Wat Piston, who last year (to receive) a prize for his invention of the Piston Gas Fire, now (to invent) a new type of steam engine When I (to interview) him recently at his home in York he (to tell) me about it. 'I (to get) the idea from some work I (to do) many years ago for the Steam Preservation Society', he (to say). 'For years now, people (to think) that there is no future for steam as an everyday source of power. Indeed, after the railways (to stop) using steam engines people almost (to forget) about it .Yet steam (to be) the main source of power in this country for over 150 years, until World War Two. I always (to believe) that steam has a future as well as a past.' Piston is a remarkable man, who (to have) an unusual career. He (to leave) school when he was 15, and (not to have) any training as an engineer until he was 35. Yet now he (to design) a steam engine more efficient than any of the engines that (to be built) during the great age of steam. 'The engineers of the past (to be) great men', he says. 'But they (not to develop) the best possible steam engine. The techniques I (to invent) will change that.'