The "Essai théorique et pratique" from 1809 is a fundamental contribution the establishment of a new organ music tradition after the French revolution. He present examples to every kind of organ piece in the new taste of Classizism. The "Essay" is therefore a school of organ composition as well as a school of organ playing. The pieces No. 1 to No.4 are very simple, but already the Duo No. 5 is not easy to play. With the Duo starts Lasceux a serie of large symphonic organ compositions. I think that the "Essai" was an inspiration for the collections of organ pieces by e. g. Batiste, Guilmant, Boellmann, Lefébure-Wély, Giguot etc.