Tastes change. By the mid century the Forth Bridge was no longer a triumph of the present, but a symbol of a previous triumphant age, still listed in children's books as the eighth wonder of the world, still printed on tea towels and shortbread tins, and still evoked with the liner Queen Mary as Scottish engineering at its gigantic best, but already failing quite to compete with the Comet airliner or the futuristic rumours of space travel coming from countries - the United States and USSR - that had displaced Britain as an innovator.
Today it is not so much a utility or a symbol as an issue. Railtrack can no longer afford to paint it regularly; the old analogy for the endless task - "like painting the Forth Bridge" - no longer applies. There have been arguments in the House of Commons, letters in the newspapers, protests from the humble, the great and the good. Railtrack remains unmoved. It says the structure is still as sound as ever (it was "over-engineered" in the wake of the Tay Bridge disaster of 1879) and the travelling public should not worry.
Nobody argues, however, with the fact that it looks a mess - stained, rusting, uncared for. Of all the many factors that will lose the Government its next byelection in Kinross and West Perthshire, the Forth Bridge will be in there somewhere, making its slight but symbolic contribution to the general unease about public squalor and neglect.