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valuable to all institutions having an equatorial telescope. Indeed, they greatly enhance the value of the work for all classes of students.
4. Several small constellations that were delineated on the maps, but were not described in former editions of the book, have been described, and their history given in the present edition.
5. The page of the book has been greatly enlarged, for the double purpose of printing more matter and in larger type; and to afford scope for wood-cut illustrations. Of these, great numbers have been introduced into the second part of the work, adapting it, in this respect also, to the wants of both teacher and student.
6. Still further to illustrate the second part of the work, the first map of the atlas has been re-drawn and re-engraved, so as to illustrate more and better than the old map.
7. Two entirely new map have been introduced into the Atlas, containing views of eighty different celestial objects; such as Double Stars, Clusters, Nebulæ, Comets, &c. These are all referred to in the book, and in turn refer from the objects back to the page of the book where they are described. These maps and the corresponding descriptions in the book will be found not only extremely interesting, but of incalculable value to the student.
8. A chapter on the history, structure and use of Telescopes, Transit Instruments, &c., has been introduced-a subject which every student of astronomy should understand, but one to which no attention was given in the previous editions.
Such are some of the principal new features of the present edition-larger type, new questions, telescopic objects, new maps, new matter, and numerous illustrations, making it the most perfect and complete text-book of astronomy ever offered to the American public.
New York, April, 1856.
CHAPTER I. General Phenomena of the Solar System, History, &c.,
1. ASTRONOMY is the science of the heavenly bodies—the Sun, Moon, Planets, Comets, and Fixed Stars.
2. In entering upon this study, the phenomena of the heavens, as they appear on a clear evening, are the first objects that demand our attention. Our first step is to learn the names and positions of the heavenly bodies, so that we can identify, and distinguish them from each other.
In this manner they were observed and studied ages before books were written, and it was only after many careful and repeated observations, that systems and theories of Astronomy were formed. To the visible heavens, then, the attention of the pupil should be first directed, for it is only when he shall have become, in some measure, familiar with them, that he will be able to locate his Astronomical knowledge, or fully compre
hend the terms of the science.
3. For the sake of convenient reference, the heavens were early divided into constellations, and particular names assigned to the constellations and to the stars which they contain. A constellation may be defined to be a cluster or group of stars embraced in the outline of some figure. These figures are, in many cases, creations of the imagination; but in others, the stars are in reality so arranged as to form figures which have some resemblance to the objects whose names have been assigned to them.
These divisions of the celestial sphere bear a striking analogy to the civil divisions of the globe. The constellations answer to states and kingdoms, the most brilliant clusters to towns and cities, and the number of stars in each, to their respective population. The pupil can trace the boundaries of any constellation, and name all its stars, one by one, as readily as he can trace the boundaries of a state, or name the towns and cities from a map of New England. In this sense, there may be truly said to be a Geography of the Heavens.
4. The stars are considered as forming, with reference to
1. What is Astronomy? 2. What first studied? First step? 8. How are the heavens divided, and why? What is a constellation? What of these figures? In what sense may there really be a "Geography of the heavens !" 4. How are the stars classified, as respects their magnitudes? What expedient for designating their places in the heavens?
their magnitudes, sixteen classes; the brightest being called stars of the first magnitude, the next brightest, stars of the second magnitude, and so on to the sixth class, which consists of the smallest stars visible to the naked eye. The next ten classes are seen only through telescopes.
In order to be able to designate with precision their situations, imaginary circles have been considered as drawn in the heavens, most of which correspond to, and are in the same plane with, similar circles, supposed for similar purposes, to be drawn
on the surface of the Earth.
5. In order to facilitate the study of Astronomy, artificial representations of the heavens, similar to those of the surface of the Earth, have been made. Thus, a Celestial Atlas, composed of several maps, accompanies this work. Before, however, proceeding to explain its use, it is necessary to make the pupil acquainted with the imaginary circles alluded to, called the Circles of the Sphere.
CIRCLES OF THE SPHERE.
6. The Axis of the Earth is an imaginary line, passing through its centre, north and south, about which its diurnal revolution is performed.
The Poles of the Earth are the extremities of its axis.
The Axis of the Heavens is the axis of the Earth produced both ways to the concave surface of the heavens.
The Poles of the Heavens are the extremities of their axis.
The Equator of the Earth is an imaginary great circle passing round the Earth, east and west, everywhere equally distant from the poles, and dividing it into northern and southern hemispheres.
The Equator of the Heavens, or Equinoctial, is the great circle formed on the concave surface of the heavens, by producing the plane of the Earth's equator.
A plane is that which has surface but not thickness. The plane of a circle is that imaginary superficies which is bounded by the circle.
7. The Rational Horizon is an imaginary great circle, whose plane, passing through the centre of the Earth, divides the heavens into two hemispheres, of which the upper one is called the
5. What helps to facilitate the study of the heavens? Circles? Cailed what? 6. Axis of the Earth? Poles? Axis of the heavens? Poles of the heavens? Equator of the Earth? Equator of the heavens, or Equinoctial? 7. Rational horizon? Sensi
ble or apparent?