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 heaviest known engine, counting the weight of its battery. Indeed, I have so little patience with the idea that I shall say no more about it except to repeat what Mr Edison said to me on this head in April 1902: "You have done well," he said, "to choose the petroleum motor. It is the only one of which an aeronaut can dream in the present state of the industry; and steerable balloons with electric motors, especially as they were fifteen or twenty years ago, could have led to no result. That is why the Tissandier brothers gave them up." In spite of the recent immense improvements made in the steam-engine it would not have been able to decide me in favour of steerable ballooning. Motor for motor it is, perhaps, better than the petroleum motor, but when you compare the boiler with the carburator the latter weighs grammes per horse-power while the boiler weighs kilogrammes. In certain light steam-motors, that are lighter even than petroleum motors, the boiler always ruins the proportion. With one pound of petroleum you can exert one horse-power during one hour. To get this same energy from the most improved steam-engine you will want many kilogrammes of water and of fuel, be it