astronomer owes to navigation the best practical illustration of the utility of his pursuits, and the gratifying conviction that the labours of his predecessors, in the career of fame, have conferred a real benefit on mankind. The principal English Treatises on the subject of Navigation itself are, Robertson's Elements of Navigation; Riddle's Treatise on Navigation and Nautical Astronomy; Professor Inman's Treatise on Navigation and Nautical Astronomy; Kerrigan's Young Navigator's Guide to the Sidereal and Planetary Parts of Nautical Astronomy; Norie's Complete Epitome of Practical Navigation; Bowditch's Improved Practical Navigator, edited by Kirby; and Moore's Practical Naviga tor. The works on subjects connected with Navigation are far too numerous for insertion here: we may mention, however, Dr. Maskelyne's Preface to the Nautical Almanac, and the Preface to Taylor's Logarithms by the same author. Some additions to the Nautical Almanacs of different years by Maskelyne, Wales, Campbell, Lyons, Witchell, Blair, and Brinkley; Lax's Tables to be used with the Nautical Almanac, &c.; the Nautical Almanac; Connoissance des Tems; Professor Schumacher's Ephemeris, &c.; Thomson's Lunar and Horary Tables; Workman's Navigation Improved; Investigations relative to the problem for clearing the Apparent Distance, &c. by Dr. Brinkley, in the Gentleman's Mathematical Companion for the Year 1815; Mendoza's Paper in the Philosophical Transactions for 1797; Kelly's Practical Introduction to Spherics and Nautical Astronomy; Barlow's Essay on Magnetic Attractions; Bain, on the Compass; Several valuable Papers in the Philosophical Transactions by Halley, Maclaurin, Kater, Sabine, Foster, &c. &c. The foreign authors on Navigation are also very numerous, the modern treatises are, Bezout, Traité de Navigation, and Dubourguet, Traité de Navigation: the more ancient are those of Bartolomew Crescenti, Rome, 1607; John Baptist Riccioli, Bologna, 1661, &c. &c.; and that of M. Peter Bouguer, 1760, abridged and improved by M. de la Caille. TABLE I. Logarithmic Sines, Tangents, and Secants, to every Point and Quarter Point of the Compass. 34 3 34 4 3 9.744739 9.919846 9.824893 10.175107 10.080154 10.255261 10.111815 10.197641 544 ** 4 NAVIGATION TABLE II. A Table of Corrections to be added to the Mean Middle Latitude to find the True Middle Latitude. When the difference of latitude is under 20, the correction may be neglected; when it is 2° and under 30, add EXPLANATION OF SCIENTIFIC TERMS MADE USE OF IN THIS VOLUME. N.B. Many of the terms are common to this and the two preceding volumes; but those explanations that were given in the former Glossaries will be merely referred to in the present, except in a few cases, where the definitions were not supposed to be sufficiently explicit. Several omissions may be supplied by consulting the Indexes. ABERRATION. The name given to an apparent change of place in the fixed stars, consequent upon the time taken up during the passage of a ray of light to the eye compared with that of the earth's annual motion. This is familiarly explained in the preceding glossaries, and more scientifically in the present volume :-Astronomy, pages 64 and 146, and History of Astronomy, page 89. ACCELERATION OF MOTION.-See Glossary I. Acceleration may be either regular or variable, that is, by equal or by unequal accessions in equal times. The motions of the planets are continually accelerated, according to a known law, from their aphelion to their perihelion; while there is a continued retardation in a like ratio in the opposite half of their orbits: the average of these motions through the whole circuit (the space divided by the time) is called the mean motion. ACOTYLEDONOUS.-See Cotyledon. ACRONYCAL (a Greek compound denoting the point of night) in its literal acceptation denotes the moment of the sun's setting or of his rising, the beginning or the end of night. In modern astronomy it is confined to the former; and a star is said to rise or to set acronically when it rises or sets at the instant of sunset. On the contrary, when a star rises or sets in the morning at the moment of sunrise, it is said to rise or to set cosmically; but how this Greek derivative has been so applied we have not been able to determine. In the case of its cosmical rising or setting, the star is never visible; but when it appears in the morning a little before the sun, or sets in the evening a little after him, it is said to rise or to set heliacally (Greek helios, the sun); and it is only in his heliacal rising or setting, that the planet Mercury is ever visible to the naked eye. ALMANAC.-See Calendar. The word is Arabic, signifying the reckoning. ALTITUDE of the sun, or of a star.-See Glossary II., article Horizon; and AstroAMPLITUDE of the sun, or of a star.nomy, page 16. See Glossary II., article Horizon; Astronomy, page 256; and Navigation, page ANGLE.-See Glossary I. 30. -OF ELONGATION.-See Elon gation. ANNULAR, an adjective, from the Latin ANNUAL PARALLAX-See Parallax. annulus, a ring. Those eclipses of the sun, in which a ring of light is visible around the dark body of the moon, are termed Annular Eclipses; they are also Central Eclipses, because the centres of the sun and of the moon appear to coincide. ANTARCTIC.