64 Mr. J. W. Sharper 



parallel to the axis of the boomerang. This agrees with the 

 result in Mr. G. T. Walker's paper in the Phil. Trans, 

 vol. 190, p. 25, viz. : that the latter is about double the 

 former. From this paper have been taken the descriptive 

 details here given, of the form and length and height of 

 range, of the Australian boomerang. 



Considering now, not the rotational motion, but the motion 

 of the C.G. itself, for which purpose the whole mass may be 

 imagined to be condensed into one particle at the C.G., and 

 to be there acted upon by all the air reactions and by its own 

 weight, it will be seen that the third set of components, i. e. 

 those parallel to the axis of the boomerang, impel the C.G. 

 in the direction of this axis, at first moving it leftwards and 

 afterwards lifting it in the air ; whilst the other two sets, 

 with much less effect, check its flight, and very slightly 

 divert it, at first downwards, and then leftwards. Owing to 

 the bent form of the boomerang, it might be thought that the 

 third set of components would have some slight effect in 

 setting up angular momentum about the principal axis 

 parallel to the line of the horns ; but whatever effects in this 

 way they may have will cancel themselves in each complete 

 revolution of the boomerang. 



For non-returning flight (see Mr. Walker's paper) the 

 boomerang is thrown with the principal plane leaning a good 

 deal away from the vertical, outwards towards the right. 

 As before, it steers itself at first towards the left, whilst its 

 plane steadily becomes more and more nearly horizontal, the 

 axis leaning more and more over towards the right. When 

 the principal plane has passed the horizontal, and the axis is 

 leaving the vertical, and inclining to the right of it, the 

 boomerang will then begin to steer itself also to the right ; 

 and hence the path is now composed of two curves joined at 

 a point of inflexion, the first concave towards the left, and 

 the second concave towards the right. The range is greatly 

 extended by the effect of the twist, through the 3rd set of 

 components of the air reactions, in raising the missile and 

 maintaining it in the air, and also by the peculiar action of 

 the convex form of the surfaces, especially that of the upper 

 surface, which is the more curved of the two. As explained 

 above, this, in conjunction with the bent form of the weapon, 

 through the action of the 2nd set of components, causes the 

 axis to incline backwards towards the thrower, as indeed 

 do also the 3rd set of components ; hence the forward edge 

 tends always to lift itself against the air, so that, even if 

 there were no twist, there would nevertheless be a lifting 

 effect arising from the upper, or rightward horn, the speed 



