Meusnier, a French general, first conceived the idea of compensating for loss of gas by carrying an air bag inside the balloon, in order to maintain the full expansion of the envelope. The brothers Robert constructed the first balloon in which this was tried and placed the air bag near the neck of the balloon which was intended to be driven by oars, and steered by a rudder. A violent swirl of wind which was encountered on the first ascent tore away the oars and rudder and broke the ropes which held the air bag in position; the bag fell into the opening of the neck and stopped it up, preventing the escape of gas under expansion. The Duc de Chartres, who was aboard, realised the extreme danger of the envelope bursting as the balloon ascended, and at 16,000 feet he thrust a staff through the envelope--another account says that he slit it with his sword--and thus prevented disaster. The descent after this rip in the fabric was swift, but the passengers got off without injury in the landing.