64 PHYSICS. 
reached, which is done with impunity. The anchor D serves to attach it to 
the earth. 
Pl. 18, fig. 73, represents an ordinary balloon, A, with its valve at C, 
and to which is suspended the car D by means of the network F and the 
cords E, E, E, E.  B is the hose through which the balloon is filled. Fig. 74 
represents the copper balloon constructed in Paris according to Marey 
Monge’s plan fer conducting physical experiments in the upper strata of 
the atmosphere. The segments are of copper plate, about one eighth of 
a line thick, and the joints well soldered. The balloon is thirty feet in 
diameter, weighs 800|bs., and contains about 100lbs. of hydrogen gas. 
The guidance of the balloon in any given direction has up to the pre- 
sent time not been accomplished ; a rise and fall can indeed be effected, 
but not a horizontal motion, this being dependent upon the currents of the 
wind. For practical purposes the balloon is therefore inapplicable, and 
except for scientific purposes, its employment by the French army in mi- 
litary reconnoissance was the only application ever made of it. Experi- 
ments to effect a guidance of the balloon, and a motion in a determinate 
direction, have indeed been frequently made, and it may perhaps be 
advisable to refer in brief terms to severa] contrivances proposed for this 
purpose. Pl. 17, fig. 41, represents the Flying Machine of Henson (air 
steamboat), which, however, is essentially nothing but a great parachute, 
and has by no means answered its intention. AA are two wings, each 
one hundred and fifty feet long and thirty feet broad, constructed of iron 
werk, over which is stretched a silk or linen covering ; this latter consists 
of three parts, which can be opened or shut by means of arope. The wings 
are sustained by the iron posts, B, B, and cords stretched over them, and 
are immovably attached to the firm middle part. The motive power consists 
of the fan wheels, D, D, set in rapid motion by the steam-engine, G; to this 
latter is attached the car for passengers, &c. The change of direction, in 
a horizontal plane, is produced partly by a rudder, partly by the tail, E, 
which is composed of a fan-shaped frame covered with silk, and movable 
freely about F. The visionary nature of this arrangement, presented here 
only as a curiosity, is evident at the first glance; any practical value is 
entirely out of the question, for the reason that no balloon is employed in 
its construction, but the machine must begin its journey from a high tower 
or lofty mountain, which journey then can be nothing else than a long 
protracted fall without any possibility of ascent. The aerial ship proposed 
by the Englishman Partridge, some years ago, and by him called Pnewmo- 
drome, certainly promises better results. It is represented in various de- 
tails on Pl. 17, figs. 42—48, fig. 42 being a half-side view, fig. 43 a half 
longitudinal section, fig. 44 a vertical transverse section, and fig 45 an 
end view, with the balloon partly omitted. The principal parts of the 
balloon consist of: 1. the balloon, A, of air-tight india rubber cloth, a 
square yard of which weighs about one pound, spheroidal in shape, and 
whose length, breadth, and height are as 7: 4:2. For the filling the in- 
ventor employs pure hydrogen gas. As, however, the inclosed gas ex- 
pands greatly at a height whére the pressure of the atmosphere is much 
238 
