Then the figure is (usually) the sum of two trapezoids F on base **AE**, and its area can be calculated as in § 24.

The wave at a depth x is represented analytically by the equation 0 - 0 0 = **Ae** mx sin (21rnt - mx).

A cord has one end made fast a to and wrapped round the barrel **AE**; it passes from A under the sheave FG, and has the other end wrapped round and made fast to the barrel BD.

The vertical distance above the line ab of any point in the dotted line dc is proportional to the vertical component of the compressive stress on the line ale assumed to vary uniformly from face to face, and similarly the vertical distance of any point in the3-dot-and-dash line **ae** above the line ab is proportional to the vertical component of the stress determined experimentally.