Hence the impossibility of making practical use of this mode of aerial locomotion.
With regards to the means employed to give the aerostat its motion a great deal of progress had been made.

For the steam engines of Henry Giffard, and the muscular force of Dupuy de Lome, electric motors had gradually been substituted.

The batteries of bichromate of potassium of the Tissandier brothers had given a speed of four yards a second.
The dynamo-electric machines of Captain Krebs and Renard had developed a force of twelve horsepower and yielded a speed of six and a half yards per second.
With regard to this motor, engineers and electricians had been approaching more and more to that desideratum which is known as a steam horse in a watch case.

Gradually the results of the pile of which Captains Krebs and Renard had kept the secret had been surpassed, and aeronauts had become able to avail themselves of motors whose lightness increased at the same time as their power.
In this there was much to encourage those who believed in the utilization of guidable balloons.

But yet how many good people there are who refuse to admit the possibility of such a thing! If the aerostat finds support in the air it belongs to the medium in which it moves; under such conditions, how can its mass, which offers so much resistance to the currents of the atmosphere, make its way against the wind?
In this struggle of the inventors after a light and powerful motor, the Americans had most nearly attained what they sought.