THE HORSE archers of ancient Iran had a trick known as the Parthian shot. When retreating after a charge they were able to twist their bodies around in the saddle and loose a final salvo. That is not a bad description of the announcement made on February 8th by the controllers of the Joint European Torus (JET), a fusion experiment at Culham, England. After 40 years of operation, JET shut up shop in December. But the result of one of its final runs, conducted on October 3rd of last year, makes an excellent Parthian shot.