So, what did I learn about Joseph Cornell in the course of the opening ?  That he was, shy, reticent, unknowable, never travelled to Europe except in his imagination, was obsessed by the nineteenth-century ballet.   Richard Feigen, who became his dealer, used to visit him in his small house on Utopia Parkway on the way back from Kennedy Airport.    He kept his collections of objects and memorabilia in the basement.   His great nephew sat on the beach with him but still did know him because a) he was unknowable b) he spent his time travelling obsessively in his imagination.