178 TENTH ANNUAL REPORT OF 



bottom up, and yet tlie axis of the spheroid remains parallel to itself, 

 with the elevated end directed towards you. 



Fig. 2. Fig. 3. 



^ 



'S^ 



Friction on the pivots, and resistance of the air, will cause small 

 changes of direction, especially if I move the frame violently. ^^' 



If a body, therefore, were made to revolve on an axis, it might be 

 carried or driven anywhere into space, without ever changing the 

 position of its plane of rotation, unless the forces applied should act 

 unequally on the parts of the body. 



We find an elegant illustration of this tendency to parallelism of axis 

 in the boomereng, a curious missile used by the natives of New South 

 Wales, an account of which is given by Captain Wilkes in his "Explor- 

 ing Expedition."! It is made of wood, about three feet long, two inches 

 wide, and three-fourths of an inch thick, bent in the middle at an ob- 

 Pj„ 4. tuse angle, somewhat resembling a rude sword. 



(Fig. 4.) The article which I hold in my hand ia 

 :-^^0 an actual boomereng, brought by the explorers, 

 ^^" and belonging to the collections of the Smith- 



sonian Institution. Three or four others may be seen in the National 

 Gallery, in the building of the Patent Office. It is thrown with a rapidly 

 revolving motion, and is said to be very effective both in war and 

 hunting. Those who are skilled in its use can throw it obliquely up- 

 ward so that it will come back to them, or even pass over their heads, 

 and hit any desired object behind them. It would be hardly safe for 

 me to try the experiment here, lest (lacking the skill of the savage) 

 I should hurt either you or myself. I can with less hazard, project 

 these models, made of stiff card, and only three or four inches long. 

 Holding one of these with the obtuse angle between my thumb an(;l 

 finger, I snap the end forcibly, so as to send it off obliquely upward, 

 with a swiit rotation in its own plane, and you perceive that instead 

 of describing the usual path of a projectile, after completing its ascent, 

 it returns in the same plane, and falls near me. If several be thus 

 snapped off" in different directions, occasionally one will perform an 

 awkward somerset, but most of them will come back to me. It is 

 that tendency (already spoken of) in a rotating body, to preserve its 



this lecture is of more simple construction, the orbit-rod and the third ring being dis- 

 pensed with, as they are wholly unnecessary for the illustration of composition of rotary 

 motions. 



« In figures 1, 2, 3, the spheroid is seen maintaining the same position, while the frame 

 is placed in various positions. 



t For a description of the boomereng, and its uses, see Captain Wilkes's " Narrative of 

 'the United States Exploring Expedition," vol. II, pp. 191, 192. 



