The boiler is of the flash type; that is, it carries no water ordinarily, but when the engine is in operation, a pump injects into the boiler at each stroke of the engine as much water as may be required to generate the steam necessary to propel the vehicle; the instant the water enters the boiler it is converted into steam. As the amount of steam is proportional to the amount of water, it can be seen that by regulating the water supply, the power of the engine and thereby the speed of the carriage, can be controlled. This is the method actually employed to control the speed. In starting, a handle is moved which connects the engine, the boiler and the pump in the proper relation; and while under way the velocity is varied by the manipulation of a lever which controls the amount of water injected into the boiler. The fuel used is kerosene, which is vaporized and then fed into a properly constructed burner. The amount of oil supplied to the burner is regulated by the same lever that regulates the supply of water, so that both are increased or reduced in the proper proportion. The boiler is constructed of a number of steel tubes, which are about two and a half inches in diameter, and from three eighths to half an inch thick. These tubes are pressed into the form shown in Fig. 13, the dark line in the section marked A representing the interior space. A number of tubes collapsed in this form and bent into the shape B, are assembled as shown at C. The number of tubes depends upon the capacity of the boiler. As the tubes are very thick, they can, without any danger of bursting, be heated to so high a temperature that the water injected into them is at once turned into steam. In Fig. 12 it will be seen that the engine is located under the body of the carriage between the two axles, and that motion is imparted to the hind wheels by means of chains and sprocket wheels. The boiler is located at the back of the vehicle, the lower part projecting some distance below the rear axle. A small smoke stack at the rear of the body allows the gases of combustion to escape. Between the front wheels, a compact condenser is located, and into this the steam from the engine is exhausted. The condenser serves two purposes; it recovers a portion of the water that would otherwise escape into the air, and thus increases the distance the carriage can run without a new supply, and at the same time it lessens the noise produced by the exhaust, and also the volume of steam escaping into the atmosphere, which in cold or rainy weather becomes plainly visible. [Illustration: FIG. 14. AN AMERICAN STEAM CARRIAGE OF 1900.]