Arabesque No. 1 is generally the more well-known of the two, being a readily-recognized piece of classical music and making its way into such things as phone ringtones.
This arabesque is in the key of E major. The piece begins with parallelism of triads in first inversion, a composition technique very much used by Debussy and other Impressionists which traces back to the tradition of fauxbourdon. It leads into a larger section which begins with a left hand arpeggio in E major and a descending right hand E major pentatonic progression.
The second quieter B section is in A major, starting with a gesture (E-D-E-C♯), briefly passing through E major, returning to A major and ending with a bold pronouncement of the E-D-E-C♯ gesture, but transposed to the key of C major and played forte.
In the middle of the recapitulation of the A section, the music moves to a higher register and descends, followed by a large pentatonic scale ascending and descending, and resolving back to E major.