) shows salt, magnesium, hydrogen, calcium, iron, bis.m.u.th, tellurium, antimony, and mercury.

Some of the sun's metals do not appear. Stars differ in their very substance, and will, no doubt, introduce new elements to us unknown before.

The theory that all nebulae are very distant cl.u.s.ters of stars is utterly disproved by the clearest proof that some of them are only incandescent gases of one or two kinds.

_Discoveries of New Bodies._--Vulcan, the planet nearest the sun (page 138). The two satellites of Mars were discovered by Mr. Hall, U. S. Naval Observatory, August 11th, 1877 (page 161). "The outer one is called Diemas; the inner, Phobus.

Sir William Herschel thought he discovered six satellites of Ura.n.u.s.

The existence of four of them has been disproved by the researches of men with larger telescopes. Two new ones, however, were discovered by Mr. La.s.sell in 1846.

_Saturn's Rings_ are proved to be in a state of fluidity and contraction (page 171).

_Meteors and Comets._--The orbits of over one hundred swarms of meteoric bodies are fixed: their relation to, and in some cases indent.i.ty with, comets determined. Some comets are proved to be ma.s.ses of great weight and solidity (page 133).

_Aerolites._-Some have a texture like our lowest strata of rocks.

There is a geology of stars and meteors as well as of the earth. M.

Meunier has just received the Lalande Medal from the Paris Academy for his treatise showing that, so far as our present knowledge can determine, some of these meteors once belonged to a globe developed in true geological epochs, and which has been separated into fragments by agencies with which we are not acquainted.

[Ill.u.s.tration: Fig. 82.--Horizontal Pendulum.]

_The Horizontal Pendulum._--This delicate instrument is [Page 272]

represented in Fig. 82. It consists of an upright standard, strongly braced; a weight, _m_, suspended by the hair-spring of a watch, B D, and held in a horizontal position by another watch-spring, A C. The weight is deflected from side to side by the slightest influence.

The least change in the level of a base thirty-nine inches long that could be detected by a spirit-level is 0".1 of an arc--equal to raising one end 1/2068 of an inch. But the pendulum detects a raising of one end 1/36000000 of an inch. To observe the movements of the pendulum, it is kept in a dark room, and a ray of light is directed to the mirror, _m_, and thence reflected upon a screen.

Thus the least movement may be enormously magnified, and read and measured by the moving spot on the screen. It has been discovered that when the sun rises it has sufficient attraction to incline this instrument to the east; when it sets, to incline it to the west. The same is true of the moon. When either is exactly overhead or underfoot, of course there is no deflection. The mean deflection caused by the moon at rising or setting is 0".0174; by the sun, 0".008. Great results are expected from this instrument hardly known as yet: among others, whether gravitation acts instantly or consumes time in coming from the sun. This will be shown by the time of the change of the pendulum from east to west when the sun reaches the zenith, and _vice versa_ when it crosses the nadir. The sun will be best studied without light, in the quiet and darkness of some deep mine.

[Page 273]

_Light of Unseen Stars._--From careful examination, it appears that three-fourths of the light on a fine starlight night comes from stars that cannot be discerned by the naked eye. The whole amount of star light is about one-eightieth of that of the full moon.

_Lateral Movements of Stars_, page 226-28.

_Future Discoveries_--_A Trans-Neptunian Planet._--Professor Asaph Hall says: "It is known to me that at least two American astronomers, armed with powerful telescopes, have been searching quite recently for a trans-Neptunian planet. These searches have been caused by the fact that Professor Newcomb's tables of Ura.n.u.s and Neptune already begin to differ from observation. But are we to infer from these errors of the planetary tables the existence of a trans-Neptunian planet? It is possible that such a planet may exist, but the probability is, I think, that the differences are caused by errors in the theories of these planets. * * * A few years ago the remark was frequently made that the labors of astronomers on the solar system were finished, and that henceforth they could turn their whole attention to sidereal astronomy. But to-day we have the lunar theory in a very discouraging condition, and the theories of Mercury, Jupiter, Saturn, Ura.n.u.s, and Neptune all in need of revision; unless, indeed, Leverrier's theories of the last two planets shall stand the test of observation.

But, after all, such a condition of things is only the natural result of long and accurate series of observations, which make evident the small inequalities in the motions, and bring to light the errors of theory."

Future discoveries will mostly reveal the laws and conditions of the higher and finer forces. Already Professor Loomis telegraphs twenty miles without wire, by the electric currents between mountains.

We begin to use electricity for light, and feel after it for a motor. Comets and Auroras show its presence between worlds, and in the interstellar s.p.a.ces. Let another Newton arise.

[Page 274]

SOME ELEMENTS OF THE SOLAR SYSTEM ------------------------------------------------------------------------

Mean Dist.

from Sun.

-------------------

Mean

Density.

Earth's

Diameter

[Earth]

Name.

Sign.

Ma.s.ses.

Dist.

Millions

in Miles.

= 1.

as 1.

of Miles.

-----------

--------

------------

--------

----------

---------

--------

Sun

[Symbol]

Unity

860,000

0.255

Mercury

[Symbol]

1/5000000(?)

0.387

35-3/4

2,992

1.21

Venus

[Symbol]

1/425000

0.723

66-3/4

7,660

0.85

Earth

[Symbol]

1/326800

1.

92-1/3

7,918

1.

Mars

[Symbol]

1/2950000

1.523

141

4,211

0.737

Asteroids

(No.)

