Of these stars, Dr. Herschel remarks that from 15,000 to 20,000 of the first seven magnitudes are already regis tered, or noted down in catalogues; and Prof. Olmsted observes that Lalande has registered the positions of no less than 50,000.

349. The reason why there are so many more of the small stars than of the large ones is, that we are in the midst of a great cluster, with but few stars near us, the number increasing as the

circumference

of Our view is enlarged. (See second cut, page 28, and also the adjoining.)

Let the central star represent the sun (a star only among the rest), with the solar system revolving between him and the first circle. The 18 stars in space 1st will appear to be of the first magnitude, on a count of their nearness, and they are thus few because they embrace but a small part of the entire cluster. The stars of space 24 will appear smaller, being more distant; but as it embraces more space, they will be more numerous. Thus as we advance from one circle to another, the apparent magnitude constantly diminishes, but the number constantly increases. The large white circle marks the limit of our

NUMBER OF STARS OF EACH MAGNITUDE.

natural vision. Even this cut fails to present fully to the eye the cause of the rapid increase in numbers, for we can only show the surface of a cut section of our firmament of stars, which exhibits the increase in a plane only; whereas our sun seems to be im. bedded in the midst of a magnificent cluster (like a single apple in the midst of a large tree richly laden with fruit), the stars of which we view around us in every direction.

349. Why so many more of small stars than of the larger? (Illustrate by diagram. Does this convey a complete idea of the position of the sun, with reference to the fixed stars? Why not? What does his position more nearly rusemblo ?)

350. If we suppose that each of these suns is accompanied only by as many planets as are embraced in our solar system, we have nine thousand millions of worlds in our firmament. No human mind can forin a conception of this number; but even these, as will hereafter be shown, form but a minute and comparatively insignifi cant portion of the boundless empire which the Creator has reared, and over which he reigns. "Lo, these are parts of his ways; but how little a portion is heard of Him? but the thunder of his power who can understand." (Job xxvi. 14.)

DISTANCES AND MAGNITUDES OF THE STARS.

351. It has been demonstrated that the nearest of the fixed stars cannot be less than 20,000,000,000 (twenty billions) of miles distant! For light to travel over this space, at the rate of 200,000 miles per second, would require 100,000,000 seconds, or upwards of three years.

What, then, must be the distances of the telescopic stars, of the 10th and 12th magnitudes? "If we admit," says Dr. Herschel, "that the light of a star of each mag nitude is half that of the magnitude next above it, it will follow that a star of the first magnitude will require to be removed to 362 times its distance, to appear no larger than one of the twelfth magnitude. It follows, therefore, that among the countless multitude of such stars, visible in telescopes, there must be many whose light has taken at least a thousand years to reach us; and that when we observe their places, and note their changes, we are, in fact, reading only their history of a thousand years' date, thus wonderfully recorded." Should such a star be struck out of existence now, its light would continue to stream upon us for a thousand years to come; and should a new star be created in those distant regions, a thousand years must pass away before its light could reach the solar system, to apprise us of its existence.

850. What supposition and conclusion? Scripture quotation?

$51. Distances of the nearest stars? Time for light to travel over thus spaco? Suppositions and conclusions of Dr. Herschol?

352. From what we have already said respecting the almost inconceivable distances of the fixed stars, it will readily be inferred that they must be bodies of great magnitude, in order to be visible to us upon the earth. It is probable, however, that "one star differeth from another" in its intrinsic splendor or "glory," although we are not to infer that a star is comparatively small be cause it appears small to us.

353. The prevailing opinion among astronomers is, that what we call the fixed stars are so many suns and centers of other systems. From a series of experiments upon the light received by us from Sirius, the nearest of (the fixed stars, it is concluded that if the sun were removed 141,400 times his present distance from us, or to a point thirteen billions of miles distant, his light would be no stronger than that of Sirius; and as Sirius is more than twenty billions of miles distant, he must, in intrinsic magnitude and splendor, be equal to two suns like ours. Dr. Wollaston, as cited by Dr. Herschel, concludes that this star must be equal in intrinsic light to nearly fourteen suns. According to the measurements of Sir Wm. Herschel, the diameter of the star Vega in the Lyre is 38 times that of the sun, and its solid contents 54,872 times greater! The star numbered 61 in the Swan is estimated to be 200,000,000 miles in diameter.

