In 1961, Arnold Kent of England had the idea of fitting inflatable cushions in front of the occupants of a car. They were stowed until a collision caused them to be inflated automatically from a container of compressed air or inert gas. Three or four years later this idea was taken up by Eaton, Yale and Towne in America and some complex air bag systems evolved, these were the start of something that would be greatly developed and would be fitted to all models of new Rolls Royce for sale. The air cushions were stored in the steering wheel hub, under the fascia and in the backs of the front seats. Triggering devices located in the bumpers inflated the bags from compressed gas bottles, sometimes through a frangible diaphragm broken by a small cartridge. To prevent an air pressure build up within the car body, which could cause injuries, one scheme included a further explosive charge to blow out the windscreen. Another form of passive restraint which does not need any action by the passenger is the self applying seat belt. In 1966, Porsche developed a shoulder and lap strap belt with two ends attached to the rear of the door and the third to an arm between the seats, this was fitted for a period to some new Porsche cars, but was later thought to be quite ineffective, so was discontinued. As the door shut, the belt moved to its correct position and was tightened by rearward movement of the arm. In other designs one of the belt mountings in the door moved to set the belt. The belt ends were moved by electric motors having limit switches that prevented engine starting unless the belts were fixed. Realizing that the restraint systems gave little or no protection to small children, Jean Ames of England produced a special child seat and harness in 1962. This padded seat was held on the rear seat by straps passing to strong points in the car body. A full harness retained the child comfortably and safely. Later development included a system allowing for child growth from cot to adult by changing the straps. While these restraint systems save the occupants from the forward acceleration of front impacts, they gave no protection from the effects of those from the rear. In the mid 1960s, Saab and Volvo of Sweden, and Bentley Motors of England began to fit headrests to the tops of the front seats. These prevented “whiplash” injuries where the head was suddenly accelerated backwards over the back of the seat. These built in head rests were made narrower than the seat back to allow some rearward vision for the driver and forward vision for the rear passengers.