"1 Jind published lectures insipid. " ALEXANDER VON HUMBOLDT ta LOUIS AGASSIZ, January 15, 1840 Many things speak against the publication of lectures. The effect of the spoken word is very different from that of the written word. Repeated recapitulations, which help the listener under­ stand, are unnecessary, and the overtones of speech disappear in print. A lecture, particularly when not meant for beginners and not offered in preparation for a test, permits the privilege of subjective choice, and when published it is rightly open to criticism. So it has not been easy for me to determine to publish these lectures, which I have given in various forms in Gattingen and then again in Tiibingen. In the end, the deciding factors were the urging of my students, the encouragement of colleagues, many of whom I was delighted to see among my listeners, and the wish of my publisher, with whom I have enjoyed a friendly relationship for a long time. The final form of the text is basically a copy, and thus reallectures are the heart of it. If the lectures had not been taken down repeatedly, this book would not have appeared; 1 could not have undertaken a textbook-sized compilation of this material. With all the changes, the organization, the line of thought, and of ten the composition of the lectures themselves were retained. They may recall to my listeners of old the hours we spent together.