His father discovered his musical talents early on, and from the age of 6 Arthur studied with the Dutch-born violinist and composer Martinus van Gelder (1854–1941).
Later, Hartmann would adopt "Martinus" as a middle name in his teacher's honor.Uncle to writer/artist Alfred Bendiner (1899–1963)
Author of "Claude Debussy as I Knew Him' and Other Writings of Arthur Hartmann"