CONTENTS.

Page.

109

To find the distance of the land in
order to calculate the dip

To find the sun's declination

Variation of the compass

To observe an amplitude or azi-
muth by the compass

To calculate the true amplitude

To calculate the true azimuth

Questions to exercise the learner

in calculating an azimuth

Having the true and magnetic am-

plitude or azimuth, to find the

variation

To calculate the variation by azi-

muths observed at equal alti-

tudes before and after passing

the meridian

Variation observed

On the dip of the magnetic needle

To find the latitude by a meridian
altitude of the sun or fixed star

To find the time of the moon's

passing the meridian.

To find the moon's declination

To find the latitude by the moon's

meridian altitude

To find the latitude by the meri-

dian altitude of a planet

To find the latitude by double al-

titudes

of the sun

of a star

of a planet

of the moon

of two different objects,

taken within a few minutes of

each other, by one observer

of two different objects,

taken at different times

110 Third method of finding the appa-

rent time at sea

111

112

To find the apparent time by an

112 To regulate a watch by equal alti-

altitude of a fixed star

tudes of the sun

113

114

To find the longitude at sea by lu-

nar observations

Page.

156

158

158

160

162

163

164

166

168

174

175

Method of finding the stars used

in lunar observations

114 General observations on the tak-

ing a lunar observation

117

To work a lunar observation

Examples of lunar observations

115 Second method of working a lu-

119 Witchell's improved method of

nar observation

120 Method of taking a lunar observa-

finding the true distance

tion when you have only one

123

124 To calculate the sun's altitude at

observer

any time

176

178

125 To calculate the altitude of any

star

178

180

128 To find the longitude by the eclip-

128 ses of Jupiter's satellites

181

129 To find the longitude by an eclipse

129 of the moon

181

130 To find the longitude by a time-

keeper or chronometer

182

130

To regulate a chronometer by lu-

nar observations

185

First method

Second method

131

133 Problems useful in navigation

138 To find the difference between the

To find the longitude by a varia-

tion chart

185

186

142

150

152

153

Third method

Questions to exercise the learner
in working double altitudes
To find the latitude by one alti-
tude of the sun, having your
watch previously regulated
To find the latitude by the mean

of several altitudes of the sun
taken near noon by a sextant or
circle
To find the latitude on shore by
means of an artificial horizon

To find the latitude by the polar

star

148 To determine the height of a

true and apparent directions of

the wind

191

mountain by barometers

192

Mensuration

193

148 Gauging

Surveying

197

199

To find the content of a field by

the table of diff. lat. and depart-

ure

To find the time at sea and regu-
late a watch

Examples to exercise the learner

in finding the apparent time

To survey a harbour by observa-

tions on shore

Methods of surveying a

205

154

bank or shoal where great accu-

small

racy is required

206

156)

--

SIGNS AND ABBREVIATIONS USED IN THIS WORK.

Is the sign of addition, and denotes that whatever number or quantity follows the sign, must be added to those that go before it, thus 9+8 signifies that 8 is to be added to 9. Or A+B implies that the quantities represented by A and B are to be added. The sign + is called the positive sign.

The sign of subtraction; and denotes that the number following it must be subtracted from those going before it, thus 7-5, signifies that 5 must be subtracted from 7. The sign-is called the negative sign.

X Is the sign of multiplication, and shows that the numbers placed before and after it are to be multiplied, thus, 7 × 9 signifies 7 multiplied by 9, which makes 63; and 7× 8 × 2 signifies the continued product of 7 by 8 and by 2, which makes 112. Multiplication is also denoted by placing a point between the quantities to be multiplied; thus A.B signifies that A is to be multiplied by B.

Is the sign of division, and signifies that the number that stands before it is to be divided by the number following it, as 72+12 shows that 72 is to be divided by 12. Division may also be denoted by placing two points between the numbers, thus, 72: 12 represents 72 divided by 12

72

or by placing the numbers thus, which signifies 72 divided by 12.

() or

12

Either of these marks is used for connecting numbers to

gether, thus, 3+4×6, or (3+4) × 6, signifies that the sum of 3 and 4 is to be multiplied by 6.

Is the sign of equality, and shows that the numbers or quantities placed before it are equal to those following it: thus 8×12=96. Or & mul

tiplied by 12 are equal to 96, and 7+2×4=36.

:::: Is the sign of proportion, and is marked thus, 7: 14 :: 10: 20, that is, as 7 is to 14, so is 10 to 20. Or A: B:: C: D, that is, as A is to B, so is C to D.

Signifies degrees; thus, 450 represents 45 degrees.

'Signifies minutes; thus, 24' or 24 minutes,

Signifies seconds; thus, 44", or 44 seconds.

Signifies thirds or sixtieth parts of seconds; thus, 44", or 44 thirds. S. Signifies sine. N. S. Signifies Natural sine.

Sec. Signifies Secant.

Tan. Signifies Tangent.

Co-sine, Co-tangent, or Co-secant of an arch signifies the sine, tangent or secant of the complement of that arch respectively.

<Signifies Angle; with an s at top Angles, <*

Ʌd Angled,

A Signifies Triangle. A's Triangles.

400

Signifies a square.

or the Sun. O or D the Moon. *a Star. L. L. Lower Limb. U. L. Upper Limb. N. L. Nearest Limb. S. D. Semi-diameter. P. L. Proportional Logarithm. N. A. Nautical Almanac. Z. D. Zenith Distance. D. R. Dead Reckoning.