# The Practice of Navigation and Nautical Astronomy

J. D. Potter, 1882 - Nautical astronomy - 910 pages

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### Contents

 INTRODUCTION 1 NAVIGATION 55 The Sailings 82 Mercators Sailings 95 Taking Departures 114 Charts 122 The Ships Journal 132 NAUTICAL ASTRONOMY 143
 Finding the Time 260 Finding the Variation of the Compass 308 The Tides 317 NAVIGATING THE SHIP 329 Explanation of the Tables 3tt6 365 PHENOMENA 399 Spherical Traverse Table 486 Apparent Dip of the Sea Horizon 625

 REDUCTION 147 Taking Observations 175 ELEMENTS 183 Subordinate Computations 187 Finding the Latitude 225
 Augmentation of the Moons Semidiameter f39 640 VARIATION 650 LOGARITHMS Arc 782 Index to the Maritime Positions 879 General Index 903

### Popular passages

Page 41 - The angle in a semicircle is a right angle ; the angle in a segment greater than a semicircle is less than a right angle; and the angle in a segment less than a semicircle is greater than a right angle.
Page 19 - The characteristic of a number less than 1 is found by subtracting from 9 the number of ciphers between the decimal point and the first significant digit, and writing — 10 after the result.
Page 38 - A parallelogram is a four.sided figure, of which the opposite sides are parallel; and the diameter is the straight line joining two of its opposite angles.
Page vii - This is the more important, as very indistinct and erroneous notions prevail among practical persons on the subject of accuracy of computation ; and much time is, in consequence, often lost in computing to a degree of precision wholly inconsistent with that of the elements themselves. The mere habit of working invariably to a useless precision, while it can never advance the computer's knowledge of the subject, has the unfavourable tendency of deceiving those who are not aware of the true nature...
Page 147 - For the same body the semidiameter varies with the distance; thus, the difference of the sun's semidiameter at different times of the year is due to the change of the earth's distance from the sun; and similarly for the moon and the planets.
Page 22 - A CIRCLE is a figure bounded by a curve line called the circumference,* of which every point is at the same distance from a point within, called the centre. Thus, ABD is a circle, and C the centre.
Page 43 - ... section shall be parallel to the remaining side of the triangle. Let DE be drawn parallel to BC, one of the sides of the triangle ABC: then BD shall be to DA, as CE to EA. Join BE, CD; then the triangle BDE is equal...
Page 37 - ... the three interior angles of' a triangle are together equal to two right angles.
Page 39 - Hence it is plain that triangles on the same or equal bases, and between the same parallels, are equal, seeing (by cor.
Page 105 - The distance between two points on the surface of a sphere is the length of the minor arc of a great circle between them.