Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

APPENDIX. 345 Having given the principal resnlts — those forming hnks of the chain of meridian distances carried round the globe — I have to men- tion that all others of a similar nature, obtained by the Beagle's officers, are based upon them, and that in no one instance do any of the longitudes given in the accompanying tables depend upon absolute or independent astronomical obser^'ations. It ought to be clearly stated, however, that the sum of all the parts which form the chain amounts to more than twenty-four hours, therefore error must exist somewhere ; but what has principally caused the error, or where it may be said to exist, I am unable to determine. The whole chain exceeds twenty-four hours, by about thirty-three seconds of time. It appears very singular, that the more the various links of this chain are examined and compared with other authorities, the more reason there seems to be for believing them correct, at least to within a very small fraction of time ; and even allowing that each link were one or two seconds of time wrong, it does not appear probable that all the errors would lie in one direction, unless some hitherto unde- tected cause affects chronometers when carried westward, which might affect them differently when carried eastward. It would ill become me to speak of any value which may be at- tached to these chronometrical measures ; even erroneous as they undoubtedly are in some part, if not to a certain degree almost every where. I can only lay the honestly-obtained results before persons who are interested in such matters, and request that they may be compared with those of the best authorities. Callao, Sydney, and the Cape of Good Hope, are three remote points which might be selected rather than others, because generally supposed to be well determined. If the Beagle's position of CaUao be proved incorrect, then must Humboldt's (calculated by Oltmanns), adopted by Daussy,* be also incorrect ; and if her position of Sydney (reckoning eastward from Greenwich) be materially wrong, then must the best authorities for the longitude of that place be also in error, for they differ from the Beagle only about eight or ten seconds, which is but a mmor part of thirty-three seconds. The only idea I can dwell on, with respect to the cause of this error of thirty-three seconds, is, that chronometers may be affected by * Connaissance des Tems. — 1836. f f