Dance is one of the hardest art forms to preserve for posterity. Symphonies can be rendered as sheet music or captured on recordings, plays have scripts and operas have librettos — but old dance performances often exist only on videos, which tend to be few in number and prone to fading. Tom Whitehead of Temple University Libraries is spearheading a dance archive at Temple. Whitehead is taking on the daunting task of digitizing material from a half dozen obsolete video formats.