1. To represent the Motions of the Equinoctial Points back- ibid. 11. To illustrate the Equation of Time, &c. 12. To find the right Ascension, &c. of a Star... the Latitude and Longitude of a Star.... ibid. the Place of a Star on the Globe by, &c....... 337 at what Hour a given Star transits the Meri. 16. On what Day a Star will come to the Meridian 17. To represent the Face of the Heavens for any given day ibid. ibid. 18. To trace the Circles of the Sphere in the Heavens 19. To find the Circle of perpetual Apparition.......... 346 ibid. 354 .... the Hour, the Latitude and Azimuth given 44. To illustrate the Harvest Moon.... 45. To find the Azimuth of the Moon, and thence High 49. To find the Time of a Comet's Rising, &c....om ibid. 50. To find the same at London...... 986 An Introduction to Practical Astronomy, in which is intro- duced a variety of curious Problems, from..... 435 to the end of the Work. ASTRONOMICAL ESSAY S. ESSAY I. PART I MANKIND have in all ages been desirous of forming rational conceptions of the nature and motion of those bodies that appear in the vast concave above their heads. Amidst the infinite variety of objects which surround them on every side, the heavenly bodies must have been amongst those which first attracted their attention. They are of all objects the most conspicuous, the most important, and the most beautiful. Astronomy instructs us in the laws, or rules, that govern and direct the motions of the heavenly host. It weighs and considers the powers by which they circulate in their orbs. It enables us to discover their size, determine their distance, explain their various phenomena, and correct the fallacies of the senses by the light of truth. A Astronomy is not merely a speculative science; its use is as extensive as its researches are sublime. Navigation owns it for its guide; by it, commerce has been extended and geography improved. It is astronomical observations that form the basis of geography. Thus, it has co-operated with other causes in the greatest of all works, the diffusion of knowledge and the civilization of man. As, in order to attain an accurate idea of any piece of mechanism, it is best to begin our investigation by an examination of those parts which give motion to the rest, the primary causes of those effects for which the machine was made ; so the young pupik will more easily gain a just idea of the motion of the heavenly bodies, by considering them as seen from the sun, the centre of our system, and the principal agent used by the LORD OF NATURE for conducting and regulating the planetary system. It will not be difficult, after this, to inform him how those appearances are to be accounted for, that arise from his particular situation; whence he views the heavens from a point which is not in the centre of the system, and is consequently the source of many apparent irregularities. This knowledge attained, it will be easy to prove to him, that the real and apparent motions of the heavenly bodies are frequently the reverse of each other. For, being by this means put into possession of the universals of this science, the knowledge of particulars will be rendered facile and clear. |