330 APPENDIX.
to State, that in no one instance did it differ a quarter of a second
from theirs; indeed the figures would bear me out in saying,
that it did not dilfer even a tenth of a second ! These facts are well
known to Lieut. Stokes, Lieut. SuUvan, and Mr. Usborne.
Tlie sextant used throughout the voyage for this purpose, and this
alone, was a particularly good one, made expressly for me by Worthington
and Allan. Its index error never varied, nor was it ever the
least out of adjustment. Between morning and afternoon observations
it was more than usually guarded, and on no account handled,
or exposed to a change of temperature.
Latitudes were obtained by other sextants, and by circles. I was
always anxious to get many results, not only by one observer, or instrument,
but by several observers, and diiferent instruments. It
sometimes happened that there were six observers seated on the
ground, with as many different instruments and horizons, taking the
sun's circum-meridian altitudes, or observing stars at night. Where
so many were working against one another, errors were soon detected,
either in observation or in computing. I have alreadv mentioned
that Dr. Inman's method of calculation was followed; but it
remains to be shown what mode of interpolation was adopted when,
as was usually the case, most of the watches were found to be going
at rates diiferent fi'om those ascertained at the preceding place of
rating.
With very few exceptions, the method used by Dr. Tiarks* was
practised ; and, in the excepted cases, that used by Hinders, Owen,
Foster, Kmg, and others, was employed. The following are the
principal results upon which all others obtained during the Beagle's
last voyage (1831-6) depend. Want of room alone prevents my giving
the minutest details upon which they depend; it would be of
little use to give computations without comparisons, or comparisons
ivithout rates, or rates without the calculations and observations on
which they depend ; or any part of these without the whole, which
constitutes a mass of figures filling several thick foHo books. All these,
however, will be deposited at the Hydrographical Office, so that any
one who will take the trouble may, after obtaining the Hydrographer's
permission, examine them to the fullest extent.
Our first station was at the Devonport Baths, exactly in the meri-
* Chanticleer's Voyage—Appendix, p. 226-8.
APPENDIX. 331
dian of the centre of Government House. By the published survey of
Plymouth and Devonport,* the Government-House at Devonport
is 0° 48" west of Plymouth old church, the longitude of which is
given by Captain King in the preceding copy of his report.
This longitude, however, differs slightly from that obtained by the
Beagle's chronometers carried from Devonport to Greenwdch ; and
as the longitude of Falmouth, by her chronometers, agrees with that
determined by Dr. Tiarks, I have used in the construction of the
table of positions (pp. 65-85) the result obtained directly by these
chronometers, because so confirmed.
PmNciPAL RESULTS of the Beagle's chronometrical measurements
between 1831 and 1836; forming a connected chain of meridian
distances around the globe, the first that has ever been completed,
or even attempted, by means of chronometers alone.
D E V O N P O R T t o PORT PBAYA.
Twenty Chronometers. Twenty-three Days.
H. M. s. H. M. S. H. M. s. H. M. S.
A 1 J7 21,68 M 1 17 20,47 =0,47
21,8o N 24,42
0 20,69 p 17.73 D '7,03 R E 19,90 19,90 20,33 S 20,52
F 23,03 V 22,23
G 21,43 w 20,93
17,16 X 21,08
K , 23,90 Y 20,58 20,58 L 31,12 z 21.43 21,43
Mean ... 20,87 30,74
Preferred Ih. 17 m. 20,7s.
Places of observation:
The Baths, in the meridian of Government-house, at Devonport.
The landing-place at the west side of Quail Island, Port Praya, in
the Cape Verde Islands.
' lu the above-mentioned plan, published by the Admiralty, on a scale
of 5,03 inches to a mile, the departure between Devonport Baths and
Plymouth Old Church is 5,8 inches ; which in latitude 50° 22' represents
0° 1' 48"1 of longitude.
e e 2