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Cidon:
PUBLISHED BY PARBURY, ALLEN AND CO. OLIVER AND BOYD,

EDINBURGH; AND BY J. AND A. WALKER, LIVERPOOL.

1831.

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PREFACE.

In the composition of this work, the principal object has been, to furnish Navigators with short and convenient methods of performing the necessary calculations, in the practice of ascertaining the Longitude by Lunar Observations, or Chronometers.

In finding the Longitude by means of the Moon's Distance from the Sun, or a Star, the most tedious and difficult part of the calculation, is to clear the Apparent Distance from the effects of Parallax and Refraction; the mode of performing this part of the operation, given in the present work, is extreniely simple, and is perhaps the most convenient method of calculation that has ever been offered to the Public: It may be performed in a third part of the time that is required for the common methods.

The computation of the Apparent Time from the Altitude of the Sun, or a Star, is necessary, whether the Longitude be deduced from Lunar Observations, or Chronometers; this calculation is rendered very easy, and may be performed in about haif the time required, when the common Tables are used.

A variety of Examples are given, to illustrate the use of the Tables; with occasional remarks on the nature of the Corrections, the mode of making the necessary observations, and the management of Time-keepers. These rernarks, it is presumed, will be fuund useful to the young navigator, and to others who leave not had much experience in the modes of finding the Longitude by Lunars

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