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[[top right corner]] 174 [[/top right corner]]

[[top left corner]] Gents Mag. p.12. 1738. [[/top left corner]]

[[underline]] To find the [[/underline]] Longitude [[underline]] at Sea. [[/underline]]

Let first a Table be made of the Moon's Place at a known Longitude, not by Calculation, but by observing the Moon rise or set, thus:

[[note on left]] Method of finding the Longitude by the Moon. [[/note on left]]

At the first Appearance of her Vertex, if the Sea be smooth, or if rough, I am to be 30 or 40 Foot high, where I can see 8 Miles off, at which Distance the Height of a Wave is inconsiderable; I observe the Hour, Minute, and Second, by a Star. and so, by the Moon's Node, the Difference of their R. Ascension; and suppose it an Hour before 6: Then in the Figure, 

[[note on left]] [[strikethrough]] Plate [[/strikethrough]] Fig. 4A. [[/note on left]]

MN being the Moon's Path, and N the Node, the Angle EPN is 15 degrees, and PE being 90, and PEB the known Latitude, I can find PB, which taken from NP I have BN, also I can find PBE, or EBN, which, with PNM, the Angle the Moon's Path makes with the Meridian the Node is in, will give Nn: Then I want only a C, to know how far the Moon's Center is from the Node, whose Place may be known to 2 or 3 Seconds, tho' the Moon's Place not to half a Degree; if then I subtract the Refraction from the Moon's Parallax, and the Minutes the Horizon is depressed by my being 40 Foot high, from the Remainder (which may be known by [[underline]] Wright's [[/underline]] Table in his Correction of Errors) I shall know how much the Moon's Vertex, and so her Center, is above the Horizon (i.e.) CO, which, with the Angle n, gives Cn to be added to Nn, and I have her Distance from the Node, or her Place at that Hour by the Node or because the Node is too movable, by the first Star of [[underline]] Aries [[/underline]]; and suppose it is 4 degree Hours by

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