This week two nails were hammered into the coffin of the internal-combustion engine. The first came when Toyota and General Motors, which between them make a quarter of world's cars, signed a pact to develop alternatives. These include battery-powered cars, "hybrid" vehicles that have both electric and petrol engines, and - most significantly - vehicles powered by fuel cells. The second was the result of an alliance between DaimlerChrysler and Ford and Ballard Power Systems, a Canadian firm that has been developing fuel cells for use in vehicles for several years.