This sampling of photographs, drawings, manuscripts and illustrations from the collections of Library of Congress illuminates in fascinating detail some of the people and works of more than two centuries of classical music.  Here are Beethoven and Bach, Debussy and Lili Boulanger, Horowitz and Rachmaninoff; La Boheme, and Mendelssohn’s rendering of the Gewandhaus; Stravinsky caricatured by the master Covarrubias; instruments from a nineteenth-century French encyclopedia; and a letter in which the fourteen-year-old Mozart sends thousands of kisses to his mother. Thirty color and black-and-white reproductions.