What They’re Watching

YouTube, with its view-count ticker, has become a useful tool for determining the popularity of an online video — whether it has gone “viral,” as the kids say. Atop YouTube’s list of most-popular course lectures (as of April 1) is “Justice,” Michael J. Sandel’s legendary philosophy class. The course’s videos also happen to be the only ones produced for public television. The Top 10 videos are the first lecture in a series, except No. 6, which is smack in the middle of a course on search engines. That lecture may have been boosted by a guest — Sergey Brin, the co-founder of Google.

1. Moral Reasoning 22: Justice Harvard

2. Integrative Biology 131: General Human Anatomy University of California, Berkeley

3. Physics 10: Physics for Future Presidents University of California, Berkeley

4. Physics 1: Classical Mechanics M.I.T.

5. Introduction to Basic Electronics Indian Institutes of Technology

6. SIMS 141: Search Engines: Technology, Society and Business University of California, Berkeley

7. Computer Science 106A: Programming Methodology Stanford

8. Mathematics 18.03: Differential Equations M.I.T.

9. Modern Theoretical Physics: Einstein Stanford Continuing Studies

10. Math 18.06: Linear Algebra M.I.T.