Various modifications have been made in the hydraulic forms. In place of steam, electricity was introduced to control the hydraulic operation. Again, an electric motor has been invented to be placed on the car itself, with connected gearing engaging rack bars in the well. Elevators have been contrived automatically controlled by switch mechanisms on the landings; and in connection with the electric motor safety devices are used to break the motor circuit and thus stop the car the moment the elevator door is opened; and there are devices to break the circuit and stop the car at once, should an obstruction, the foot for instance, be accidentally thrust out into the path of the car frame. Columns of water and of air have been so arranged that should the car fall the fall will be broken by the water or air cushion made to yield gradually to the pressure. So many safety devices have been invented that there is now no excuse for accidents. They result by a criminal neglect of builders or engineers to provide themselves with such devices, or by a most ignorant or careless management and operation of simple actuating mechanisms. Between 1880 and 1890 there was great activity in the invention of what is known as store service conveyors. One of the earliest forms, and one which had been partly selected from other arts, was to suspend from a rigid frame work connected to the floor, roof, or side of the building, a long platform in the direction through the building it was desired the road to run, giving this platform a slight inclination. On this platform were placed tracks, and from the tracks were suspended trucks, baskets, or other merchandise receptacles, having wheels resting on and adapted to roll on the tracks. Double or single tracks could be provided as desired. The cars ran on these tracks by gravity, and considerable ingenuity was displayed in the feature alone of providing the out-going and returning inclined tracks; in hand straps and levers for raising and lowering the carriage, part or all of it, to or from the tracks, and in buffers to break the force of the blow of the carriages when arriving at their stopping places.