Although photography is a "visual medium", it is not a "purely visual" medium. I am not alluding simply to the fact that we rarely see a photograph in use which is not accompanied by writing (albeit this is a highly significant fact), even the uncap-tioned "art" photograph, framed and isolated on the gallery wall, is invaded by language in the very moment it is looked at: in memory, in association, snatches of words and images continually intermingle and exchange one for the other. It will be objected that this is indistinct and insignificant background noise to our primary act of seeing. If I may be excused a physiological analogy, the murmur of the circulation of the blood is even more indistinct, but no less important for that.