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FOR DETERMINING THE Earlsruhe A.VD LONGITUDE AT SEA,
THE who LE 1 LLUSTRATED wi T H ENGRAv INGs,
THE PRACTICAL NAVIGATOR, .
in this Edition.
THE favourable reception which this Work has met with, emboldens me to present before the Public the present Edition; in which, I trust, I have introduced such improvements as will continue to me the favour which I have so long had the happiness to enjoy. In my former Editions I had digested the several Articles into a natural and simple order, and endeavoured to show how every thing might be deduced from the first and most simple principles of the Mathematics; in which, I trust, I had so far succeeded, as to render it easy to the most common capacity. How beneficial a work of this kind must be to Learners cannot be doubted, when we reflect, that by being thus acquainted with the true principles of things, they will retain better what they have learned, and be enabled to make much greater progress in the art, than could otherwise possibly take place. Indeed, upon a careful perusal of the Work, I found the plan I had pursued, so far as regards the parts of Navigation usually taught and practised at sea, could not be amended in the bulk, though some improvements might be made in particular parts. It particularly occurred to me, that I had invariably found young Gentlemen, who attended me for a private examination, previous to their passing a public one, deficient in working an observation in all the variety of fituations which may take place. In this Work I have accordingly elucidated this important article, by giving a Rule for every different situation, in which the observer can possibly find himself in respect of the Sun; illustrating each with a projećtion on the Plane of the Meridian. There is introduced into this Edition, a Table for the near calculating the Time of High Water, with the assistance of the Nautical Almanack. I pass over many others of smaller note in the first part of the Book, such as partial Amendments of the Style, &c. in haste to give an account of the Arrangements and Additions in the latter part of this Worx, which is for the most part New. Previous to the year 1767, when the first Nautical AlMAN ack was published, the practice of finding the Longitude at Sea was universally by account. The mode of ascertaining it by taking the Moon's distance from the Sun, or a fixed Star, commonly called the LUNAR On servations, was attended with difficulties insurmountable to most Mariners. By the unremitting affiduity of the Astronomer Royal, to whose labours the Nautical Art is much indebted for its present high state of improvement ; and by the Rewards held out by Parliament, 2nd the consequent improvements in-instruments for measuring the Angular Distance, what before was considered as nearly an impossibility, is now come into almost general practice. Proud of contributing my quota towards the facilitating this laudable purpose, so highly conducive to the commercial interests of this powerful Empire, I have endeavoured