S34 On the projectile Weapon of the Native Australians, 



for in that case there would be no supporting power. But let 

 it be granted that it has become only 60° or 70°, and we may 

 easily perceive the effect that will follow. 



12. When gravity begins to act on the body in these cir- 

 cumstances, its plane surface impinges on the column of air 

 beneath, the particles of which immediately react on the plane 

 surface, and by this means cause it to deviate from the per- 

 pendicular to the horizon, down which it had commenced to 

 descend by the force of gravity. And because the plane sur- 

 face is, at this juncture, removed from the projector, and that 

 the resistance is against the plane side, the direction of its 

 deviation from the perpendicular will be towards him. This 

 occurs in the first instant of descent, the same in the second, 

 and so on, until its return to the earth ; with this exception, 

 that the body descends with a velocity increasing at every 

 pointy as it retires from the highest (see Mechanics, Oscilla- 

 tions of Bodies). Hence the amazing velocity with which it 

 moves immediately before reaching the earth. I need scarcely 

 add, that since the two forces causing its return are not uni- 

 form, the line of its descent must be curved. 



13. An additional cause of its returning is the direction 

 (relative to the line of its motion, and relative to its plane side,) 

 in which those particles impinge on its plane side, which pro- 

 duce a greater effect than any of the other particles acting 

 on the same side. The direction to which I allude is the 

 angle of 54° 44?' mentioned above (9.). The annexed figure 

 will render this much clearer than lan- 

 guage can do. B E R is the curve 

 through which it moves ; and each of the 

 lines n a, r d, &c. will represent the 

 angle 54° 44' at which the most powerful 

 particles already spoken of act on the 

 plane side of the body ; for when by 

 the impact of the first series of the most 

 powerful particles on the plane side, the 

 position of that side becomes altered, it is 

 manifest that a change will also be ef- R'b 

 fected in the position, not in the magnitude of the angle, at 

 which the next series of most powerful particles will act on 

 the same side. And because this process continues in the 

 manner represented in the figure, their tendency is evidently 

 to make it return. 



14. It will be observed that as the body descends, the 

 angle of inclination gradually decreases, until the plane side 

 becomes parallel to the horizon. The reason of this, and 

 some other observations, which I intended to offer on the na- 



