New London — The Diderot String Quartet brought the crowd to its feet Friday at Connecticut College's Evans Hall after a masterful performance of Felix Mendelssohn's riveting String Quartet No. 2 in A Minor, Op. 13, played on period instruments in a style that the composer himself would have recognized.

The quartet, performing as part of the 37th Connecticut Early Music Festival, surely saved its best playing for the second half, highlighted by the earnest and earthy violin of Adriane Post and anchored by the brilliant cello work of Paul Dwyer. The quartet's other members, violinist Johanna Novom and violist Kyle Miller, were equally able collaborators as the group at turns swooned and bounced along with Mendelssohn's engaging melodies.

The dramatic, final presto section turned out to be an emotional roller coaster with a tricky faux ending that slid into a soft, sweet song of regret and then appeared to fade into nothingness — so much so that the audience of about 100 wasn't sure they'd reached the end.

Violist Miller, in an aside between pieces after intermission, said that the instruments being played that night were strung with gut, which makes a distinctive sound when players use a technique called portamento to slide from note to note. He said portamento directions were written into the music during Mendelssohn's time, and you still can hear the technique in older recordings of his work but it is rarely done today.

The technique seemed effortless and natural in the Mendelssohn works, which included the soulful Fugue in E Flat Major, Op. 81, No. 4, but stuck out a little in the first piece of the evening, Beethoven's String Quartet in F Major, Op. 18, No. 1. In this piece, Novom took the lead on violin, showing off her supple playing and mellow sound.

It all sounded a bit too controlled, however, and a little more exuberance such as occurred in the fun and jouncy scherzo movement would have brought the music more brilliantly to light.

The annual music festival concludes at 5 p.m. Sunday at Connecticut College's Evans Hall with an All Mendelssohn program featuring Stephanie Chase on violin with the Connecticut Early Music Ensemble, conducted by Ian Watson.

l.howard@theday.com