FORECASTING THE PROGRESS OF INVENTION. 313 



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 efl&cient 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 

 aerial 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, aerial 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 blow- 

 ing 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 convey- 



TOL. LI. 24 



