The use of a portable mechanical " humper " is shown in Fig. 296. Such " humpers " are inserted at any convenient point of the track, and are generally inclined at an angle of 45J , with an easy curve at either terminal where the cases are gently received at the lower level and equally gently passed on at the upper end, in both cases from and on to roller runways: The " humper " provides sufficient motive power to permit the packages to travel to the end, or, as it is technically termed, " renews the gradient. "