Stephenson's "Rocket" - 1829.
The boiler of this engine was cylindrical in form, with flat ends, it was six feet in length, and three feet diameter; the upper part of the boiler was used as a reservoir for steam, the lower half being filled with water; through this lower part, twenty-five copper tubes, three inches in diameter, extended with both ends open, one presented to the furnace and the other opening into the chimney. The firebox, two feet long and three feet high, attached immediately behind the boiler, was also surrounded by water. The cylinders, two in number, were placed on each side of the boiler in an oblique position, the one end being nearly level with the top of the boiler and the other end pointing toward the centre of the foremost pair of driving wheels with which the connection was made with the piston rod by a pin to the outside of the wheel. The Rocket with its load of water weighed only 4_ tons and was supported on four wheels not coupled.
A further description of The Rocket is given in A History Of The Growth Of The Steam-Engine by Robert H. Thurston.