'More than 20 years ago I was called upon by friends, artists, and aficionados to write about fingerings for the violoncello,'' then-famous Berlin cellist Jean-Louis Duport thus opens his ''Essai'' from 1806, dedicated to ''Professeurs de Violoncelle''. His methodology revolutionized cello technique, and the 21 etudes printed in its appendix are still regarded today as perhaps the most important set of studies for all budding cellists. Modelled after the volumes of etudes for violin, Henle is al