258 



AERONAUTICS. 



speed, with which the screw is driven, is increased. The 

 screw in this manner is self-adjusting, and extracts a large 

 percentage of propelling power, with very little force and 

 surprisingly little slip. 



A similar result is obtained if two finely graduated angular- 

 shaped gutta-percha or steel plates be placed end to end and 

 applied to the water (vertically or horizontally matters little), 

 with a slight sculling figure-of-8 motion, analogous to that 

 performed by the tail of the fish, porpoise, or whale. If the 

 thick margin of the plates be directed forwards, and the 

 thin ones backwards, an unusually efi*ective propeller is pro- 

 duced. This form of propeller is likewise very effective in air. 



CONCLUDING EEMAEKS. 



From the researches and experiments detailed in the pre- 

 sent volume, it will be evident that a remarkable analogy 

 exists between walking, swimming, and flying. It will 

 further appear that the movements of the tail of the fish, and 

 of the wing of the insect, bat, and bird can be readily imi- 

 tated and reproduced. These facts ought to inspire the 

 pioneer in aerial navigation with confidence. The land and 

 water have already been successfully subjugated. The realms 

 of the air alone are unvanquished. These, however, are so 

 vast glnd so important as a highway for the nations, that 

 science and civilisation equally demand their occupation. 

 The history of artificial progression indorses the belief that 

 the fields etherean will one day be traversed by a machine 

 designed by human ingenuity, and constructed by human 

 skill. In order to construct a successful flying machine, it is 

 not necessary to reproduce the filmy wing of the insect, the 

 silken pinion of the bat, or the complicated and highly differ- 

 entiated wing of the bird, where every feather may be said 



