Early in the first movement of a little-known Mozart piece in the Handel and Haydn Society’s concert at Symphony Hall on Friday, it was clear something special was going on. The conductor, the respected British Mozart specialist Jane Glover, seemed to be a Harry Potter character generating electricity with her hands, and the musicians were smiling and alert, as if receiving gentle shocks. This was music-making as a controlled blaze.
It was a brilliant idea to take the four entr’actes to “Thamos, King of Egypt’’ and stitch them together (minus choruses) to create a virtual lost symphony. “Thamos’’ was an experimental early work, revised by Mozart in 1779 as incidental music for a play (Mozart’s only such effort). It is full of the novel orchestra devices he had observed on his recent European tour - the sforzatos and crescendos, the coups d’archet (string attacks), the offbeat accents and sharp cutoffs. The orchestra’s period instruments created beautiful and surprising blends of sounds and allowed for a lovely interplay of voices, as string bow-strokes sounded remarkably like woodwind accents, and vice versa.