ANNUAL REVOLUTION OF THE EARTH ROUND THE SUN, PHASES AND MOVEMENTS OF THE MOON ROUND THE EARTH, MAP OF THE MOON, REDUCED FROM THE LARGE MAP OF MM. BAER AND MADLER, 559 Crich-hill, Derbyshire, Section of the Jura Mountains, Association of Stratified and Unstratified Rocks, 631-633 Ben Lomond, from the Lake, Aiguille de Dru, Disintegrated Granite, Granite Veins, Serpentine, Positions of Trap, Basalts, Grotte des Fromages, Porphyry, Needle Rocks, Isle of Wight, Initial Letter, Gneiss System, . Mica-schist System, Mount Taygetus, from the Plains of Sparta, Skiddaw Mountains, Fossils from Snowdon, Nereites Cambrensis, Initial Letter-The Bone Well, Ludlow, Hills near Brecon, Silurian System of Rocks, Vale of the Towy, Eye of the Trilobite, The Stiper Stones, Terebratulæ, Old Lincoln Quarry, near Iron Bridge, Euomphala, Wenlock Limestone, Ludlow Corals, Wenlock Corals, Remains of Fishes, . Palmer's Cairns, Ludlow, Initial Letter-Trap Dyke, Brockhill, Worcester, Old Red Sandstone, near Bristol Channel, Vegetable Remains in Old Red Sandstone, Tails of the Shark, Trout, and Wrasse, Scales on head of Cephalaspis, Coccosteus cuspidatus, Pterichthys, Initial Letter-Carboniferous System, Mountain Limestone, Section of the Crich-hill, Encrinal Limestone, Orthoceras lateralis, and Bellerophon costatus, Teeth of the Hybodants and Megalichthys, Projection of Millstone Grit, Section of the Bristol Coal-field, Fault in Coal-field, Imaginary section before disturbance, Section after disturbance, Seam dipping, Page 628 630 634 638 640 640 640 640 641 641 641 643 644 646 647 648 649-650 652 653 656 657 658 659 660 663 666 667 667 669 671 671 672 673 674 675 675 676 678 678 679 680 681 684 €85 €86 687 687 688 690 691 692 693 C93 094 695 698 698 699 699 700 Various Tail-pieces, Vignettes, &c. 7002 710 713 714 714 715 716 717 719 719 720 721 724 726 726 729 731 732 754 759 761 761 762 Broken Ledges of Slate, 763 Strata smoothed and striated by Drift, 764 Diluvial Formations seen from the Acropolis at Athens, 765 766 Corals, . Coast of Northern Greece, from the Gulf of Corinth, Temple of Jupiter Serapis, Section of a Terraced Valley, . Chart and View of the Isle of Palma, Crater of Vesuvius in 1829, 733 733 735 736 737 738 741 742 744 745 746 748 748 750 751 752 766 768 773 774 777 779, 780 781 782 783 784 788 DESCRIPTION AND USE OF THE SIDEREAL MAPS. THESE Maps have been constructed to show the sidereal hemisphere visible on the parallel of Greenwich, and being also adapted to the meridian of Greenwich, they are drawn on the plane of that horizon. To insure the greatest amount of accuracy, the stereographic projection has been made use of, because of all projections that occasions the least possible disarrangement of the relative position of the stars and of the angles they form one with another. There is a difficulty in reducing a concave surface to a plane without distortion taking place somewhere, and in the projection here adopted a little compression will be found, gradually increasing from the horizon to the centre of the map. The constellations when at or near the zenith, will be found to be somewhat smaller than when at the extremities of the projection or near the horizon. Three, four, or five stars may appear in the heavens so as to form a group, and present to the observer the appearance of a triangle, a rhomboid, trapezium, or parallelogram, which figures are more correctly preserved by this projection than by any other which might have been made use of. The difference between celestial and terrestrial maps should not be lost sight of. When a comparative observation is made between one of these maps and the heavens at any of the times given on the next page, the map should be held up in a vertical position, placing that part of the map downwards towards which the observer is directing his attention. For instance, if the stars in the south are to be examined, the person's face must be turned that way, with the south or bottom of the map downwards; if for the north, the map must be reversed, with the north or top of the map downwards, when a complete view of the heavens in either of those directions will be obtained. If for the east and west, the sides of the map are to be similarly held, corresponding with the aspect required. The centre of each map represents the zenith, that part of the heavens which is exactly over the observer's head, and will answer equally well for any other place upon the same parallel of latitude, making the allowance of four minutes for each degree, east or west, sooner or later; which shows that all persons living on the same parallel of latitude have in succession the same view of the starry concave. Another appearance would be presented if the observer were at either of the poles. Supposing there were inhabitants at the North Pole, to them one half of the firmament would never set, and the other half would never rise. The polar star would be their zenith, and appear quite stationary, with all the other stars in view revolving round it in circles. To such inhabitants the equator would be the horizon, and at whatever elevation a star was first seen in their winter, there it would remain, and appear to complete a circle at that elevation once in every twenty-four hours. If there were inhabitants at the South Pole, they would be similarly situated with regard to stars in the southern hemisphere; they would never see the stars on the north side of the equator or northern hemisphere, nor would those in the southern hemisphere ever set to them. To the inhabitants of the equator, the whole of the stars from pole to pole, rise and set perpendicularly to their horizon once in every twenty-four hours. As the equator has no parallel of latitude, so has its zenith no declination, because the celestial equator passes immediately over it in a line from east to west. If an observer moves towards either pole from the equator; for every degree of his progress his zenith will have just so many degrees of declination, and as many degrees can he see beyond the pole towards which he is advancing, and he will lose sight of the pole from which he is receding in the same proportion. For example, as the inhabitants of London are situated 510 from the equator northwards, their zenith is 51° elevated above the celestial equator. As 510 is the distance from the zenith to the equator, it follows that 3810 must be seen by an inhabitant of London below the equator to make up the complement of the quadrant, or 90°. Between the zenith and the pole will be found 3840, requiring 510 beyond the pole to complete the other quadrant of 90°, thus together completing the hemisphere of 180°. With these preliminary explanations a few words will explain the use of the maps. Each map may be supposed to represent the heavens at the hours named. The dotted circle crossing |
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