W. LE CONTE STEVENS. 45 
was about one-and-a-half horse-power, equivalent there- 
fore to about ten men, while its weight of battery and 
motor together was little over that of threemen. He 
attained a speed estimated to be rather more than six 
miles an hour, but the sail rudder proved to be imper- 
fect, and interfered with his experiment that was other- 
wise successful. A year afterward he made another 
ascent with this balloon and succeeded in attaining a 
Speed about one-third greater. 
Meanwhile MM. Renard and Krebs, officers of the 
French army, were conducting experiments at Chalais- 
Meudon, near Paris, on the conditions requisite for di- 
recting balloons, being guided in their studies by the 
_previous work of Dupuy de Lome. They constructed a 
balloon (fig. 4, page 46) one hundred sixty-six feet long, 
twenty-eight feet in its greatest diameter, with a ca- 
pacity of sixty-seven thousand cubic feet and ascensional 
power of nearly five thousand pounds when inflated with 
hydrogen. The motive power was electricity, as with 
'Tissandier’s balloon. The propeller is fixed to the ex- 
tremity of a long shaft and placed at the front, while the 
rudder, made of cloth, stretched tightly over a frame, is 
placed at the rear. In form it is symmetrical about a 
longitudinal axis, but the tapering is more abrupt at 
front thanrear. The balloonis filled with hydrogen, but 
within it is a subsidiary balloon, connected by a tube 
with the cage below, where air can be pumped in or out 
at pleasure, thus varying slightly the specific gravity of 
the mass as a whole, and enabling the aeronauts to vary 
their elevation at will. 
_ On August 9, 1884, Renard and Krebs ascended with 
this balloon, made a journey of nearly five miles, 
changing direction several times, and returning at the 
end of twenty-three minutes to the point of departure. 
On the eighth of November of the same year, they made 
two successful journeys, in the same afternoon, at- 
