To those who appreciate music but do not create it, the whole process of musical composition is a major mystery. And usually the artist himself cannot explain it. But there is on record the story of one man, the great Frenchman Charles Camille Sassas, who knew that death itself had produced his requiem. In 1871, Sassas was known merely as a brilliant young virtuoso. He held the post of organist at the Madeleine in Paris. On a certain day in January of that year, when the Fra…