The French Zodiac types of "aerial runabout" displace 700 cubic
meters, carrying one passenger with coal gas or two passengers with a
mixture of coal gas and hydrogen. The motor is four-cylinder, sixteen
horse-power, water-cooled. The stern screw, of seven feet diameter,
makes 600 turns per minute, giving an independent speed of nineteen
miles per hour. The machine can remain aloft three hours with 165
pounds of supplies. It costs $5000. Hydrogen costs not far from a cent
per cubic foot (twenty cents per cubic meter) so that the question
of gas leakage may be at least as important as the tire question with
automobiles.
[Illustration: THE ZODIAC NO. 2
May be deflated and easily transported]