Fig. 76. Car-spring
"There are many kinds of springs, but I will only talk of steel or other metal springs; and even then must limit myself to a few. The carriage or laminated spring is probably the most in use, as it is an important factor in the construction of all classes of railway trucks and carriages, locomotives, automobiles, road carriages and light wagons of all kinds. These are also much used in the manufacture of invalids' chairs, children's perambulators, and many other things. The springs used in the construction of the largest locomotives are big affairs and often weigh over 500 pounds. These are bearing springs and carry the whole weight of engine and boiler. There are, of course, a number of these springs to each engine. Springs on the coaches and carriages are somewhat lighter and more flexible than those on the heavier trucks. The double spring, shown at [Fig. 76], is known in railroad parlance as a 'draw-spring.' One of these is secured at each end of the car, and used to attach or couple the cars together, or to attach the engine to the train, the object being to lessen the bump or impact of the blow when the engine and cars come together. The effect is the same when the engine starts a train; the springs in the first car draw out, then the springs on the second car do likewise, and this causes the load of the whole train to fall on the engine gradually, a matter of great importance in railway economy. If it were not for bearing springs on the trucks and carriages, it would be almost impossible to use railroads for passenger traffic or for carrying fine goods, as the jolting and pounding on the iron rails would shake things to pieces, destroy the carriages, and pound the roadbed and bridges to bits in a very short time. Now, by the aid of steel springs, you ride in a Pullman as smoothly almost as in a boat, so you see how useful springs are to mankind.
Fig. 77. Cross-bow spring
"There are many kinds of bearing springs, but all are built in the same manner, of steel leaves, made of different dimensions to suit conditions. As you will see in the diagram, the sheets of steel are laid over each other, like the scales of a fish, and made shorter as they approach the top. All the leaves are fastened together by having an iron buckle driven onto the middle, as shown, while hot, and when this cools, it shrinks and clasps the whole so tight it cannot be taken off until heated or cut. I could tell you of many other kinds of springs—watch springs, gun springs, trap springs, spiral springs—used for various purposes, but I will end this subject by describing to you something you can make for yourself, if you wish; namely, a cross-bow, which is very simple. I make on the blackboard a diagram, ([Fig. 77]), with A representing the stock, 5 feet long; B, the bender, 6 feet long, which should be made in four pieces. The front piece should be 3⁄4 inch thick, the three inner pieces 1⁄2 inch thick. C are brass ferrules to keep the leaves of the bender from shifting; D the string, which should be very strong. The bender should be cut out of straight well-seasoned ash, rock elm, or hickory. Instead of brass ferrules, strong brass or copper wire can be used, properly twisted at the joints.
Fig. 78. Gyroscope