Hence the moment at any section _X_ in the panel in question will be [ _l-x z′_] _M = Rx-R₅_{_z_′-(_z-x_)} = _g_[ ---- _z_-(_z-z′ + p-x_)---]. (_e_) [ _l p_ ] Remembering that _z-z′_ is a constant quantity, it is at once clear that the preceding expression is the equation of a straight line, with _M_ and _z_ or _z′_ the variables. If _z′ = 0_, equation (_e_) becomes identical with equation (_a_), while if _z′ = p_, it becomes identical with equation (_b_). Hence the influence line for the panel in which the load is placed, as 5-6, is the straight line _KL_. It is manifest that when the load _g_ is in any other panel than that in which the section _X_ is located, the effect of the two reactions at the extremities of that panel will be precisely the same at the section as the weight itself acting along its own line of action. Hence the two portions _AK_ and _BL_ of the influence line are to be constructed as if the load were applied directly to the beam or truss, and in the manner already shown. The complete influence line will then be _AKLB_, and it shows that the existence of the panel slightly reduces the bending at any section within its limits. The panel 5-6, as treated, is that of a beam in which the bending moment will, in general, vary from point to point. If _AB_ were a truss, however, _X_ would always be taken at a panel-point, and no intercept between panel-points, as 5 and 6, would be considered. =101. Influence Lines for Shears both for Beams and Trusses.=—The influence lines for shears in a simple beam, supported at each end, can be drawn in the manner shown in Fig. 25_a_. In that figure _AB_ represents a non-continuous beam with span _l_ supported from _A_. The reaction at _A_ will be _l-z_ _R_ = ----- _g_. _l_ [Illustration: FIG. 25_a_.—Shear in a Simple Beam.] Let _X_ be the section at which the shear for various positions of _g_ is to be found. When _g_ is placed at any point between _A_ and _X_ the shear _S_ at the latter point will be _z_ _S_ = _R_ = _g_ = -_g_ ----; (_f_) _l_ but when the load is placed between _B_ and _X_ the shear becomes _z_ _S_′ = _R_ = _g-g_ ----. (_h_) _l_