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.
If A t A, are the cross sections of the tension and compression flanges or chords, and h the distance between their mass centres, then on the assumption that they resist all the direct horizontal forces the total stress on each flange is Ht=H,=M/h and the intensity of stress of tension or compression is f t = M/Ath, f c = M/Ach.