The second edition of the _Views of Nature_, was published by me in Paris in 1826. Two papers were then added, one, “An inquiry into the structure and mode of action of Volcanos in different regions of the earth;” the other, “Vital Force, or The Rhodian Genius.” Schiller, in remembrance of his youthful medical studies, loved to converse with me, during my long stay at Jena, on physiological subjects. The inquiries in which I was then engaged, in preparing my work “On the condition of the fibres of muscles and nerves, when irritated by contact with substances chemically opposed,” often imparted a more serious direction to our conversation. It was at this period that I wrote the little allegory on Vital Force, called The Rhodian Genius. The predilection which Schiller entertained for this piece, and which he admitted into his periodical, _Die Horen_, gave me courage to introduce it here. My brother, in a letter which has recently been published (William von Humboldt’s Letters to a Female Friend, vol. ii. p. 39), delicately alludes to the subject, but at the same time very justly adds; “The development of a physiological idea is exclusively the object of the essay. Such semi-poetical clothings of grave truths were more in vogue at the time this was written than they are at present.” In my eightieth year I have still the gratification of completing a third edition of my work, and entirely remoulding it to meet the demands of the age. Almost all the scientific illustrations are either enlarged or replaced by new and more comprehensive ones. I have indulged a hope of stimulating the study of nature, by compressing into the smallest possible compass, the numerous results of careful investigation on a variety of interesting subjects, with a view of shewing the importance of accurate numerical data, and the necessity of comparing them with each other, as well as to check the dogmatic smattering and fashionable scepticism which have too long prevailed in the so-called higher circles of society.