一般注記"The book is an outgrowth of my research ... activities in Bell telephone laboratories. Its first draft was prepared in connection with courses of lectures in the laboratories' 'Out-of-hour' program. Courses were given in 1933-34 and 1934-35, for which the lectures were mimeographed under the title 'Electromagnetic theory and its applications.' A third course was given in 1941-42, when the notes were revised under the present title."--Pref.
書誌注記"Bibliographical note": p. 513-514.