Connected by the most intimate bonds of friendship over the five years of our travels (and since then), Bonpland and I have jointly published the whole of our work. I have tried to explain what we both observed but, as this work has been written from my notes on the spot, all errors that might arise are solely mine. In this introduction I would also like to thank Gay-Lussac and Arago, my colleagues at the Institute, who have added their names to important work done, and who possess that high-mindedness which all who share a passion for science should have. Living in intimate friendship I have consulted them daily on matters of chemistry, natural history and mathematics.