THE PALL MALL MAGAZINE
On this first trial—as in most since—I used hydrogen gas. Undoubtedly, when mixed with air, it is tremendously inflammable. But it must first mix with air. All my little balloon models are kept filled with hydrogen ; and, so filled, I have more than once amused myself by burning inside them, not their hydrogen but the oxygen of the atmosphere. All one has to do is to insert in the balloon model a little tube to furnish a jet of the room's atmosphere from an air-pump, and light it with the electric spark. Similarly, should a pin-prick have made ever so slight a vent in my air-ship balloon, the interior pressure would have sent out into the atmosphere a long thin stream of hydrogen that might have ignited—had there been any flame near enough to do it. But there was none.
The balloon house at Monaco.
This was the problem. My motor did undoubtedly send out flames for, say, half a yard around it. They were, however, mere flames, not still-burning products of incomplete combustion like the sparks of a steam-engine fed by coal. This admitted, how was the fact that I had a mass of hydrogen unmixed with air and well secured in a tight envelope so high above the motor to prove dangerous ?
Turning the matter over and over in my mind, I could see but one dangerous possibility from fire. This was the possibility of the petroleum reservoir itself taking fire by a retour de flamme from the motor. During five years, I may here say in passing, I enjoyed complete immunity from the retour de flamme. Then, in the same week in which Mr. Vanderbilt burned himself so severely, on July 6th, 1903, the same accident overtook me in my little " No. 9 " runabout air-ship, just as I was crossing the Seine to land on the Ile de Puteaux. I promptly extinguished the flame with my Panama hat... without other incident.
For reasons like these I went up on my first air-ship trip without fear of fire ; but not without doubt of a possible explosion due to insufficient working of my balloon's escape-valves. Should such a " cold" explosion occur, doubtless the flame-spitting motor would ignite the mass of mixed hydrogen and air that would surround me. But it would have no decisive influence on the result. The " cold" explosion itself would doubtless be sufficient....
Now, after five years of experience, and in spite of the retour de flamme above the Ile de Puteaux, I continue to regard the danger from fire as practically nil ; but the possibility of a " cold" explosion remains always with me, and I must continue to purchase immunity from it at the cost of vigilant attention to my gas escape-valves. Indeed, the possibility of the thing is greater technically now than in the early days which I describe. My first air-ship was not built for speed : consequently it needed very little interior pressure to preserve the shape of its balloon. Now that I have great speed, as in my "No. 7," I must have enormous