66

354. Sir John Herschel states, that while making observations with his forty-feet reflector, a star of the first magnitude was unintentionally brought into the field of view. Sirius," says he, "announced his approach like the dawn of day;" and so great was his splendor when thus viewed, and so strong was his light, that the great astronomer was actually driven from the eye-piece of his telescope by it, as if the sun himself had suddenly burst upon his view.

352. What inference from the great distance of the stars? What proba bility as to the real magnitude the stars?

353. The prevailing opinion among astronomers? Conclusions from experiments with Sirius? Magnitude of Vega? Of No. 61 in the Swan?

354. Incident stated by Dr. Herschel (Relative light of the stars of the first six magnitudes ?)

According to Sir Wm. Herschel, the relative light of the stars of the first six magnitudes is as follows:

355. ALTHOUGH this work is designed particularly to illustrate the mechanism of the heavens, as displayed in the solar system, we are desirous of furnishing the learner with a sufficient guide to enable him to extend his inquiries and investigations not only to the different classes of bodies lying beyond the limits of the solar system in the far off heavens, but also to the constellations, as such. For this purpose, we shall here furnish a brief description of the principal constellations visible in the United States, or in north latitude; by the aid of which, the student will be able to trace them, with very little difficulty, upon that glorious celestial atlas which the Almighty has spread out before us.

If the student will be at the trouble to identify the constellations by the aid of these descriptions, and without the aid of charts, it will give him a practical familiarity with the heavens which can be acquired in no other way. Indeed, this exercise is indispensable to a competent knowledge of sidereal astronomy, even where maps of the constellations are used. Let all students, therefore, embrace every favorable opportunity for looking up the constellations.

Those who wish to study their mythological history will consult the author's edition of the "Geography of the Heavens," by E. H. Burritt-the most reliable and popular work upon this subject in the English language.

356. Of the nature and origin of the constellations we have already spoken, at 343. Their formation has been the work of ages. Some of them were known at least 3,000 years ago. In the 9th chapter of Job, we

355. Principal design of this text-book? done for this purpose? (Substance of note?)

What further object? What

356. What said of the formation of the constellations? Antiquity Scripture allusions?

read of "Arcturus, Orion, and Pleiades, and the chambers of the south ;" and in the 38th chapter of the same book, it is asked, "Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion? Canst thou bring forth Mazzaroth in his season? or canst thou guide Arcturus with his sons?"

357. The constellations are divided into ancient and modern. According to Ptolemy's catalogue, the ancients had only 48 constellations; but being found convenient in the study of the heavens, new ones were added to the list, composed of stars not yet made up into hydras and dragons, till there are now scarcely stars or room enough left to construct the smallest new constellation, in all the spacious heavens. The present number, according to the catalogue of the Observatory Royal of Paris, is 93.

358. The constellations are further divided into the Zodiacal, Northern, and Southern. The zodiacal constellations are those which lie in the sun's apparent path, or along the line of the zodiac. The northern are those which are situated between the zodiacal and the north pole of the heavens; and the southern, those which lie between the zodiacal and the south pole of the heavens. They are distributed as follows-viz., 12 zodiacal, 35 northern, and 46 southern.

This division is convenient for reference; but in tracing the constellations in the heavens, or upon a map, it is better to begin with those that are on or near the meridian, and proceed eastward, taking northern and southern together, so far as they are view. And where classes in astronomy are organized during the fall months, it will be found advantageous to begin with the constellations that are in view at seasonable hours during those months.

359. In consequence of the eastward motion of the earth in its annual revolution, the constellations rise earlier and earlier every night; so that if an observer were to watch the stars from the same position for a whole year, he would see each constellation, in turn, coming to the meridian at midnight (or at any other hour fixed

357. How are the constellations classified? How many of eacn? In all? 858. How further classified? Describe each. How many of each? (What said in note?)

359. What said of the rising of the constellations? How proceed in de scribing and tracing?