_Answer._ [72]Because, however well a road may be kept up, there will always be shocks in running over it; these occur at the rail joints and especially when the ballasting of the ties is not quite perfect. These shocks affect the wheels first, and by them are transferred through the axle-boxes to the frame, the engine and the boiler. The faster the locomotive runs, the more powerful do they become, and therefore the more destructive to the engine and road, and consequently the faster a locomotive has to run the more perfect should be the arrangement of the springs. [72] The above answer and much of the material referring to springs has been translated from “Die Schule des Locomotivführers,” by Messrs. J. Brosius and R. Koch. If we strike repeatedly with a hammer on a rail, the latter is soon destroyed, while it can bear without damage a much greater weight than the hammer lying quietly on it. The axles, axle-boxes and wheels strike like a hammer on the rails at each shock, while the shock of the rest of the parts of the engine first reaches and bends the springs, but on the rails has only the effect of a load greater than usual resting on them. Another comparison will make still plainer the lessening by the springs of the injurious effect which the weight of the boiler, etc., exercises on the rails. A light blow with a hammer on a pane of glass is sufficient to shatter it. If, however, on the pane of glass is laid some elastic substance, such as india-rubber, and we strike on that, the force of the blow or the weight of the hammer must be considerably increased before producing the above-named effect. If the locomotive boiler is put in place of the hammer, the springs in place of the india-rubber, and the rails in place of the glass, the comparison will agree with the case above. From this consideration it will be seen how important it is to make the weights of the axles, axle-boxes and wheels as light as possible. QUESTION 280. _How are the driving-axle boxes arranged so that the weight of the engine will rest on springs?_ _Answer._ They are arranged so as to slide up and down in the jaws. Springs, _B_, _B′_, fig. 169, are then placed over the axle-boxes and above the frames. These springs rest on ~∩~-shaped saddles, _G′_, _G′_, which bear on the top of the axle-boxes. The frames are suspended to the ends of the springs by rods or bars, _g_, _g′_, _g_, _g′_, called _spring-hangers_. As the boiler and most of the other parts of the engine are fastened to the frames, their weight is suspended on the ends of the springs, which, being flexible, yield to the weight which they bear. QUESTION 281. _How are the frames protected from the wear of the axle-boxes which results from their sliding up and down in the jaws?_