[Sidenote: Reef Island.]

Reef Island lies west by north, about two leagues from Napakiang Roads; on the north side the reefs stretch a great way, but the south is more clear.

Between Napakiang and the Sugar Loaf there is no place for ships to lie in safety; the bay immediately to the north was examined by Mr. Mayne, master of his Majesty's ship Alceste, when two shallow harbours were found.

[Sidenote: Tides.]

The flood runs to the northward and eastward, along sh.o.r.e, and the ebb in an opposite direction. The rise and fall is about nine feet perpendicular. High water at full and change IX.

[Sidenote: Variation of the compa.s.s.]

The variation of the compa.s.s, determined with great precision by the transit azimuth instrument, was 52' westerly.

The longitude of the Lyra's observatory at Napakiang by the mean of thirty-six lunar observations on both sides of the moon, is 127 37' 28"

east; by four chronometers, agreeing nearly, 127 38' 30" east. The lat.i.tude is 26 13' 39" north.

[Transcriber's Note: Crescent moons are denoted by [((] or [))]; a circle with a period therein is denoted by [(.)]]

OBSERVATIONS MADE AT NAPAKIANG OBSERVATORY, GREAT LOO-CHOO ISLAND.

Lunars with a s.e.xtant. Lunars with a s.e.xtant.

[(.)] West of [((] *[Greek: a] Arietis, East of [))]

25th September, 1816. 4th October, 1816

[(.)] [((] 127. 38'. 15" East. * [))] 127. 31'. 00" East.

35 . 15 37 . 00 36 . 15 43 . 00 34 . 45 52 . 30 33 . 00 54 . 30 36 . 00 38 . 45 30 . 45 52 . 45 28 . 30 50 . 15 32 . 15 50 . 30 31 . 30 127. 33'. 39" Mean 41 . 45 40 . 30 26th October, 1816. 34 . 15 43 . 15 [(.)] [((] 127 . 38 . 30 39 . 45 39 . 45 ------------ 41 . 30 Mean by s.e.xtant 127 . 43. 20 * East of [))]

44 . 15 44 . 30 Lunars by Circle.

32 . 15 [(.)] West of [((]

33 . 00 31 . 45 4th October, 1816 31 . 15 [(.)] [((] 127. 38'. 45"

27 . 30 127 36'. 16" Mean 32 . 30 ------------- ------------- Mean by s.e.xtant 127 . 34 . 58 [(.)] W. [((] Mean 127 . 35 . 37 by circle.

Mean by s.e.xtant [(.)] west [))] 127 34'. 58"

* East [((] 127 . 43 . 20 -------------- Mean longitude by s.e.xtant [(.)] * [))] 127 . 39 . 9 by circle [(.)] * [((] 127 . 35 . 37 -------------- Mean longitude by 36 lunars 127 . 37 . 28 Longitude by chronometers 127 . 38 . 30 east of Greenwich.

LAt.i.tUDE OF NAPAKIANG.

_By Meridian Alt.i.tudes of the Sun and Alt.i.tudes taken near Noon._

By meridian alt.i.tudes observed. By meridian alt.i.tudes deduced in the usual way from sights taken near noon.

1816. 1816.

s.e.xtant. 8th Oct. mean of 3 A.M.} 26. 13'. 30" circle.

17th Oct. 26. 13'. 43" and 3 P.M. }

20th Oct. 26 . 13 . 44 20th Oct. A.M.{ 26 . 13 . 46} s.e.xt.

{ 26 . 13 . 44}

Circle.

26th Oct. 26 . 13 . 29 20th Oct. P.M.{ 26 . 13 . 58} { 26 . 13 . 47} s.e.xt.

{ 26 . 13 . 57}

22d mean 2 A.M.& 2 P.M. 26 . 13 . 24} circle.

26th 3 P.M. 26 . 13 . 29}

Lat.i.tude by mean of 3 meridian alt.i.tudes 26. 13'. 39" s.e.xtant and circle.

mean of 5 alt.i.tudes near noon 26 . 13 . 50 s.e.xtant.

mean of 3 do. do. 26 . 13 . 28 circle.

------------ Mean lat.i.tude 26 . 13 . 39 north.

VARIATION OF THE COMPa.s.s AT NAPAKIANG.

The declination of the magnetic meridian was ascertained with considerable precision by means of the transit azimuth instrument: the needle seldom showed the same variation, as it oscillated about ten minutes, but the mean position of the magnetic meridian was 52' 10" west of the true. A coral reef was selected for the place of these observations, in order to avoid the attraction arising from buildings, or from inequalities in the ground.

_Variation observed on board by Walker's Azimuth Compa.s.s._

29th Sept. 1816, P.M. ship's head W. by S. variation by

1st azimuth 0. 51'. 30" west.

2nd 0 . 53 . 30 3rd 1 . 17 . 30 Amplitude 1 . 15 . 00 30th A.M. 1st azimuth 0 . 55 . 30 2nd 0 . 34 . 15 3d Oct. A.M. ship's head E.N.E. 1st azimuth 0 . 37 . 00 2nd 0 . 48 . 00 ----------- Variation by mean of 7 azimuths and 1 amplitude 0 . 52 . 39 west.

TABLE OF OBSERVATIONS

MADE WITH

DR. WOLLASTON'S DIP SECTOR:

WITH AN ENGRAVING, AND A DESCRIPTION OF THE INSTRUMENT, AND DIRECTIONS FOR ITS USE.

[Ill.u.s.tration: Wollaston's Dip Sector]

EXPLANATION OF THE DIP SECTOR,

AND