SECTION OF THE FIRST BOILER IN USE.
"Don't speak of thirty miles an hour," rejoined Stephenson; "I should not dare talk about such a thing aloud." For I suppose he could hardly forget how Parliament committees had branded him as a fool and a madman for broaching such beliefs.
SECTION OF A TUBULAR BOILER.
The improved boiler was what is called a multi-tubular boiler. You do not understand that, I suppose. An iron boiler is cast, six feet long, and three feet and a third in diameter. It is to be filled half full of water. Through this lower half there run twenty-five copper tubes, each about three inches in diameter, open at one end to the fire, through which the heat passes to the chimney at the other end. You see this would present a great deal of heating surface to the water, causing it to boil and steam off with great rapidity. The invention was not a sudden growth, as no inventions are. Fire-tubes serving this use started in several fertile minds about the same time, and several persons claimed the honour of the invention; but it was Stephenson's practical mind which put it into good working order and made it available. For he told Robert to try it in his new locomotive.
He did. The tubes were of copper, manufactured by a Newcastle coppersmith, and carefully inserted into the ends of the boiler by screws. Water was put into the boiler, and in order to be sure there was no leakage, a pressure was put on the water; when, lo, the water squirted out at every screw, and the factory floor was deluged! Poor Robert was in despair. He sat down and wrote to his father that the whole thing was a failure.
A failure indeed! Back came a letter by the next post telling him to "go ahead and try again!" The letter, moreover, suggested a remedy for the disaster—fastening the tubes into the boiler by fitting them snugly into holes bored for the purpose, and soldering up the edges. And it proved to be precisely what Robert himself had thought of, after the first bitter wave of disappointment had subsided. So he took heart and went to work again. Success crowned his efforts. A heavy pressure was put on the water, and not a drop oozed out. The boiler was completely water-tight.
This is precisely the kind of boiler now in use: some have fifty tubes; the largest engines one hundred and fifty.
THE FAILURE.