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590 PHIPPs’s JOURNALs
<¢ When the tube is made on fhore, the beft fubftance for the purpofe is thin cops
per well tinned, this being more durable in long voyages than tin plates.
“ Inftead of mopping, the tube, if required, may have a cafe made alfo of copper,
fo much larger in diameter as to admit a thin fheet of water to circulate between
them, by means of a fpiral copper thread, with a pipe of an inch diameter at each end
of the cafe; the lower for receiving cold water, and the upper for carrying it off when
heated.
<¢ When only a very fmall portion of room can be conveniently allowed for diftilla-
tion, the machine, which is only twenty-feven inches long, may be fubftituted ; as was
done in this voyage. ‘The principal intention of this machine, however, is to diftil
yum and other liquors; for which purpofe it has been employed with extraordinary
fuccels, in preventing an empyreuma, or frery tafte.”
\
Account of the Aftronomical Obfervations and Time-keepers, by Mr. Lyons.
< Tur obfervations for finding the time at fea, were taken with a brafs Hadley’s
fextant of eighteen inches radius, made by Dollond; and fometimes by Captain
Phipps, with a fimaller of four inches radius, made by Ramfden, which commonly
agreed with the other within a minute. The error of the fextant was generally found
by obferving the diameter of the fun; which if the fame as double the femidiameter
fet down in the Nautical Almanac, fhewed that the inftrument was perfectly adjufted ;
if it differed, the difference was the error of the fextant. It was neceflary to know this
error of adjuftment very exactly, and therefore I generally repeated the obfervation of
the fun’s diameter feveral times, and from the mean of the refult found the error of the
fextant. ‘This error will equally affect all the obfervations taken near the fame time,
and therefore eannot be difcovered from the comparifon of feveral obfervations.
Under the equator, an error of one minute in altitude, near the prime vertical, will
only produce an error of four feconds in the apparent time; but in the latitude of
eighty degrees it will caufe an error of twenty-three feconds. As we generally took
feveral fucceflive obfervations, any error in the obfervation itfelf will be generally in-
dependent of the reft; and as I have calculated each feparately, the conclufions will
fhew which are erroneous, by their differing much from the ‘mean of all, which can-
not but be very near the truth.
«¢ In calculating thefe obfervations, I found by the logboard how much we had
altered our latitude fince the laft obfervation; and fometimes, when we had an obferva-
tion the noon following the obfervation for the time, the latitude of the fhip at the
time the altitudes were taken was inferred from it. As moft of our altitudes were ob-
ferved when the fun was near the prime vertical, a {mall error in the latitude will not
produce any confiderable change in the time; indeed, if it is exa¢tly in the prime
vertical, it will not make any change at all.
“« Yo find the longitude from thefe obfervations: to the apparent time found by
calculation, apply the equation of time according to its fign, which will give the mean
time; the difference between which and that marked by the watch, will fhew how
it is too flow or too faft for mean time.
<¢ Captain Phipp’s pocket watch, made by Mr. Arnold, when compared with the
regulator at Greenwich, May 26th, was twenty-four feconds too flow; it was there
found to lofe twelve feconds and a quarter a day on mean time. From this it is ealy
to find what time it is at Greenwich at any moment fhewn by the watch.
¢.The
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