It must not be supposed that the invention of the steerable balloon was greatly in advance of that of the heavier-than-air machine.
"The Mastery of the Air"
William J. Claxton
At length, however, the internal-combustion engine, such as is used in motor-cars, arrived, and it became at last possible to solve the great problem of constructing a really-serviceable, steerable balloon.
"The Mastery of the Air"
William J. Claxton
Indeed, the cause of the long delay in the construction of a steerable balloon was that a suitable engine could not be found.
"The Mastery of the Air"
William J. Claxton