WEIGHT OF SQUARE IRON PER FOOT. ----------------------+----------------------- Side of Square. | Side of Square. Inch. lbs. | Inch. lbs. | ¼ ·208 | 2⅜ 18·8 ⅜ ·468 | 2½ 20·8 ½ ·833 | 2⅝ 22·9 ⅝ 1·30 | 2¾ 25·2 ¾ 1·87 | 2⅞ 27·5 ⅞ 2·55 | 3 30·0 1 3·33 | 3⅛ 32·5 1⅛ 4·21 | 3¼ 35·2 1¼ 5·20 | 3⅜ 37·9 1⅜ 6·30 | 3½ 40·3 1½ 7·50 | 3⅝ 43·8 1⅝ 8·80 | 3¾ 46·8 1¾ 10·2 | 4 53·3 1⅞ 11·7 | 4¼ 60·2 2 13·3 | 4½ 67·5 2⅛ 15·0 | 5 83·3 2¼ 16·8 | ----------------------+----------------------- CHAPTER VIII. SPRINGS. Springs in locomotive vehicles are the elastic substances interposed between the wheels and the load or passengers in order to intercept the concussion caused by running over an uneven road, or in meeting with any slight obstacle. A great variety of substances have been used for this purpose, such as leather, strips of hide, catgut, hempen cord, &c.; but these have now been totally superseded by metal springs, so that what is technically understood by the word “spring” is a plate or plates of tempered steel properly shaped to play in any required mode. It is very probable that the earliest steel springs were composed of only one plate of metal. This was very defective in its action; and unless it was restrained somewhat in the manner of the bow by the string, it was liable to break on being subjected to a sharp concussion. There is no hard and fast rule by which the spring-maker can be guided so as to proportion the strength and elasticity of his springs to the load they are required to bear; and even were such a rule in existence it would be practically useless, because the qualities of spring steel differ so much that what is known in mathematics as a “constant” could hardly be maintained. The only guide to the maker in this respect is observation of the working of certain springs under given loads, such springs being made of a certain quality of steel, and any peculiar features that appear should be carefully noted down for future reference and application. Springs are of two kinds, single and double; _i.e._ springs tapering in one direction from end to end, and those which taper in two opposite directions from a common centre, as in the ordinary elliptic spring. The process of making a spring is conducted in the following manner:—