An important exhibition of work by Mary Cassatt (1844-1926) has opened at the Philadelphia Museum of Art and runs until 8th September. She was born in Pennsylvania but went to Paris and was invited by Edgar Degas to join the group of artists who came to be known as the Impressionists. She is widely known for her mother and child themes as in 'Mother and Child' (1880, private collection), but this 'polemical' show presents her as a far more complex and radical artist.