of the Native Australians called the " BoomarangJ* 331 



resistance as the globe. See Sir Isaac Newton's Principia, 

 lib. ii. prop. 34 ; also Vince's Hydrostatics, prop. 29. From 

 page 1 1 of App. to last-mentioned work, it appears that ex- 

 periments prove the resistance aforesaid to be even in a 

 greater ratio than theory teaches, viz. in the ratio of 2*23 : 1 

 nearly 2^: 1, i. e. 9:4. Also, from the same page, we learn 

 that the resistance to the plane side of a semiglobe is greater 

 even than the resistance to the base of its circumscribed cy- 

 linder. Hence we may infer that the resistance to a plane 

 surface moving in a fluid is considerably increased by the cur- 

 vature of the back part of the body. 



6. From a careful attention to these facts, we can have no 

 difficulty in admitting that the plane surface of the kylee suf- 

 fers a resistance, if not twice as great, at least much greater 

 than the curved side ; and consequently, since the forces acting 

 on its two sides are in opposite directions, whatever may be 

 the extent of the resistance to the curved side, it is altogether 

 counteracted and nullified by the superior resistance to the 

 level side. And not only this, but we may also see, as I will 

 show immediately, that the excess of the more powerful over 

 the weaker force remains a free agent, unexhausted, and there- 

 fore capable of bearing the body upwards for a time in op- 

 position to gravitation. 



7. I stated above (3.) that the force which acts on the plane 

 side is for a time superior to gravity ; and before I prove the 

 correctness of this assertion, I may remind you, in connection 

 with this point, of the principles by which is explained the 

 cause that makes a boy's kite hover for hours suspended in 

 the air, notwithstanding its greater specific gravity. You are 

 aware that the kite, by constant tension of a cord attached to 

 it, is made to act on the air, the particles of which, since action 

 and reaction are equal and in opposite directions, react on the 

 kite in a contrary direction, and thus support it against gravi- 

 tation as long as the cord is held tight. 'T is the same prin- 

 ciple which enables a bird to support itself on its wings; and 

 it is worthy of remark, that there is a very striking resem- 

 blance in the shape of a bird's wing to the figure of the body 

 in question. 



8. I shall now proceed to show that the force acting on the 

 plane surflxce is for a time Superior to gravity, or, which is the 

 same thing, that it acts upwards. When the body is projected 

 in any direction, its plane side making with the horizon an 

 angle of 40° or 50^^, and the projector holding the plane side 

 off*, and the curved side towards himself, the plane side, by 

 impinging on the first volume of air, generates, as we have 

 seen (5.), a certain resistance to itself, which is in some ratio 

 to the velocity with which it moves (generally admitted to be 



