our sun is in motion. It is sweeping onward, win its retinue of worlds, 150,000,000 miles per year, toward a point in the constellation Hercules. The Pleiades has been thought to be the center around which this

great movement is taking place, but most astronomers consider the idea as a mere speculation.

The Number of the Fixed Stars.-When we look at the heavens on a clear night, the stars seem innumer

able. To count them, one would think almost as interminable a task as to number the leaves on the trees. It is, therefore, somewhat startling to learn that the entire number visible to the most piercing eyesight does not exceed 6,000, while few can discern more than 4,000.* The number, however, which may be seen with a telescope is marvellous. In Fig. 84, is shown a portion of the heavens where the naked eye sees but six stars. Could we examine the same region of the sky with more powerful instruments, new constellations would doubtless be descried in the infinite depths of space.

Scintillation.-The twinkling of the fixed stars is due to what is termed in Physics the "Interference of Light." The air, being unequally dense, warm, and moist in its various strata, transmits very irregularly the different colors of which white light is composed. Now one color prevails over the rest, and now another, so that the star appears to alter its hue incessantly. As the purity and density of the air vary, the twinkling of the stars also changes, and, therefore, it is always greatest near the horizon.†

Magnitude of the Stars.-As the telescope reveals no disk of even the nearest stars, we know nothing of their comparative size. The finest spider's thread, placed at the focus of the instrument, hides the star from the eye. When the moon passes in front of a

* This illusion may be easily explained, when we remember how the impression of a bright light remains upon the retina, as in the whirling of a firebrand.

+ Humboldt says that at Cumana, in South America, where the air is remarkably pure and uniform in density, the stars cease to twinkle after they have risen 15° above the horizon. This gives to the celestial vault a peculiarly calm and soft appearance.-It should be noticed that interference occurs only when the light emanates from a point. A body that subtends a visual angle, i. e., has a sensible disk, like a planet, cannot twinkle.

star, the occultation is instantaneous, and not gradual, as in the case of the planets. Classification depends, therefore, merely upon their relative brightness. The most conspicuous are termed stars of the first

magnitude; of these there are about twenty. The number of second-magnitude stars in the entire heavens is sixty-five; of the third, about 200; of the fifth, 1,100; of the sixth, 3,200; of the seventh, 13,000; of the eighth, 40,000; and of the ninth, 142,000. Few persons can see smaller stars than those of the fifth or sixth magnitude.

The Difference in the Brightness of the stars may result from a difference in their distance, size, or intrinsic brightness. Hence it follows that the faintest stars may not be the most distant from the earth.

Names of Stars.-Many of the brightest stars received proper names at an early date; as Sirius, Arcturus. The chief stars of each constellation are distinguished by the letters of the Greek alphabet ;*

the brightest one being usually called Alpha (a), the next Beta (8), etc.,-the name of the constellation, in the genitive case, being put after each. Ex., a Arietis, ẞ Lyræ.*

Star catalogues are issued, containing the stars arranged in the order of their Right Ascension, and numbered for convenience of reference. Argelander's Charts have 324,188 stars marked in the northern hemisphere.

The Constellations.-From the earliest ages, the stars have been arranged in constellations, for the purpose of more readily distinguishing them. Some of these groups were named from their supposed resemblance to certain figures, such as perching birds, pugnacious bulls, or contorted snakes, while others do honor to the memory of classic heroes.

"Thus monstrous forms, o'er heaven's nocturnal arch,
Seen by the sage, in pomp celestial march;
See Aries there his glittering bow unfold,
And raging Taurus toss his horns of gold;
With bended bow the sullen Archer lowers,
And there Aquarius comes with all his showers;
Lions and Centaurs, Gorgons, Hydras rise,
And gods and heroes blaze along the skies."

With a few exceptions, the likeness is purely fanciful. Not only are the figures uncouth, and the origin often frivolous, but the boundaries are not distinct. Stars occur under different names; while one constellation encroaches upon another. Though,

* This means a of Aries, ẞ of Lyra; the genitive case in Latin being equivalent to the preposition of.

Chambers well remarks, " Aries should not have a horn in Pisces and a leg in Cetus, nor should 13 Argôs pass through the Unicorn's flank into the Little Dog. 51 Camelopardali might with propriety be extracted from the eye of Auriga, and the ribs of Aquarius released from 46 Capricorni."

however, the constellations are thus rude and imperfect, there seems little hope of any change. Age gives them a dignity that insures their perpetuation.

The Invention of the Constellations goes back into ages of which no record remains. By some it has been ascribed to the Greeks. When the signs of the zodiac were named, they doubtless coincided with the constellations. Aries (the ram) was so called because it rose with the sun in the spring-time, and the Chaldean shepherds named it from the flocks, their most valued possession. Then followed, in order, Taurus (the bull) and Gemini (the twins), called from the herds, which were esteemed next in value. At the summer solstice, the sun appears to stop, and, crab-like, to crawl backward; hence the name Cancer (the crab). When the sun is in Leo, the brooks being dry, the lion leaves his lurkingplace and becomes a terror to all. Virgo comes next, when the virgins glean in the summer harvest. At the autumnal equinox, the days and nights are equally balanced, and this is beautifully represented by Libra (the scales). The vegetation decays in the fall, causing sickness and death; the Scorpion, which stings as it recedes, is suggestive of this Parthian warfare. Sagittarius (the archer) tells of the hunting month. Capricornus (the goat, which delights in climbing lofty precipices) denotes how at the winter solstice the sun begins to climb the sky on his return north. Aquarius (the water-bearer) is a natural emblem of the rainy season, Pisces (the fishes) is the month for fishing.