Throughout its history, it has been greatly helped by the prior existence of the steam traction engine. From these heavy and slow machines, suitable only for limited use in particular spheres, have been developed two very useful classes of lighter steam-propelled machines coming under the provisions of the Motor Car Acts. The first is the steam tractor, which is merely a small edition of the traction engine, able, on account of its lighter weight, to travel at considerably higher speeds. The other is the steam lorry, which is an extremely valuable machine for the carriage of anything up to about six tons of goods at speeds of about five miles per hour. From the five-ton steam lorry there has more recently developed a lighter type of steam vehicle in the shape of the three-ton lorry, generally running on rubber tyres, and so entitled legally to travel at much higher speeds. The great economy of steam motors made it absolutely necessary for the makers of internal combustion industrial vehicles to study every possibility of reducing operating costs. They had on their side advantages as regards higher speed possibilities and more complete independence of fuel supplies. The steam motor of ordinary type cannot be conveniently designed to carry with it fuel and water supplies adequate for very long journeys. On the other hand, the steamer has the great advantage of being able to exert tremendous power at low road speeds. The steam engine is more flexible and more capable of standing a heavy overload than the internal combustion engine. Even if it is brought almost to a standstill, it can go on applying the full steam pressure behind its piston during every stroke. Given adequate supplies of fuel and water, it is an admirable and very economical machine for all sorts of rough and heavy work. Curiously enough, the steam lorry and the steam tractor have been essentially British developments, and as such they have done much to bring the British industrial petrol vehicle up to its present high standard of perfection.