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fore, as a grateful Acknowledgment of the many Favours received, I humbly beg leave to Dedicate this Piece to you; and am with the greatest Regard

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; H E R E are so many Books of Navi§§g gation already extant, that it may seem .3 impertinent to trouble the World with a so new One; especially since some good Ma#ho thematicians both at home and abroad, -- * and many who were perfeit Masters of the Prattice, have written on this Subjeśī. The former of these being fond of ingenious Speculations, have generally been too prolix on the Theory, and too short on the praffical Part. Whereas the later have in a great MeaJure negletted the Theory, and not being very solicitous about Language or Method, have delivered the praślical Rules in such a Manner, as they cannot be easily comprehended, and much less remembred, especially since there is seldom mention made of the Reasons on which they deend. p But I am very far from finding fault with all the Books on this Subječi; for there are some very full both on Theory and Pračice, against which, I have no other Obještion but that they are too tedions to be taught, and too dear to be purchased by moff People.

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2%uth ought to learn the Elements from shorter Trea-
tises, and afterwards at their leisure should read gene-
ral Systems, in order to perfeit them.
For these Reasons, I have ventured to publish this
small Treatise; wherein I have made it my chief Bus-
mes; to keep a due Medium betwixt the two Extremes,
into which the speculative Writers on the one Hand, and
the praślical ones on the other are apt to run. I have
laid down all the useful Rules, and troubled the Reader
with no more of the Theory than is necessary to explain
them. I have also explained the principles of Mensura-
tion, Surveying, aud Gauging, and shewed how they are
applied to Pračice, in order that my Book might better
answer the particular end for which it is designed, namely,
the Instručiion of the young Gentlemen of Mr WATT so
Academy.
As for the particular Contents of each Sečion, the Rea-
der will find them at the end of the Book, and therefore
they need not be repeated here. I shall only observe, that
I have designedly omitted Great Circle Sailing, as be-
ing only speculative, and depending on Spherical Trigo-
nometry, which would require a particular Volume to
explain it. There are indeed two or three Problems ne-
cessary in Praffice, which depend on the Resolution of
Spherical Triangles; but for the Solution of these, I have
laid down such clear and short Rules that no body can
mistake the manner of applying them. A -
... I know, some are of Opinion, that the Demonstra-
tions are not to be easily learnt by every Capacity, on
which account they teach the Pračice only. This Book is
therefore so written as to serve for their purpose likewise,
because they may take the Rules alone without their Reas
sons. It is true indeed, that there may be great Diffical-
ty in finding out a proper Demonstration; but after it is
found, it is easier to be understood than that of which it
is the Reason; and therefore they who are not capable of
wnderstanding the Demonstrations, are much less capable
of understanding the Pračical Rules which * on
- them.

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