ADVERTISEMENT 



TO 



THE SIXTH EDITION, PRINTED IN MARCH 1840. 



I have already explained, in the advertisement to Part I., why I felt it right to make no change in the 

 narrative part of this work. But I have found it indispensable to make some alterations in the Appendix. 



The original edition of this appendix contains a Memoir on the Navigation of the South* American Station, 

 a table of the latitudes and longitudes, and several other papers of a professional and scientific nature. All 

 of these, with the exception of the table of latitudes and longitudes, I have resolved to leave untouched. 



It was my habit when navigating on any coast of which the geographical positions were inaccurately 

 determined, not to waste my time in trying to ascertain the actual longitude of each point visited, but rather 

 to measure the differences of longitude between place and place, and especially between some one principal 

 port, on the station selected, from the rest, as being the most frequently visited. Thus, on the coasts of Chili 

 and Peru, I made Valparaiso the first meridian to which all the others were referred. Of course, if the differ- 

 ences were correctly measured, the longitude of all these places would partake of any error which belonged 

 to the assumed longitude of the primary meridian. But it will also be obvious, even to unprofessional 

 readers, that, if at any future time, the longitude of that chief meridian should be ascertained by more 

 numerous and exact observations, the longitude of the other places of which the differences of longitude had 

 been correctly measured, would at once become equally well known with that of the selected port. On this 

 principle, I took Valparaiso as my chief point, and occupied myself in measuring, by chronometers, the 

 differences of longitude between it and all the points on the coast east and west of it, which I visited while 

 sailing backwards and forwards in those seas. 



Subsequent voyagers, both French and English, many of whose opportunities of leisure and other 

 means vastly exceeded mine, having decisively proved that another longitude from that which I assumed 

 must be taken for Valparaiso, I have exchanged for the new one, that originally given in the table, and then 

 by applying my own observed differences to the newly assumed longitude, I have imparted to all other 

 longitudes nearly as great a degree of correctness as that which belongs to the principal point, Valparaiso. 

 The longitude I have now assumed is 71° 40' 18" instead of 71° 31' 00", being a difference of 9' 18", 

 which is the quantity therefore added to all the longitudes in Mr. Foster's table. I have been induced to 

 make this change for the reasons stated by Lieut. Raper, R.N., in his admirable article " on longitudes " 

 published in the Nautical Magazine for 1839, page 758. 



These corrections are easily made ; but it is by no means so easy to correct what may be defective in the 

 sailing directions which form' another part of the appendix, in which the different passages made between 

 place and place on the coasts of Chili, Peru, and Mexico, are described. It is true, that in the works of 

 King, Beechey, Fitz Roy, and others, there is a vast fund of fresh and valuable information on these points ; 

 but I have not found it possible, within any reasonable compass, to apply their observations to the improve- 

 ment of the statements in the appendix, without so materially destroying the original texture, as to deprive 

 it of nearly all the value (whatever that be) which belongs to the integrity of the actual narrative written at 

 the moment, and on the spot, 



I might not, perhaps, have been so scrupulous in this matter, had all these nautical observations been 

 strictly my own ; but as I was very materially assisted, not only in making them, but in recording, and 

 eventually in drawing them up, for the Admiralty, by my late much lamented friend Captain Henry Foster, 

 I feci the strongest reluctance to alter anything which has had the advantage of his masterly handling. 



The loss which the scientific branch of the Naval service has sustained by the untimely-death of this 

 rising young officer, is only to be estimated by those, who, like myself, had the advantage of enjoying his 

 companionship and assistance. Justice to his memory requires me to add, that if I had not been so effici- 

 ently aided in the hydrographic, and in various other scientific departments of this voyage, they must have 

 been almost entirely neglected in the absorbing excitement of the whole scene, or in the paramount obliga- 

 tions of official duties of a totally different description. 



