APPENDIX. 



345 



Having given the principal results — those forming links of the 

 chain of meiidian 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 observations. 



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 Callao 

 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 minor 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 Terns. — 

 f f 



■1836^ 



