328 APPENDIX. 



reasons for preferring to give undivided attention to an unbroken 

 series of chronometrical observations, rather than allot any portion of 

 time to independent astronomical observations ; which, to be really- 

 valuable, required what I could not command, namely — time ; a well- 

 placed and good transit instrument ; sldll in its use ; and habits of 

 obsen'ing, which are neither readily nor easily acquired. Besides 

 which, there is always a degree of uncertainty involving the deduc- 

 tions from observations of any celestial phenomena, at a great dis- 

 tance from well-known obsen'atories ; even when the observer and 

 his means are unexceptionable. The causes of this uncertainty are 

 familiar to many, but, as these pages may meet the eye of a reader 

 who is not aware of them, I will mention that the figure of the earth 

 is not yet quite accurately known, that parallax and refraction cannot 

 be allowed for with absolute certainty, that levels and plumb-lines 

 are not everj'where exactly at right angles to, or coincident with, a 

 line di'awn from them to the earth's centre ; and that tables, how- 

 ever excellent, are not perfect. 



That able and indefatigable astronomer, Mr. Fallows, was along 

 time at the Cape of Good Hope before he could determine its longi- 

 tude ; and, after all his exertions, his successors have adopted a 

 result differing from it half a mile.* There is reason to doubt 

 whether Paramatta Observatory is well determined in longitude. To 

 fix that of St. Helena, and that of the Mauritius, occupied much 

 time and talent, aided by excellent instruments in well-built observa- 

 tories. A great deal of time and pains, and ability, have been 

 employed at Madras ; yet, as far as chronometers can tell, there 

 is a great discordance between the hitherto published longitudes of 

 Madras, the Mauritius, and Paramatta, when \iewed in connection 

 Avith their respective meridian distances ; such, at least, as have yet 

 been measured. 



Even on the coast of the Baltic, what differences were found by 

 Lieutenant- General Schubert, in 1833, between the received posi- 

 tions of various observatories, and those which he deduced from the 

 results of fifty-six chronometers ; — placed at his disposal, with a 

 steam-boat, by the Emperor of Russia.f 



But, to return from this digression : — In the Beagle's measure- 



• Mr. Fallows considered the longitude of the Cape observatory to be 

 Ih. 13m. 53s. E. Mr. Henderson Ih. 13m. 55s. E. 



t Journal of the Royal Geographical Society. Vol. VI. Part II. ] 836, 

 pp. 413-6. 



