If one end is sharply pressed in, a compression can be seen running along the spring.
Thus a push or a compression of the X air is transmitted onwards in the direction OX.
The compression members are of timber, except the struts and bottom chord panels next the river piers, which are of steel.
Nearly related is the extinct family Lophiodontidae (inclusive of the American Helaletidae), in which both the upper and lower first premolar may be absent, while the upper molars present a more rhinoceros-like form, owing to the lateral compression and consequent lengthening of the outer columns, of which the hinder is bent somewhat inwards and is more or less concave externally, thus forming a more complete outer wall.
The concrete not only affords much of the strength to resist compression, but effectively protects the steel from corrosion.