Jupiter

[Symbol]

1/1047

5.203

480

86,000

0.243

Saturn

[Symbol]

1/3501

9.538

881

70,500

0.133

Ura.n.u.s

[Symbol]

1/22600

19.183

1771

31,700

0.226

Neptune

[Symbol]

1/19380

30.054

2775

34,500

0.204

------------------------------------------------------------------------

-------------------------------------------------------------

Gravity

Axial

at

Orbital

Revolu-

Surface.

Periodic

Velocity

Name.

tion

[Earth]

Time.

in Miles

= 1

per sec.

-----------

---------------

----------

-----------

----------

Sun

25 to 26d

27.71

Mercury

24h 5m(?)

0.46

87.97d

29.55

Venus

23h 21m(?)

0.82

224.70d

21.61

Earth

23h 56m 4s

1.

365.26d

18.38

Mars

24h 37m 22.7s

0.39

686.98d

14.99

Asteroids

Jupiter

9h 55m 20s

2.64

11.86yrs

8.06

Saturn

10h 14m

1.18

29.46yrs

5.95

Ura.n.u.s

Unknown.

0.90

84.02yrs

4.20

Neptune

Unknown.

0.89

164.78yrs

3.36

-------------------------------------------------------------

[Page 275]

EXPLANATION OF ASTRONOMICAL SYMBOLS.

SIGNS OF THE ZODIAC

0. [Symbol] Aries 0

VI. [Symbol] Libra 180 I. [Symbol] Taurus 30

VII. [Symbol] Scorpio 210 II. [Symbol] Gemini 60

VIII. [Symbol] Sagittarius 240 III. [Symbol] Cancer 90

IX. [Symbol] Capricornus 270 IV. [Symbol] Leo 120

X. [Symbol] Aquarius 300 V. [Symbol] Virgo 150

XI. [Symbol] Pisces 330

[Symbol] Conjunction.

S. Seconds of Time.

[Symbol] Quadrature.

Degrees.

[Symbol] Opposition.

' Minutes of Arc.

[Symbol] Ascending Node.

" Seconds of Arc.

[Symbol] Descending Node.

R. A. Right Ascension.

H. Hours.

Decl. or D. Declination.

M. Minutes of Time.

N. P. D. Dist. From North Pole.

OTHER ABBREVIATIONS USED IN THE ALMANAC.

S., South, _i.e._, crosses the meridian; M., morning; A, Afternoon; Gr. H. L. N., greatest heliocentric lat.i.tude north, _i.e._, greatest distance north of the ecliptic, as seen from the sun. [Symbols]

Inf., inferior conjunction; Sup., superior conjunction.

GREEK ALPHABET USED INDICATING THE STARS.

a, alpha.

ae, eta.

n, nu.

t, tau.

b, beta.

th, theta.

x, xi.

u, upsilon.

g, gamma.

i, iota.

o, omicron.

ph, phi.

d, delta.

k, kappa.

p, pi.

ch, chi.

e, epsilon.

l, lambda.

r, rho.

ps, psi.

z, zeta.

m, mu.

s, sigma.

o, omega.

[Page 276]

CHAUTAUQUA OUTLINE FOR STUDENTS.

As an aid to comprehension, every student should draw ill.u.s.trative figures of the various circles, planes, and situations described.

(For example, see Fig. 45, page 112.) As an aid to memory, the portion of this outline referring to each chapter should be examined at the close of the reading, and this mere sketch filled up to a perfect picture from recollection.

I. _Creative Processes._--The dial-plate of the sky. Cause or different weights--on sun, moon. Two laws of gravity. Inertia. Fall of earth to sun per second. Forward motion. Elastic attraction. Perturbation of moon; of Jupiter and Saturn. Oscillations of planets.

II. _Light._--From condensation. Number of vibrations of red; violet.

Thermometer against air. Aerolite against earth. Two bolides against the sun. Large eye. Velocity of light. Prism. Color means different vibrations. Music of light. Light reports substance of stars. Force of; bridge, rain, dispersion, intensities, reflection, refraction, decomposition.

III. _Astronomical Instruments._--Refracting telescope. Reflecting; largest. Spectroscope. Spectra of sun, hydrogen, sodium, etc. E made G by approach; C by departure. Stars approach and recede.

IV. _Celestial Measurements._-Place and time by stars. Degrees, minutes, seconds. Mapping stars. Mural circle. Slow watch. Hoosac Tunnel. Fine measurements. Sidereal time. Spider-lines. Personal equation. Measure distance--height. Ten-inch base line. Parallax of sun, stars. Longitude at sea. Distance of Polaris, a Centauri, 61 Cygni. Orbits of asteroids.

V. _The Sun._--World on fire. Apparent size from planets. Zodiacal light. Corona. Hydrogen--how high? Size. How many earths? Spots: 1. Motion; 2. Edges; 3. Variable; 4. Periodic; 5. Cyclonic; 6.

Size; 7. Velocities. What the sun does. Experiments.

VI. _The Planets from s.p.a.ce._--North Pole. Speed. Sizes. Axial revolution. Man's weight on. Seasons. Parallelism of axis. Earth near [Page 277] sun in winter. Plane of ecliptic. Orbits inclined to. Earth rotates. Proof. Sun's path among stars. Position of planets. Motion--direct, retrograde. Experiments.

VII. _Meteors._--Size; number; cause of; above earth; velocity; colors; number in s.p.a.ce; telescopic view of. Aerolites: Systems of; how many known. Comets: Orbits; number of comets; Halley's; Biela's lost; Encke's. Resisting medium. Whence come comets? Composed of what? Amount of matter in. [Symbol].

VIII. _The Planets._--How many? Ura.n.u.s discovered? Neptune? Asteroids?