Someone tipped about half a hundredweight of washing detergent into the fountain in Trafalgar Square early yesterday morning. Soon after the fountains were on at 10 o'clock, a policeman noticed "a bit of a bubble," which was steadily beaten up into a froth, then a billowing, foaming blanket of lather. The news spread. In the afternoon, sightseers were queueing to be photographed against the Trafalgar-square foam-fountain. But at 4 p.m. the jets were turned off and workmen moved in to skim off the forth. But the question remained unanswered - who did it A policeman said: ''It could be that some bright spark wound up a party with a bubble-bath. December 29, 1952. (Photo by Daily Mirror).