1901.] on History and Progress of Aerial Locomotion. 491 



parts. Seven different forms were tried, the last and most successful 

 ones having a number of wings, sometimes as many as five pairs 

 placed one above the other. In the early forms the movements of 

 the body in balancing amounted to five inches, in the later ones they 

 were reduced to two inches, and finally to one inch. 



Mr. Chanute worked in conjunction with Mr. Herring, and the 

 last, and in many ways most successful, machine experimented on was 

 a two-surfaced machine invented by the latter. This, too, was pro- 

 vided with movable parts for automatically regulating the balance, 

 and was taken, in 1897, to Dune Park, where the sand-hills formed a 

 safe experimenting ground. Many glides were made of from 150 to 

 300 feet, in winds varying up to 31 miles an hour (nearly 1^ times 

 the greatest wind-velocity in which Lilienthal experimented), and no 

 accidents occurred, although on three occasions the machine was 

 struck by gusts of wind from above. The longitudinal balance was 

 perfect, no movement being required to right the machine when wind- 

 fluctuations occurred in the line of motion, and in a side wind the 

 movements of the body were much reduced by the automatic arrange- 

 ment. The best glide was one of 927 feet, performed in 48 seconds 

 by " quartering," i.e. sailing in a direction parallel to the side of a hill 

 up which the wind was blowing. Several of Mr. Chanute's friends 

 tried the machine, and found it easy to glide with. 



These experiments of Messrs. Chanute and Herring bring us nearer 

 to a solution of the problem of dynamic flight, i.e. directed motion 

 through air without the'assi stance of balloons. It has, no doubt, been 

 possible for Lilienthal and Pilcher to balance themselves in the air 

 by their own agility, but directly we add a motor to a gliding machine 

 the increased weight makes the effort far more difficult. It is only by 

 reducing the exertion of balancing to a minimum, that we can hope 

 to gain the mastery of a machine carrying its own motive power. 

 On the other hand, the conditions of balance and stability of a 

 propeller-driven machine may differ essentially from those of a 

 mere gliding machine. In the latter, the only propelling force, due 

 to gravity, acts in a direction fixed in space, while the propelling 

 force due to a motor-driven screw acts in a direction fixed relatively 

 to the machine. 



Now, all our preconceived notions lead us to think that the 

 addition of a propelling force of this character, so far from increasing 

 the difficulty of maintaining equilibrium in the air, may materially 

 improve the stability of the machine, and Mr. Herring states that 

 this view has been borne out by experiments which he has made with 

 models. While automatic balance and stability are the first factors 

 to be secured in attempts to solve the problem of flight, it is im- 

 portant that these should not be investigated on gravity-propelled 

 machines alone, but that the effects of a motor should be experi- 

 mentally determined as soon as such experiments can be carried on 

 in safety. 



