GYROPLANES AND HYDROPLANES. 646 



The experiments showed that the sustenance afforded by the 

 air to a rotating gyroplane is nearly as great as that afforded to 

 a disc whose area is the swept area of the gyroplane arms. 



But the distinction which was most strongly marked 

 was the steadiness of the gyroplane as compared with that of the 

 disc. The gyroplanes fell with their axes of rotation vertical, and 

 when they reached the water they did so gently, and continued 

 rotating, the arms skimming on the surface quite prettily ; whereas 

 the discs of equal weight and diameter turned over and over while 

 falling. 



These experiments, and others not here described, have given 

 the writer reason for supposing that increase of speed of revo- 

 lution beyond a certain amount will not be accompanied by any 

 increased sustenance. 



Further experiments are needed to ascertain what particular 

 angular velocity corresponds to the best sustenance effect. 



Of course, merely dropping these objects does not afford 

 a complete comparative test. If propelled through the air the 

 centre of air pressure, both in the case of the disc and the gyro- 

 plane, would be in advance of the centre of gravity, increasing the 

 lifting effect. 



The blades cleave the waves of air much as the blades in the 

 hydroplane experiments, next to be mentioned, cut through 

 waves of water. 



(2) Hydroplane Experiments. — The photographs which accom- 

 panied the paper showed the type of hydroplane used. Sadleir 

 discovered, independently, what Horatio Phillips had discovered 

 vears before, viz., that narrow blades are much more efficient 

 than wide ones, both in water and air. The eddies formed in 

 contact with the surfaces are quickly dropped when the blades 

 are narrow ; there is not the frictional loss that there would be 

 if the eddies were dragged along the rear portions of wider sur- 

 faces ; moreover, the eddying water quickly restores itself and 

 becomes ready for the next blade to operate on, if the blades be 

 not placed too near each other. Sadleir svipports his boat upon 

 a number of transverse blades, flat on the underside, which are 

 tilted upwards in the direction of progress at a slight angle. The 

 blades he used with the boat were 3 ft. 6 in. long by 2 in. wide by 

 about J in. thick at the middle of their width, the blades having 

 knife edges on either side. Sadleir's hydroplane differs from 

 Phillips's in three respects. 1. PhilHps hollowed out the under- 

 side of his blades slightly, while Sadleir keeps his quite flat. 2. 

 Phillips made them wider at the middle than at the ends, whereas 

 Sadleir's planes were of the same width throughout. 3. Sadleir's 

 hydroplane differed from Phillips' in regard to the number of 

 blades employed. Philhps had one fairly large blade, taking 

 nearly all the weight of the boat. It was plated just abaft the 

 centre of gravity of the boat. Then, to steady the boat, he placed 

 a smaller blade near the bow. Both recognised the necessity for 



