In 1877, Ruskin accused Whistler of 'flinging a pot of paint in the public's face'. Was he right? After all, Whistler always denied that the true function of art was to represent anything. If a painting does not represent, what is it, other than mere paint, flung in the public's face? Whistler's answer was simple: painting is music - or it is poetry. Georges Braque, half a century later, echoed Whistler's answer. So did Braque's friends Apollinaire...