Paper VI. 1. Dec. 11, 1868: A.M. at ship; long. 52° 12′ E.: observed meridian altitude 75° 40' 10": zenith S. of eye 20 feet: required the latitude. 2. Dec. 15, 1868: long. 30° 15 W.: at 9h 10m P.M. mean time at ship the observed altitude of Polaris off the meridian being 56° 20′ 30′′: index error -1' 2": eye 19 feet: required the latitude. : 3. Dec. 12, 1868: lat. by account 52° 26′ S. : long. 106°37′E. : the following double altitude of the sun was observed : app. time at ship. 4 30 30. P.M. obs. alt. O's 1.1. 56° 39′ 49′′ bearing N.W. N. 31 27 23 eye 19 feet: course and distance in the interval N.by E.E. 28 miles : required the latitude when the second observation was taken. 4. Verify No. 3, by Sumner's method. 5. Dec. 9, 1868: lat. 48° 52' N.: long. 144° 46′ E.: equal altitudes of being observed when the corresponding times by chronometer were 84 20h 12m 42s and 8a 22h 30m 46s: required the error of the chronometer for apparent and mean time at the place of observation, and also on mean time at Greenwich. 6. Nov. 22, 1868: P.M. at ship: lat. 5° 20' N.: time by chrometer 4h 22m 17s, which was supposed to be 2m 17s fast on mean time at Greenwich, a Aquila E. of meridian. obs, alt. a Aquila. 70° 47' 4" obs. alt's ul. obs. dist. a Aquila and (n.l. eye 20 feet required the longitude by lunar, and the error of chronometer on mean time Greenwich. 7. Nov. 17, 1868: the observed meridian altitude of the in an artificial horizon being 79° 46′ 30′′: index error -1′16′′: required the true altitude of sun's centre. 8. At noon a ship by account is in lat. 38° 15′ N., long. 63° 30′ W., but by observation she is in lat. 38° 45' N., long. 63° 16′ W., being evidently in a current, required its set, drift, and rate per hour, during the last 24 hours. GREAT CIRCLE SAILING. 1. If, on a Mercator's Chart, any two places, (not on the equator, nor on the same meridian) be selected, we see that the shortest distance between them is a straight line, and providing no land intervene, and the winds and currents are favourable for the purpose, the navigator has no occasion to change the course on which he starts, in order to sail from the one to the other. 2. On a terrestrial globe, apply a piece of thread (stretching it evenly) to the same two places, and it will then be seen, that the shortest distance between them is not on a straight line, but on a portion of a circle, and in order to arrive at either place from the other, by such a route, the course to be sailed must be constantly varying. (a.) When both places are on the equator or on the same meridian, the track on the great circle and that on the rhumb line are the same, and the course will be N., S., E., or W., according to the relative position of the ports. 3. Now the Earth is an oblate spheroid, or sphere of revolution, and the small difference between the equatorial and polar diameters does not preclude our regarding it as a perfect sphere in numerous computations. 4. If a sphere be cut in any direction by a plane, the section must be a circle. (a.) If the plane pass through the centre of the sphere, we : 5. Two great circles always intersect in two points at the distance of a semicircle from each other. (a.) The equator, which is a great circle, bisects every other great circle on the earth's surface, and there must necessarily be two points in every such circle, equi-distant from the equator, and at the same time furthest removed from it: each of these points is called "Vertex;" and the "Latitude of Vertex," which is the highest latitude attained in sailing on a Great Circle, is the nearest approach to the elevated pole. The meridian cutting the great circle at right angles, and dividing it into quadrants, is called the "Meridian of Vertex;" and the "Longitude from Vertex," is the arc of the equator intercepted between the meridian of any place and the meridian of Vertex 6. The arc of a great circle joining two points, is the shortest distance between them on the surface of a sphere. (a.) The same great circle cannot be drawn through more than two points, selected at random on the surface of a sphere. 7. A spherical triangle is the portion of space on the surface of a sphere, included between three arcs of intersecting great circles. All the computations for Great Circle Sailing are performed by Spherical Trigonometry. 8. The configuration of the earth is truly represented on Mercator's Chart only at the equator, every where else it is distorted the great circle track between any two places, drawn on such a chart, instead of appearing (as it really is,) the shortest, would be represented as a curved line. It is impossible, under any circumstances, to sail a ship on the true great circle track, but a very close approximation may be made to it in some latitudes; and moreover a knowledge of Great Circle Sailing is very useful in all latitudes, for when adverse winds are encountered, it teaches on which tack to lay the ship, in order to arrive most speedily at her destination. These few observations will suffice, since it is not required to enter into calculations, and it is necessary to be provided with Towson's "Tables to facilitate the Practice of Great Circle Sailing," at the end of which will be found explanations as to their use, as well as the linear index which accompanies them. GREAT CIRCLE TRACKS AND DISTANCES, AND AZIMUTHS WITHOUT CALCULATION. Mr. RUSSEL has supplied Diagrams of Great Circle Sailing, (published by Mrs. TAYLOR, of the Nautical Academy, in the Minories,) by which the science becomes little more than a mechanical operation, and which relieves it of all the difficulty of abstruse calculation. On Mr. RUSSEL's sheet, there is with a Spherical Diagram, a Mercator's Chart,—to facilitate the finding of the Great Circle, and the distance between any two given places. The principles on which the Diagram is constructed may be easily understood; for, as every Great Circle cuts the Equator in two points diametrically opposite, it follows that a series of great circles drawn through a given point in the Equator, in every possible direction, will all meet at another point in it, 180° distant from the former. Any person accustomed to navigate his ship by Great Circle Sailing, will readily understand the nature and advantages of Mr. Russel's plan, and we recommend it to the attention of commanders of vessels, who are bound on distant voyages. Vide Shipping Gazette, March 18, 1853. LAW OF STORMS. BY WILLIAM RADCLIFF BIRT, F.R.A.S. Author of the Article on " Atmospheric Waves," in the Admiralty Manual of Scientific Enquiry; "The Hurricane," and "Sailor's Guides;" "Hand Book of the Law of Storms," Etc, Etc The object of the following remarks on Revolving Storms, is to exhibit the importance of gaining such a knowledge of the "Law of Storms," that the commander of a vessel may know instinctively what part of a cyclone he may be in; for this, nothing more is requisite, than that he possess a competent knowledge of the bearing of the centre from the ship, as determined by the direction of the wind, and the result of the hauling of the wind with or against the sun, as indicating on which side of the axis line he may be placed, the axis line coinciding with the path of the centre; with this knowledge all instruments may be dispensed with, except the barometer. 1. Within the last 30 years the assiduity of meteorologists has developed a most important and highly interesting department of meteorology. This department has immediate reference to, and must exert a most beneficial influence on the Commercial and Maritime interests of the Country. It is now popularly known as the Law of Storms, and on no class of men can the study of it tell with more effect, than on the mercantile marine; not that Her Majesty's Navy stands less in need of the important knowledge contributed by an investigation of storms, but the education of its officers fits them more readily to appreciate and apply such knowledge, when overtaken by a hurricane or cyclone. 2. The primary idea or fundamental notion of a cyclone, is that of a vast body of air in a state of rotation, more or less |