The thin membrane of darkness belied the turbulence that lay beneath as we drifted down the river, the eddies and swirls on the surface softly luring me into a trance. The sky burned a brilliant vermillion as the sun set over the sands of the Sahara, casting the tomb of Aga Kahn in a long blue shadow. As we drifted lazily down the Cataracts of the Nile, the pilot of our felucca ducked under the foredeck and returned with a large tambourine; his deep voice now keeping time to an ancient Nubian beat that echoes off the massive boulders surrounding us.  He appears lost in song; yet, as if unknowingly, maneuvers a perfect tack of the vessel with its massive sail.  At first, we…