1872.] Artificial Flight: An Aérial Ship. 459 
and the work of the screw per second will be— 
(ae 
Rio (I+a)Rs. 
Consequently the amount of work required to move the 
aérostat is the last quantity plus the amount lost as friction. 
The numerical examples quoted by M. Emile Leclert, 
Architect of the French Navy, in a recent admirable article 
contributed to ‘‘ Naval Science,” will here suit our purpose. 
He shows that the resistance of a thin plane being taken 
equal to 0°665 kilogramme per square metre (14 lbs. per square 
foot) for a speed of 2°22 metres (7°25 feet), the resistance of 
the balloon alone may be estimated at 6 kilogrammes (1°23 lbs. 
persquare foot), and of the entire machine at 11 kilos. (2°25 lbs. 
per square foot). With the values d = 9 metres (293 feet), 
p = 8 metres (264 feet), fraction of speed of each blade at 
the extremity 1-16th, and at the centre of action 1-roth, 
the theory of the screw leads to the conclusion that a=o0'26. 
From this conclusion values are obtained for 2 and T, giving 
as a result that for a speed of 2°22 metres per second, or 
8 kilometres (5 English miles) per hour, the labour of 4 men 
in turning the winch is necessary, and 8 men for a speed of 
2°22 metres + ¥,= 2°80 metres per second, or 10 kilometres 
or 64 miles per hour. These numerical results are quite op- 
posed to the conditions required by Navier’s theory,* being 
a much smaller number of men. 
M. Dupuy de Lome has found that a balloon to be suc- 
cessfully navigated must always be maintained at an equal 
degree of inflation, in order that the resistance to which the 
balloon is exposed in its passage through the air should re- 
main constant, and capable at any moment of being defined. 
The balloon, at starting, being inflated fully with hydrogen, 
the constant degree of inflation is preserved by means of the 
hanging-tubes, H H, Fig. 2. These tubes have the ends 
open, and are pendant about 25 feet below the balloon. As 
the gas expands it forces itself down these tubes, while its 
own pressure in the tube reacts upon the body of gas in the 
balloon, preserving such an excess of interior pressure as 
prevents the shape of the outer covering being altered by 
the force of the wind. Still further to maintain a constant 
surface there is provided a small internal balloon (termed a 
ballonnet), which, as the gas escapes, through diminution of 
* Memoires de l'Institut de France, vol. xi. 
