chimerical in its form, looked at in view of the conditions of
aerial navigation, but much more singular. Galien describes his
air-boat, in 1755, in his little work entitled, "The Art of
Sailing in the Air." His project was a most extraordinary one,
and its boldness is only equalled by the seriousness of the
narrative. According to him, the atmosphere is divided into two
horizontal layers, the upper of which is much lighter than the
lower. "But," says Galien, "a ship keeps its place in the water
because it is full of air, and air is much lighter than water.
Suppose, then, that there was the same difference of weight
between the upper and the lower layer of air as there is between
the lower stratum and water; and suppose, also, a boat which
rested upon the lower layer of air, with its bulk in the lighter
upper layer--like a ship which has its keel in the water but its
bulk in the air--the same thing would happen with the air-ship as
with the water-ship--it would float in the denser layer of air."

Galien adds that in the region of hail there was in the air a
separation into two layers, the weights of which respectively are
as 1 to 2. "Then," says he, "in placing an air-boat in the region
of hail, with its sides rising eighty-three fathoms into the
upper region, which is much more light, one could sail
perfectly."

But how to get this enormous air-boat up to the region of hail?
This is a minor detail, respecting which Galien is not clear.

From the labours of Lana and Galien, with their impossible flying
machines, the inventor of the balloon could derive no benefit
whatever; nor is his fame to be in the least diminished because