a i 8 Al'l'ENDIX. APPENDIX. 319
N .l!:
No. 55.
REMARKS on the Chronometrlcal Obsen'ations made during the Surveymg
Voyages of H. M. Ships Adventure and Beagle, between
the years 1826 and 1836.
Before I proceed to notice the chronometrical observations made
during the Beagle's latter voyages, from 1831 to 1836, it appears to
me necessary to give a copy of Captain King's Report of those made
under his direction between 1826 and 1830.
Copy of a Report of the Chronometrical Observations made during a
Voyage for the purpose of sun'ej'ing the southern extremity of
America, in H.M. Ships Adventure and Beagle, between the years
1826 and 1830, under the orders of Captain P. P. King, by direction
of the Right Honourable the Lords Commissioners of the
Admiralty.
Among the important objects to which my attention was directed
by the Lord Commissioners of the Admiralty, upon my appointment
to the command of the Expedition for the survey of the southern part
of South America, was that of measuring the differences of certain
meridians in the north and south Atlantic Oceans by means of
chronometers; and for this purpose I was supplied from the Royal
ObseiTatory at Greenwich with nine chronometers; eight of which,
at the suggestion of the Astronomei Royal, were suspended in gimbals,
and divided into two boxes ; and the ninth, an eight-day boxwatch,
was fitted in the usual manner. The whole were fixed in a
chest that was firmly secured to the deck as low down as possible,
and as near to the middle part of the ship as could be managed, in
order to diminish the effect of the ship's motion, and to counteract
that of the ship's local attraction, which, whatever it might have
been, always remained the same, as the chronometers w^ere never
moved from their positions.
These nine chronometers were made by Mr. French. Their
description and number were as follows :—
Eight-day box chronometer. No. 3233 designated Z
Two-day 3296 A
Two-day 3295 B
Two-day 3271 C
one box.
Two-day 3227 D
One-day box clironometer. No. 3290 designated E l
One-day 3291 FI in
One-day 3292 G ( one box.
One-day 3293 H,
Z had been going at the ObseiTatory for many months, and had
preserved a very regular rate, but all the others were quite new, and
had scarcely settled to a steady rate when I received them.
In addition to the above I was furnished with a pocket chronometer,
No. 553, by Mr. Murray. This watch had been at the Observatory
for several months, and had performed remarkably well: and
before I sailed Messrs. Parkinson andFrodsham intrusted to my care
for trial a pocket chronometer. No. 1048, that was only completed in
time to be sent to me two days before the Expedition sailed from Plymouth.
Mr. French also lent me a pocket-M^atch to use for observing
with, in order that the rest might not be unnecessarily moved.
In the Beagle were three excellent box chronometers. Two by,
Messrs. Parkinson and Frodsliam, Nos. 254 and 228, which, had
been used in the Polar Voyages ; and the third. No. 134,made by Mr.
M'Cabe.
The means, therefore, that were placed at my command to effect
this most interesting object were tolerably ample: and the result
will prove how admirably these machines are adapted to measure
such differences when a great number are employed; because the
irregularities and en-ors of individual watches are compensated for
by employing the mean of the whole.
In the observations for the determination of time, a sextant by
Troughton, No. 1140, and an artificial horizon, were the instruments
used: and the mode, whenever it could be adopted, was that of corresponding
altitudes. Occasionally, however, absolute altitudes were
used, but only in those places where the latitude was correctly
ascertained;—and in some instances the chronometers were rated
by a transit instrument.
The chronometers were always compared with the 'journeyman'
watch before and after the observations, and when corresponding altitudes
were observed all the watches were compared at noon. Their
rates were carefully obsen'ed before sailing from one port, as well as
after the arrival at another; and in calculating the acceleration or retardation
of their rate of going, the correction was obtained by interpolation,
upon the supiMsition of their having changed gradually.
"Whenever it appeared, by comparing the watches with each other,