Page:Popular Science Monthly Volume 51.djvu/325

Rh be considerably reduced, but this is doubtful; and if it can, it probably would not be any benefit, since, if the area of the planes is reduced, the pressure must be increased, and this would result in a less efficient application of the energy required to keep the ship in the air. Another mistaken notion that is accountable in a great measure for the belief in the wonderful possibilities of aërial navigation is that great velocity could be obtained. This assumption is entirely erroneous, and as a matter of fact it can be easily shown that higher speed can be attained on a railroad. As is perfectly well known, the principal obstacle that stands in the way of extraordinary velocity on railroads is the resistance of the atmosphere, and this would be very much greater in the case of an air ship owing to the increased size. The cross-section of a train of cars is less than one hundred and fifty feet, while that of an air ship of the same carrying capacity would probably be ten times as great if not more, and the power required to overcome atmospheric resistance would be in about the same proportion. From this it can be seen that the energy necessary to propel the ship, without saying anything about that required to keep it in the air, would be many times greater than that required to drive a train of cars at the same speed; hence, as a means of rapid transit, aërial navigation could not begin to compete with the railroad.

There is another direction in which the air ship would be seriously defective, and this is almost always overlooked, and that is in the matter of making landings. Being a large body, it would necessarily be unwieldy, and its motion in any direction could not be arrested in a very short space of time; therefore it could not make a landing within a limited area. In a dead calm it could probably be lowered in nearly a vertical line, and thus make a landing in a contracted space, but if the wind were blowing even at a moderate velocity the case would be different. As the wind is always blowing more or less, and as it frequently changes its course in a few seconds, the ship would be tossed about quite lively before it reached the ground. If it came down at the rate of three hundred feet per minute, which is a high velocity, and the wind were blowing at the rate of ten miles per hour, the side drift would be three times as great as the vertical descent; and if this were counteracted by imparting a velocity to the ship equal to that of the wind and opposed to it, the side draught would be doubled if the direction of the wind should suddenly reverse. It must therefore be evident that to be able to make a landing safely, without running the risk of colliding with church steeples and modern sky-scrapers, it would be necessary to have a large open space, and in order that the passengers might not have to walk a large portion of the length of their journey