<P> Ptolemy also wrote influential work Harmonics on music theory . After criticizing the approaches of his predecessors, Ptolemy argued for basing musical intervals on mathematical ratios (in contrast to the followers of Aristoxenus) backed up by empirical observation (in contrast to the over-theoretical approach of the Pythagoreans). He presented his own divisions of the tetrachord and the octave, which he derived with the help of a monochord . Ptolemy's astronomical interests also appeared in a discussion of the music of the spheres . </P> <P> Tributes to Ptolemy include Ptolemaeus crater on the Moon and Ptolemaeus crater on Mars . </P> <P> Ahmed Zewail (Arabic: أحمد زويل ‎) (born February 26, 1946) is an Egyptian chemist, and the winner of the 1999 Nobel Prize in Chemistry for his work on femtochemistry . Born in Damanhur (60 km south - east of Alexandria) and raised in Disuq, he moved to the United States to complete his PhD at the University of Pennsylvania . He was awarded a faculty appointment at Caltech in 1976, where he has remained since . </P> <P> Zewail's key work has been as the pioneer of femtochemistry . He developed a method using a rapid laser technique (consisting of ultrashort laser flashes), which allows the description of reactions at the atomic level . It can be viewed as a highly sophisticated form of flash photography . </P>

How was the development of egypts culture influenced by its physical geography