AUTHOR'S PREFACE. IN COMPLIANCE with many requests, I beg to offer to the public a series of popular Lectures which I have delivered on various occasions. They are designed for readers who, without being professionally occupied with the study of Natural Science, are yet interested in the scientific results of such studies. The difficulty, felt so strongly in printed scientific lectures, namely, that the reader cannot see the experiments, has in the present case been materially lessened by the numerous illustrations which the publishers have liberally furnished. The first and second Lectures have already appeared in print; the first in a university programme which, however, was not published. The second appeared in the Kieler Monatsschrift' for May, 1853, but owing to the restricted circulation of that journal, became but little known; both have, accordingly, been reprinted. The third and fourth Lectures have not previously appeared. These Lectures, called forth as they have been by incidental occasions, have not, of course, been composed in accordance with a rigidly uniform plan. Each of them has been kept perfectly independent of the others. |