“…yet to be navigated…”

From Buchanan’s Journal of Man, June 1887:

The air is certainly yet to be navigated when a sufficient amount of power can be concentrated in the machine, but at present we can do little more than float with the wind. It is probable that an engine sufficiently strong, built of the best steel, and propelled by the explosive power of gun cotton, or some similar explosive, would overcome the difficulty. If I were to construct such an engine I would substitute for the lifting power of a balloon that of a sail acting as a kite.