1

and minutes, and alfo its length muft be accurately measured to feet and parts, either by a measuring chain, or by a piece of log-line of 100 feet long, properly marked at the end of every 10 feet.

From one end of the base observe, with any inftrument proper to take bearings, the pofition or bearing in degrees and minutes of all the ftaves or objects within view, and write them down orderly; do the fame from the other end of the base, and let all the bearings be corrected by the variation of the compass.

Then these measures and corrected bearings being plotted or laid down, will give the most confpicuous points on fhore, the intermediate spaces are to be filled up from the fketches of them made on the spot.

But if any fuch objects should spread on either hand, fo far from beyond the limits of the bafe, that at either end thereof, the other end and those objects or staves fhould appear nearly in the fame direction, or to make <s of, not exceeding 10°: or, if fome of the remarked objects can be feen only from one end of the base, then let the bearings of such objects be taken from a place whofe pofition has been determined from both ends of the measured base; or if there are several remarked objects which cannot be seen from either end of the base lines, let the bearings of fuch objects be taken from each of the two points whofe pofition has been taken from both ends of the bafe; or, it may on fome occafions be proper to choose another place on which another base of a convenient length may be measured, and from the extremities of which the ends of the first base may be feen, and alfo as many as can be of the remaining objects which lay too obliquely for the first base, or which could not be seen from it; in fuch manner proceed until the bearings are taken of all the points judged neceflary for completing the furvey of the limits of the harbour.

If a bafe line of a fufficient length cannot be measured in one right line, it may be taken in two adjoining lines, as the two fides of a triangle, the included angle being accurately taken, and the bearing of either line.

When the outlines or limits of an harbour, bay, road, &c. are delineated by the preceding precepts, let a fmall veffel go out to fea to take drawings of the appearance of the land, and its bearings, fail likewife into the harbour, and draw the appearance of its entrance; take particular notice if there are any falfe refemblances of the entrance by which fhips may be deceived and run into danger; or when any two objects being brought in a line, or in one, will lead into the harbour without danger; when it can be done, fearch for the best anchoring places, and if poffible denote thofe places, by bringing two objects in one, if not the exact bearings of two or three other objects, fo that the places may be eafily determined, the chart being correctly drawn, a compafs with the váriation, and scale properly fitted to the plan, the ifles, rocks, fands, &c. marked in their proper places, with their foundings at low

ings all the way to those anchoring places, the proper failing marks to avoid dangers; the winds, if any troublesome ones, which prevail, and at what feafons; the places where fresh water can be got, the name of the place, the country in, on what fea, the latitude and longitude, a sketch of the appearance the place makes at sea upon a known rhumb, and at an effimated distance, and whatever else a judicious feaman fhall think proper to infert; then is the plan fit for all nautical purposes, and may be embellished with proper colours, if neceffary.

Sea-drawings, taken according to the foregoing precepts, befides the real ufe they are of, cannot fail to recommend the young mariner who furveys and conftructs them, to the notice of his supe riors.

WITH

To reduce a Draft to a smaller Scale.

TITH a black lead pencil draw the draft to be reduced all over with cross-lines, forming exact fquares, draw the clean paper for the copy all over with the fame number of squares, but their fides larger or fmaller in proportion to the intended fize of the fcale, fuch as,, &c. length of the other, diftinguish by a stronger mark, with a figure every fifth or fixth row of fquares in both, fo that the feveral correfponding fquares may be readily perceived; then, in each of the fquares of the draft, draw, by the eye, a curve on the paper, fimilar to that in the fquare of your copying draft, till the whole is copied; make the black lines with India or other ink, and when drawn, the black-lead lines may be rubbed out with bread or India rubber.

I here give two Examples, as an elucidation of what has laft been faid.

These instruments give the points GC DE HF in order from each station; that is, BG and AG interfect, as alfo BC and AC,

&c.

Obferve, the last letter must be the fame in both bearings, and it will be the beft to follow the bearings one way all round the compafs from the firft ftation; as alfo when arrived at the fecond ftation, begin with your firft object feen at first station, and follow the letters round belonging to each object, by which the laft letter in each bearing will fucceffively follow in order.

This is an example when on board ship.

EXAMPLE II.

This harbour was furveyed by bafe lines taken on fhore, which, when it can be done, is far preferable.

The bafe line AG 812 fathoms, was taken, as by directions, on the most even spot on fhore; now, beginning from the point A : JGB=S. S. W. Bearings GC W. by S. from Sta-GD-W. 3 N. tion A. GE=W.N.W.N. GF=N.W.by N.IN.

AB W. by S. & S.
AC-W. by N.
AD W.N.W.IN.
AE N.N.W.W.
AF N. by W.jw.
AGEN. N. E.

812 fath.

S

Bearings from
Station G.

After having made thefe obfervations, it will be neceffary to proceed to the northern part of the coaft. In all cafes where a coaft is furveyed in feveral parts, it is moft advisable to measure a new fundamental bafe for each part, when it can be conveniently done. A line measured from the ftation F, towards K, is well adapted to our purpose. Let FK, therefore, be the second bafe line; its length, by admeasurement, is found to be 778 fathoms; and its bearing, by compafs, N. E. E. Take bearings from each end of

this base as before.

Bear- (KFS.W.4W. 1

FlandFH N.W.byN.IN. | ings | KH-N.W.IN.
FL=N.E.

FK N.E.4E.778 fath.

Bearings

from KI=W.IS.
Sta- | KLN.byW.
tion F LKN N.E.4W.J

from Sta

tion K.

It is plain, that the connection between the two parts of this furvey is preferved by the fecond fundamental bafe being drawn from the point F, whofe fituation was before determined by obfervations from the firft bafe line. If this particular pofition of the first bafe line had not been convenient, and it had been taken at a diftance from every point determined in fituation from the firft bafe line, the connection would have required an observation of the bearing of one of the faid points from each end of the fecond bafe. Thus, fuppofe the line IK to be the fecond base line, instead of FK, the pofition of IK, with refpect to the given point F, may be known by taking the bearing of F from I and K. The end of the fhoal, marked M, lies with Ď, bearing N. and E. N. by E. E.

All the obfervations which are required to be made on fhore being completed, through the interfections of the bearings draw the configuration of the coaft, as before directed, and finish the drawing by the inftructions there given; which, if well attended to, no difficulty can well occur.

To find the Height and Distances of Objects at Sea. HEN the object is perpendicular, and the distance to it can be measured, find the angle of altitude with a quadrant, and meafure the diftance to it as exact as poffible, and then you have

W