books of this series, the construction of Tom Swift's airship, the Red Cloud, and as the Black Hawk was made in a similar manner to that, we will devote but brief space to it now. As the story proceeds, and the need arises for a description of certain features, we will give them to you, so that you will have a clear idea of what a wonfderful craft it was.
Sufficient to say that there was a gas bag, made of a light but strong material, and capable of holding enough vapor, of a new and secret composition, to lift the airship with its load. This was the dirigible-balloon feature of the craft, and with the two powerful propellers, fore-and aft (in which particular the Black Hawk differed from the Red Cloud which had two forward propellers);—with these two powerful wooden screws, as we have said, the new ship could travel swiftly without depending on the wing planes.
But as there is always a possibility of the gas bag being punctured, or the vapor suddenly escaping from one cause or another, Tom did not depend on this alone to keep his craft afloat. It was a perfect aeroplane, and with the gas bag entirely empty could be sent scudding along at any height desired. To enable it to rise by means of the wings, however, it was necessary
