Leonard Bernstein performing Rhapsody in Blue

Royal Albert Hall, 1976: A unique concert with Leonard Bernstein as the conductor and the Piano Master, performing George Gershwin's Rhapsody in Blue.

The famous clarinet opening of Rhapsody in Blue.

The opening of Rhapsody in Blue is written as a clarinet trill followed by a legato 17-note rising diatonic scale. During a rehearsal, Whiteman's virtuoso clarinetist, Ross Gorman, rendered the upper portion of the scale as a captivating (and fully trombone-like) glissando: Gershwin heard it and insisted that it be repeated in the performance.[19] An American Heritage columnist called it the "famous opening clarinet glissando... that has become as familiar as the start of Beethoven’s Fifth."[14] The effect is produced by gradually opening the left-hand tone-holes on the clarinet during the passage from the last concert F (or earlier if possible, thus employing the right hand as well) to the top concert B-flat, adjusting the embouchure to smoothly control the continuously rising pitch. This effect has now become standard performance practice for the work.
http://en.wikipedia.org/wiki/Rhapsody_in_Blue#Analysis