3. It must be well supplied with safety-valves and pressure-gauges.
4. It must not exceed fifteen feet in height.
5. It must rest on springs.
6. It must be able (if weighing six tons) to draw twenty tons continuously ten miles per hour.
7. It must not cost more than $2,750.
8. The boiler must stand a pressure, when tested, of 150 pounds per square inch.
9. It must be ready for trial October 1, 1829.
The publication of these conditions and the offer of the prize excited great interest, and caused no small amount of comment.[11] The Stephensons at once began the construction of "The Rocket," without doubt the most famous locomotive ever built. The improved feature it was to have was increased heating surface, so that without increased weight it could generate more steam. This was effected by putting fire-tubes through the water in the boiler. Boiler-tubes had already been used by different people, and some of Stephenson's locomotives which he had sent to France had been fitted with tubes. At the suggestion of Mr. James Booth, Stephenson decided to use a large number of tubes. Modern boilers have smaller tubes and more of them, but "The Rocket" was the first to typify the modern multitubular boiler. In other respects "The Rocket" was like Stephenson's other locomotives built ten or twelve years earlier.
A brief description of "The Rocket" will not be out of place: The boiler was 6 feet long, 3 feet 4 inches in diameter, and was furnished with 25 copper tubes 3 inches in diameter. The fire-box was at the rear end of the boiler, 2 feet wide and 3 feet high, surrounded by water. The cylinders were high on the sides, pointing down to the forward wheels, which were the only drivers. Stephenson had used coupling rods between two sets of "drivers," but "The Rocket" was made for speed chiefly. Its weight when furnished with water was only four and a half tons! On trial at Killingworth "The Rocket" worked finely and its capacity for steam was marvellous. It was sent by wagon to Carlisle and by boat to Liverpool.
On the day set for the trial there were four engines on hand: 1. The "Novelty," built by young Ericsson, who afterward in New York built the famous "Monitor." 2. The "Sanspareil," by Timothy Hackworth. 3. The "Perseverance," by a Mr. Burstall. 4. "The Rocket," by Stephenson and Booth.