516 



BOOMERANGS. 



sails of a windmill, being rotated through 2 J or 3° in the direction 

 of a right-handed screw about the lines B A, B C, as axes. This 



'g-2- 



deviation from the plane is subsequently referred to as the "twist," 

 and the peculiarity that, as seen in the cross section of tig. 2, one 

 face is more rounded than the other, is called the "rounding." 



Boomerangs of the sec- 

 ond type (tig. 3) are about 

 TO cm. long and 7 cm. wide, 

 and have a cross section 

 similar to that of fig. 2. 

 The "'twist'' 1 is in the op- 

 posite direction, involving 

 a left-handed rotation of 

 about 3°. The axes of rotation are now D E, F E instead of E D, E E. 



RETURNING FLIGHTS. 



An implement of the first type is held with the more rounded side to 

 the left and the concave edge forward. It is thrown, with plane vertical, 

 in a horizontal direction, and as much rotation as possible is given to it. 

 The plane of rotation does not remain 

 parallel to its original direction, but has 

 an angular velocity (1) about the direc- 

 tion of translation, and (li) about a line 

 in its plane perpendicular to this. 



The effect of (2) is that the path curls 

 to the left, while owing to (1) the plane 

 of rotation inclines over to the right 

 (i. e. , rotates in the direction of the 

 hands of a clock facing the thrower), and 

 its inclination to the vertical becomes 



comparable with 30° in two seconds. The angular velocity (2) will 

 now imply that the path bends upward as well as horizontally round 

 to the left. 



When the boomerang has described a nearty complete circle its pace 

 has diminished, and it falls to the ground near the thrower. (See 

 figs. 4, 5, in which projections on a horizontal and on a vertical plane are 



Fig. 4.— Plan. 



