We visited the home of Harriet Beecher Stowe, the author of Uncle Tom’s Cabin.
“Harriet Beecher Stowe” refers to the same person as “the author of Uncle Tom’s Cabin”. Hence, we would say that “the author of Uncle Tom’s Cabin” is in apposition to Harriet Beecher Stowe.
Jim, a student at Harvard, failed his entrance exam.
The professor of philosophy, Mr. Owen, was in a car accident and broke his femur, the largest bone in the human body.