eal power when
recently inflated, and before the gas has had time to become
deteriorated by the process of _endosmose_.[B] The whole weight
of the machine and apparatus is seventeen pounds; consequently there
is about four pounds to spare, in order to meet this contingency.

[Footnote A: The frame was made at Mr. Smith's request, by Mr.
Pilgrim, of the Archimedes; the original experimental vessel in which
this mode of propulsion was first tried upon the large scale. Mr.
Pilgrim has been long versed in all that relates to the mechanism of
this instrument, and is indeed a most expert and ingenious artist.]

[Footnote B: _Endosmose_ is that operation by which gases of
different specific gravities are enabled, or rather forced to come
together through the pores of any membranous or other flexible
covering by which it is sought to restrain them. As above referred to,
it is the introduction of atmospheric air into the body of the Balloon
through the pores of the silk, however accurately varnished, by which
the purity of the hydrogen gas is contaminated, and its buoyant power
ultimately exhausted This it is impossible to prevent by any process,
except the interposition of a _metallic_ covering; as for
instance, by _gilding_ the Balloon, which would be effectual
could it be contrived to endure the constant friction and bending of
the material itself.]

Beneath the centre of the Balloon, and about two-thirds of its length,
is a frame of light wood, answering to the hoop of an ordinary
Balloon; to which are attached the cords of the net which encloses the
suspending vessel, and which serves to distribute the pressure of the
appended weight equally over its whole surface, as well as to form an
intermediate means of attachment for the rest of the apparatus. This
consists of a car or basket in the centre; at one end the rudder, and
at the other the Archimedean Screw. The car is about two feet long
and eighteen inches broad, and is laced to the hoop by cords, which
running through loops instead of being fastened individually, allow of
unlimited play, and equalize the application of the weight of the car
to the hoop, as of the whole to the Balloon above. The Archimedean
Screw consists of an axis of hollow brass tube eighteen inches in
length, through which, upon a semi-spiral of 15 deg. of inclination, are
passed a series of radii or spokes of steel wire, two feet long, (thus
projecting a foot on either side) and which being connec