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PHIPPS’S JOURNAL. 567
fome improvements. The advantagesI imagined might be derived from this inftru-
ment were, a more correét and expeditious manner of determining the pofition of coafts,
and the diftance of fhoals or the fhip from headlands. This inftrument being divided
to ten feconds, an angle may be taken by it with great accuracy to five feconds, The
height ofa fhip’s maft-head above the water being known, it is eafy to find with
this inftrument, by a fingle obfervation, the diftance between two fhips, and confequently
to determine a bafe. ‘The angles being taken with an Hadley’s quadrant from each of
the fhips, to the objects whofe fituations are defigned to be afcertained, the diftance may
be found, and confequently their relative fituations. If there is a megameter in each
fhip, the altitudes taken from both fhips at one inflant, and the angles of the different
parts of the coaft intended to be furveyed obferved with an Hadley’s quadrant at the
fame time, will give the fituation with more accuracy and expedition than any method
of furveying from fhips hitherto practifed ; with the farther advantage of the certain
means of detecting any error in the obfervation, fo as to judge whether it is of fufficient
importance to be attended to. ‘The only precautions neceflary are; to make the ob-
fervations at the fame inftant, to prevent their being affected by any alteration in the
relative pofition of the fhips, as a very fmall one there would occafion a confiderable
error in the diftance ; and to be careful in chufing objects fufficiently defined and re-
remarkable, This method of furveying has the further advantage of giving the fcale of
a coaft: feamen, though they judge very accurately of their diftance from places upon
coafts well known to them, are very often miftaken when they fall in with land they
have never feen before ; of which we had at firft fome inftances in this voyage, the
height of the mountains, before we knew the fcale of the coaft, making us always think
ourfelves nearer the land than we really were. Where the coaft is at all high, the me-
gameter affords a very accurate and expeditious method of determining the height of all
the points, when their diftances are found; and thence, the heights being known, of
afcertaining immediately by a fingle obfervation the fituation of the fhip, or the latitude
of any point by the bearings, at the time of a meridian obfervation: the direction and
rate of currents or tides may alfo be found in this manner with great accuracy. I made
feveral obfervations during this voyage with the megameter, fome of which | fhall give
as examples ; they were fufficient to prove to me the great accuracy that may be at-
tained with this inftrument after fome practice. ‘The utility of fuch a method of ob-
taining a furvey on an enemy’s or undefcribed coaft, as well as that of being able to
prove the truth of charts by a fingle obfervation, is obvious.
~ June the fifteenth, the fhip being in latitude 60° 19’, longitude 0° 39’ W., Hangcliff
bore S. 63° oo’ W.; variation, 23° W.
The altitude of the Carcafs’s maft, by the megameter, was 35’ 48”; height of the
matt, 102,75 feet; hence the diftance between the Racehorfe and Carcafs was 9361
feet: angle between the Carcafs and Hangcliff, 85° 48’; between the Racehorfe and
Hangcliff, 87° oo’: from whence the difference of latitude was found 10’ S. ; difference
of longitude 17’ W.: therefore the latitude of Hangcliff is 60° 9’; longitude 0° 56’ W.
July the fecond, to try how far the megameter could be depended upon, I ob-
ferved the altitude of the Carcafs’s maft 2° 23’ 48’; the angle between the main-
yard and main-topfail-yard, o° 44’ 26’; hence the diftance between the main-yard and
main-top-fail came out = » 31,750 feet.
By meafurement it was found - > 34,125 feet.
Difference 2,375 feet.
The
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