Harvard Extension School is making select content available for free to iTunes users. Free public access is being offered to video previews of 15 of the 50 distance education courses that are available this spring from the university. Previews are in the fields of computer science, management, environmental science, history and the liberal arts. Audio of each complete two-hour introductory lecture is also available for downloading. Course previews include Harvard professor Mikael Adolphson’s Japan: Tradition and Transformation; Harvard professor Shaye J. D. Cohen’s A Thematic Introduction to the Hebrew Bible; Harvard’s Scott Bradner’s Advanced Topics in Data Networking, and Suffolk University professor Robert J. Allison’s The History of Boston.