PREFA C E. IT has long been my opinion that an Atlas of the Heavenly Bodies, uniform in size and style, would form a useful and appropriate addition to my series of Elementary Works on Physical, Classical, and General Geography-an opinion confirmed by many communications from the heads of educational establishments, and others interested in the progress of knowledge. An assurance of the want of a work of the kind led to inquiry as to whether any such existed, and to the conviction that no one, combining elementary facts with scientific precision, had been placed within the reach of the public; hence the only course open to me was to project a new work, suited, as far as possible, to the felt exigency. The subject of each Illustration has been carefully studied, and the details have been worked out at such an expense of time and labour as is seldom bestowed on an elementary work. In illustration of this, it may be noticed that, in the concluding six Maps, the position of every star has been calculated, and its place projected, from the Catalogue prepared under the direction of the British Association for the Advancement of Science, so that the results of that elaborate work are here first produced in a graphic form. It is hoped, therefore, that this Atlas will not only prove useful as an Introduction to Astronomy, but that it will commend itself to the more advanced cultivators of the science. In the present edition three Illustrations appear for the first time-Plate 13, Meteors; 14, Spectrum Analysis applied to the Sun and Stars; and 21, Ecliptic Charts, representing the apparent paths of the planets Venus, Mars, &c. Plates 4, 5, 9, and 12 have been re-engraved from new drawings, and the others have been brought up to the present state of knowledge. The text comprises, in a condensed form, an elementary Survey of the Heavens, in which each figure in the Plates is popularly explained, and the latest facts of the science are presented. This part of the work is due to Professor Grant, of the Glasgow Observatory. I take this opportunity of returning grateful thanks to Warren De La Rue, Esq., F.R.S., formerly President of the Royal Astronomical Society of London, who placed at my disposal a valuable series of original photographs, from which many of the new drawings were made; and also to Padre Secchi, the eminent Director of the Observatory of the Collegio Romano, for the instructive photographs representing the Phases of the Moon in Plate 4. A. KEITH JOHNSTON. EDINBURGH, December 1868. ATLAS OF ASTRONOMY. ELEMENTARY SURVEY OF THE HEAVENS. CHAPTER I. General Aspect of the Stellar Heavens-First Results of Observation— THE heavens, if viewed on a fine night when the sky is free of clouds, present the aspect of an immense hemispherical vault, the concave surface of which is studded with a countless number of luminaries of different degrees of brightness. If the phenomenon be observed for a few hours, it will be found that the stars, like the sun and moon, have a general movement from east to west, ascending above the horizon at different points in the east, and setting beneath the horizon at corresponding points in the west. Like the sun and moon also, the stars attain their highest position above the horizon when they are due south, or on the meridian. If observations of this kind be prosecuted for several successive nights, it will be found that the stars which sink beneath the horizon in the west reappear on the following night above the horizon in the east, and that the interval of time which elapses between two consecutive appearances of a star in the east, or two consecutive disappearances in the west, is in all cases exactly the same; and this is true in regard to the time which elapses between two consecutive returns of the star to the meridian, or any other determinate point of its course above the horizon. The interval of time in all such cases is, in round numbers, twenty-four hours, as shown by an ordinary clock or watch. An interesting question which here offers itself is this, What is the time during which a star remains visible above the horizon? The results of observation are in this instance clear and precise. The stars which rise due east set due west, and remain above the horizon twelve hours. The stars which rise to the south of due east, set at corresponding points to the south of due west, and, supposing the observer to be situate anywhere in the northern hemisphere, remain visible above the horizon during less than twelve hours, the interval of visibility gradually diminishing the more nearly the star rises towards the south. Finally, the stars which rise to the north of due east, set at corresponding points to the north of due west, and dwell above the horizon during a longer period than twelve hours. It a |