Under the influence of civil engineering construction the part played by shear in the deformation of beams is usually neglected. In aircraft construction, where weight is important, the approximation is sometimes rough. It is shown that, in I-beams, it is simple to take the deformation due to shear into account, and it appears due chiefly not to elementary deformations distributed along the length, but to discontinuities in the slope wherever there is a concentrated load, namely, at the supports.