Berget, 1909, Conquest of the Air, p. 9:
In the early days of steam power, motors were of considerable weight. The engine of the Sphinx, the first steamship in the French Navy, weighed more than 1000 kilogrammes per horse-power, and even thirty years ago steam motors weighed some 100 kilograms per horsepower. Hence the first steam engines were no more suitable for the propulsion of aerostats than human effort, to say nothing of the danger of installing a boiler heated by coal beneath an envelope inflated with hydrogen, an eminently inflammable gas.
Nevertheless, steam was the power used in the first motor employed in a balloon. Its application was essayed in 1852 by the engineer, Henry Giffard. Instead of using the steam motors already in existence, he had one of 3 horse-power, expressly built for his experiment; he succeeded in reducing the weight per horsepower to 53 kilogrammes; this was a remarkable achievement at the time and an enterprise of extraordinary audacity, taking its dangers into account. But the steam engine was very soon abandoned, owing to the risk of fire, and aeronauts adopted the electric motor, which, from 1880, was the recognized motor of the future.