An object offers as much resistance to the air as the air does to
the object. You may see that the beating of its wings against the
air supports a heavy eagle in the highest and rarest atmosphere,
close to the sphere of elemental fire. Again you may see the air in
motion over the sea, fill the swelling sails and drive heavily laden
ships. From these instances, and the reasons given, a man with wings
large enough and duly connected might learn to overcome the
resistance of the air, and by conquering it, succeed in subjugating
it and rising above it. [Footnote: A parachute is here sketched,
with an explanatory remark. It is reproduced on Tav. XVI in the
Saggio, and in: _Leonardo da Vinci als Ingenieur etc., Ein Beitrag
zur Geschichte der Technik und der induktiven Wissenschaften, von
Dr. Hermann Grothe, Berlin_ 1874, p. 50.]

Of mining.