The Danish Ballet mounts a Bournonville Festival. “As dead geniuses go—especially those whose work, being in dance, is essentially ephemeral—August Bournonville (1805-1879) has done pretty well. The legacies of George Balanchine, Frederick Ashton, Martha Graham—all a century younger than the Danish choreographer—are eroding at an alarmingly faster rate than his, despite the fact that modern times have delivered the preservation tools of sophisticated dance notation (Bournonville used a crude—if singularly effective—personal one), film, and videotape.”