Even so, his retirement lasted only a few months. Music director Riccardo Muti valued his expertise and took him on tours and saw to it that he returned as a substitute, playing season after season. He last played with the orchestra in 1992.
Born in Philadelphia, Mr. Mogill graduated from the Philadelphia Musical Academy and Curtis Institute of Music. At 12, he played violin on a weekly radio show. He changed to viola when he entered Curtis, and he was 17 when his teacher recommended him for the new Robin Hood Dell Orchestra. Five years later, Leopold Stokowski engaged Mr. Mogill for the orchestra. He was for many years associate principal, and for 20 years was principal violist at the Robin Hood Dell.
He taught at Temple University, and continued to teach privately until his death. When the orchestra toured China in 1973, Mr. Mogill took copies of his published teaching materials, and developed a connection that brought several Chinese students here. When Mr. Mogill retired, the Chinese government sent him a pi'pa, an ornate lute.
He continued to publish studies for violists and was working on others when he died.
He is survived by his wife of 51 years, Beatrice; a daughter, Mara Selden; and a grandson.
Funeral services will be at 11 a.m. today at Goldsteins' Rosenberg's Raphael-Sacks, 6410 N. Broad St.