In order to get all the advantages which a four-wheeled switching engine possesses in having its _whole_ weight on the driving-wheels, and at the same time avoid the disadvantages which result from a short wheel-base, and also from a varying amount of weight on the driving-wheels, a locomotive like that represented in Plate XV was designed by the writer with the whole weight of the boiler and machinery resting on the driving-wheels, and the water and fuel on a truck. By this means not only the objections to carrying the weight of the water on the driving-wheels is overcome, but at the same time the disadvantages arising from the short wheel-base of the switching locomotive, Plate IV, are also obviated. That is, all the _permanent weight_ of the boiler and machinery of such a locomotive rests on the driving-wheels, and is therefore all _adhesive weight_, as it is in the switching engine, and at the same time by extending the frame beyond the fire-box and placing the water-tank and fuel on this extension of the frame and supporting their weight on a truck, the engine has a wheel-base which is as long and as flexible as that of ordinary American engines, represented in Plates V, VI, VII, VIII and IX, and as the latter have only about _two-thirds_ of their weight on the driving-wheels, locomotives like that represented in Plate XV, of the same weight as the others, have fifty per cent. more adhesion, or they may be one-third lighter and have the same adhesion. As was explained in answer to Question 260, if an ordinary American locomotive runs backwards, that is, with the driving-wheels in front, the friction of their flanges against the rails on curves of short radius will be very excessive. To avoid this with locomotives of the design last described, they are run with the truck first, which, being at the opposite end of the boiler from the position which it usually occupies, reverses the position of the boiler and other parts relative to the motion of the engine. That is, the fire-box is then in front and the smoke-stack behind. Engines of this kind have been built and are now working and doing excellent service; but the prejudice which exists against running locomotives in the reverse direction to what has been customary seems to be the chief obstacle in the way of their use.