34 On Aerial Navigation. 
were such as to bear intense condensation sufiicient to preserve 
the form of the prow under this load of pressure. This neces- 
sity of balloons to bear considerable internal and external pres- 
sure will oblige these machines to be made of strong materials, 
and to be braced by a wide net of cordage. It will likewise be 
necessary to make them in several compartments, like the sto- 
machs of a leech, the power of the same cloth to resist conden- 
sation being inversely as the diameters of the containing bag. 
This additional weight will of course in the same degree diminish 
the supporting power: however, it may be practicable by means 
of tubes to each compartment, the mouths of which open exter- 
nally to any required portion of the whole direct resistance of 
the wind, so to proportion the internal pressure, as only slightly 
to exceed the external in these respective compartments, and 
thus much of the strain may be avoided. The pressure of the 
atmosphere upen the skin of a moderate sized man amounts to 
about eight tons ; but being balanced by an internal elasticity of 
equal amount, his lungs play without difficulty, and no strain is 
felt on any part of his skin. The necessity of having several 
compartments in large balloons, though an evil as to weight, is 
fully compensated for by the additional security it bestows :—by 
this structure, an accidental rupture of one portion would not 
cause a precipitate descent, as the floatage may be restored by a 
commensurate discharge of ballast, or of goods, in case of per- 
sonal danger to the crew. The front or prow portion may be 
made of the strongest materials, and the hinder and middle por- 
tion of those duly proportioned to the stress they have to sustain ; 
whereas, if all the air be in one vessel, every part must be alike 
capable of bearing the strongest strain. 1 would not have en- 
tered so minutely into these points, so much in advance of the 
present experimental state of the subject, were it not that the 
reluctance that is felt by some persons to aid experiments upon: 
balloons, arises from a hasty conviction that the difficulties at- 
tending this subject are so great as to preclude all hopes of ul- 
timately overcoming them: I wish to allow all the obstacles their 
fair weight, but to meet them by such expedients as their nature 
permits of, in doing which I fear I may have already trespassed 
too much upon your pages; and shall therefore conclude this 
paper with a very brief enumeration of the leading points that 
ought to induce experiments upon balloons to be made. They 
offer a direct swift and easy floatage from any one point to every 
other on the face of our globe. ‘Their relative resistance de- 
creases inversely to their power of support; so that the large 
balloon of fifty tons formerly described, will meet with no more 
resistance than the bird from which its form is taken, weight for 
weight, Every ton of decomposed water gives two tons of float- 
ing 
