Emily Cornelius began studying the violin when she was 10, rather late in life for someone who seems headed for a distinguished career as a violinist.

Itzhak Perlman began on the instrument when he was 4--a fairly common age for solo musicians who are destined to become world-class. He once told me that it takes at least six months before a beginning violinist can produce a sound that he or she finds bearable, another year or two before one's dearest friends and relatives can bear to listen even for a few minutes, and a long, long time after that before a public performance becomes a realistic possibility. Ravi Shankar found the time requirements even longer for the sitar and warned that no matter how hard you work or for how many years, you may never satisfy your teacher.

By these standards, Cornelius has been moving very fast. On Sunday, now 15, she gave a recital that delighted a standing-room audience at the Lyceum in Alexandria.

It also (and this may be the acid test) clearly delighted her teacher, National Symphony Orchestra violinist Peter Haase, who joined her as co-soloist in the opening number, Antonio Vivaldi's Concerto in A minor for two violins, Op. 3, No. 8.

The performance testified to a smooth, productive student-teacher relationship, from the precisely coordinated unison playing in the first movement to the eloquent and technically impressive dialogues of the slow movement and finale. The two minds engaged in this performance clearly were thinking as one.

Actually, there were three minds; pianist Darya Gabay handled the orchestral part of this composition with intelligence, fine technique and a commendable grasp of appropriate phrasing and dynamics. Her participation was exemplary throughout the program, except in the second selection, the Adagio and Fugue from Bach's Sonata in G minor, where the violinist, unaccompanied, faced and fulfilled a twofold challenge.

It is a tough assignment, on a melodic instrument designed to play one note at a time, simply to produce all the notes Bach set down: chords in the Adagio; two simultaneous, interwoven melodic lines in the fugue. Cornelius not only managed that, she also triumphed in the further challenge of making it a cohesive and compelling musical experience, not a sort of gymnastic exercise.

The third selection, with Gabay back as a partner, was an early piece by Beethoven, the Sonata in D for violin and piano, Op. 12, No. 1, music poised between the graceful lyric style of the late 18th century and the more dramatic moods of early romanticism.

The partnership of violin and piano is all-important in this, and it is different from the partnership of two violins in the Vivaldi concerto because the violin and piano belong to such different musical families. This is true chamber music in a way that the Vivaldi and Bach pieces are not; the point at issue was, in a sense, the violinist's maturity in a performing partnership where the other instrument often has the initiative; Beethoven, who was a pianist, published the sonata "for piano with violin accompaniment." The partners played with a fine sense of the music's delicate and shifting perspectives.

For the second half of the program, Cornelius played two brilliant tests of violin virtuosity, the first movement of Sibelius's Violin Concerto and Sarasate's technically dazzling Caprice Basque, separated by the gentler, more lyric Sicilienne of Maria Theresia von Paradis.

Whether you judge by the fiendishly difficult left-hand pizzicatos and brilliant dance rhythms of Sarasate or the long, complex lines and impassioned dynamics of Sibelius, Cornelius gave an impressive account of the music. She is now the concertmaster of the Richmond Symphony Youth Orchestra, a member of the National Symphony Youth Program and a recent winner in the Friday Morning Music Club's Neva Greenwood String Competition. This fall, she will make solo appearances with the Richmond Symphony and the Williamsburg Sympnonia--remarkable achievements after only five years of study.

Free solo recitals sponsored by the Mount Vernon Chamber Orchestra Association will be given in the Lyceum at 3 p.m. every Sunday through mid-September, except Labor Day weekend.