Symphony No.51 in B-flat major, Hob. I:51

Sometimes described as "a concertante piece featuring the two horns, which are given parts of staggering difficulty." The second, slow, movement contains high notes for the first horn (including a notated F6 which is considered the highest note ever written for the horn) and very low notes for the second horn. Heartz has noted the character of the fourth movement as reminiscent of the French rondeau. The first contrasting section is an oboe solo in E♭ major and the second contrasting section is fortissimo and in G minor. The scherzo movement actually contains an even higher note for the first horn—a concert high B♭6[clarification needed] (the second movement contains a concert high A♭6, i.e. the previously discussed notated F6).[clarification needed]