FRANKFURT AM MAIN has always struck me as a cold forbidding city. There is something aloof about it, like Berne, something even sinister, like Basel. Perhaps my aversion dates from the unhappy days when the French occupied the city as a punitive measure for some breach of the outlandish Reparations clauses of the Treaty. But for me, at any rate, Frankfurt will never have the attraction of other German cities. It has none of the glamour of Dresden. It lacks the vigour of Cologne.