-See Arctic. APPARENT TIME.-See Time. ARC OF A CIRCLE.-See Glossary I. the spherical concavity of the sky; and will mark two points in the heavens that are also called the north and the south poles, around which, or rather their line of junction, all the fixed stars appear to revolve. The north pole of the heavens (the only one visible in our latitude) is a point, situated in the constellation called Ursa Minor, or the little bear; and a bright star, in the tip of the tail of this imaginary animal, is called the Pole-star, or Polarstar, because near to the real pole. cles supposed to be drawn round the Arctic, and the Antarctic pole, at the distance of about 234 degrees, are termed, respectively, the Arctic and the Antarctic Circle. On the terrestrial globe, those circles surround what are called the two Frozen Zones, or girdles of the earth. AREA. See Glossary II. ASCENSION, RIGHT.-See Right As cension. Cir ASTRONOMICAL HORIZON.-See Glossary II., Horizon. ATMOSPHERE.-See Glossary I. REFRACTION OF. See Glossary II. ATTRACTION-See Glossary I. AXIS. See Arctic, and Astronomy, page 6. OF AN ELLIPSIS, PARABOLA, CONE, &c.-See Glossary I., Cone and Conic Sections. MAJOR AND AXIS MINOR OF AN ELLIPSIS, are the same as the Transverse and Conjugate Diameters, which see in Glossary I. AZIMUTH.-See Glossary II., Astronomy, pp. 36 and 256, and Navigation, page 27. COMPASS. See Glossary II., and Navigation, page 30. MAGNETIC.-See Glossary II., article Horizon. BEARING, in Navigation, is the situation of one place from another with respect to the points of the compass. Thus if A lies in the direction of south-west from B, then to an observer at B, A is said to bear south-west, or to have a south-west Bearing; while to an observer at A, the point B will bear north-east, or have a northeast Bearing.-See Navigation, page 15. BERGS. The Swedish Berg is a hill or mountain; and hence the name of Bergs, or more generally Icebergs, is given to the mountains of ice which are met with in the Polar Seas. Flat sheets of wide-spread ice are termed Fields; and small portions (because found floating) are Floes. BISSEXTILE.-See Calendar. CALENDAR OR KALENDAR. This term is understood to have been derived from the Greek kaleo, I call or proclaim, because the first appearance of the new moon was watched for and proclaimed; and hence the first days of the several months were marked Calendæ (the Calends) in the Calendar, or Almanac of the Romans. Time, as measured by the revolutions of the sun and moon, is divided into days, months, and years. The Months (Mooneths) were at first meant to denote the period of a lunar revolution, or the time from one new moon to another; and the years were counted by the revolutions of the sun-from the shortest day (daylight) to the shortest day again, or from the point of time of the vernal equinox to its return. The solar year, however, does not contain an even number of lunations; and calendars were made to shew the connexion between them. The earliest known Roman year consisted of 304 days, divided into ten months, or moons; and hence the names September, October, November, and December, from the Latin words for 7, 8, 9, and 10. Two more moons were prefixed by Numa, making up 354 days, or about 12 lunations. This period, however, being still less than a revolution of the sun, Julius Cæsar reformed the calendar, by lengthening the several months (to the same extent as they now are), so as the year should consist of 365 days; and as the sun is nearly six hours longer in performing his apparent annual circuit, every fourth year was made 366 days, by adding a day to the month of February. This addition of a day to every fourth year is known at present by the name of Leapyear; but the Romans did not add it to the end of February, as we do, but intercalated it after the twenty-third, so that the twenty-fourth day was counted twice: this day, usually termed Sextilis, was therefore Bis-sextilis; and consequently the Bissextile is another name for Leap-year. The subsequent reformation of the calendar by Pope Gregory XIII., now called the Gregorian Calendar, and the reasons for that reformation, are amply, though concisely explained, in the History of Astronomy, at pp. 37, 47, and 48, to which we refer. CALENDAR MONTHS contain the number of days marked to each in the calendar, as distinguished from Lunar Months, which are legally of four weeks or twentyeight days: of course, neither of these periods corresponds to a lunation. CANICULAR PERIOD. The Dog-star is otherwise called Sirius and Canicula (Latin, Canis, a dog); and what is connected with that star is termed Canicular. The Dog-days (or Canicular days) in the ancient calendars were forty days; reckoning twenty before and twenty after, the heliacal rising of Sirius. That period, being then the hottest of the year, was, by the Greeks, accounted the season of "fevers, plagues, and death." The time of the heliacal rising of the dog-star, however, (what the astrologers of old never |