ARTIFICIAL FLIGHT. 543 



ceptible downward velocity ; it is, therefore, constantly 

 striking air a^ rest, and accordingly is much more retarded 

 than it would be by making its way constantly through the 

 air that it has set in motion. 



The second result which Professor Langley and Mr. 

 Maxim's experiments proved was this : the horse-power 

 required to sustain a given weight in horizontal flight by 

 means of an aeroplane of given dimensions is less for high 

 speeds than for low ones. In other words, the faster the 

 aeroplane travels, the less energy is required to keep it up 

 in the air for the same length of time. This fact doubtless 

 accounts for the high speeds at which birds fly, and it de- 

 pends upon the same principle as the first result, namely, 

 that the more rapidly the plane moves, the more it comes 

 into contact with fresh particles of air at rest. 



As regards the variation of the air pressure according 

 to the inclination of the plane the general result of Pro- 

 fessor Langley's observations was to confirm the empirical 

 formula previously enunciated by Duchemin. 



From the experiments of Professor Langley, it also 

 appears that a rectangular aeroplane moving perpendicularly 

 to its longest side experiences greater support from the air 

 than it would do if it were moving in a direction parallel to 

 its longest side. A flying machine should therefore imitate 

 the shape of a bird — with narrow wings standing out at 

 right angles to the direction of motion rather than that of 

 a fish. This result is easily explained on the theory that in 

 a wide plane the particles of air coming in contact with the 

 hinder portion have already been set in motion by the fore- 

 most portion, and consequently less reaction can be obtained 

 from them. A further verification of this explanation is 

 afforded by Professor Langley's observations of the position 

 of the centre of pressure, which in all cases is in front of the 

 middle point of the rectangle, showing that the pressure is 

 greatest on the foremost portions. 



The advantages of narrow over wide planes have been 

 most conclusively shown by Mr. Horatio Phillips in some 

 experiments conducted at Wealdstone near Harrow a 

 couple of years ago. " Phillips's Flying Machine," as it 



