Hilma af Klint's daring abstractions exert a mystical magnetismWhen Swedish artist Hilma af Klint died in 1944 at the age of 81, she left behind more than 1,000 paintings and works on paper that she had kept largely private during her lifetime. Believing the world was not yet ready for her art, she stipulated that it should remain unseen for another 20 years. But only in recent decades has the public had a chance to reckon with af Klint's radically abstract painting practice—