MR. a. T. WALKER ON BOOMERANGS. 
41 
of rotation may point at the outset rather upwards, and the initial direction of 
motion is slightly uphill. 
As the theoretical angular velocities indicate, there will be an increase in the value 
of and this leads to the plane of rotation being horizontal when the implement 
passes over the thrower’s head at E. The angular velocity along the axis OX will 
then turn the path to the right along EF, \vhile implies that the body rises from 
E to F. After a short time the forward velocity has diminished so far that the 
descent from F to the ground is made quite slowly, under the influence of gravity 
checked by the rotation of the boomerang in a nearly horizontal plane. 
Figs. 10, 11 illustrate the magnitude of the changes in the trajectory that are 
rendered possible by small variations in the shajae of the missile. This path was 
traced by a boomerang which subsequently warped to a slight extent in such a way 
as to increase the tv/isting; the natural flight then became the figure of eight of the 
two jirevious diagrams. 
Through the kindness of Mr. 0. Eckenstein, I have recently had the opportunity 
of seeing and throwing some boomerangs made by him, in which rounding was 
present, but no twisting; the angle between the arms was considerably more obtuse, 
the size increased, and the weight doubled. 
An examination of the equations (3-7) will show that if the value of cos 6 be 
increased, the term due to gravity might be expected to replace for the most part 
that due to the twisting ; further, as the angle between the arms is larger, a given 
amount of rounding will produce a greater effect in diminishing 
When the proportions are rightly chosen, I have not found it difficult to obtain a 
return path ; the plane of rotation is initially inclined at 15° instead of 90° to the 
horizon, and with a decidedly smaller forward velocity as much spin as possible must 
be imparted 
Tn the hands of one accustomed to its use, a boomerang of tins type is capable of 
extremely interesting flights. For the remarkable diagrams (figs. 12, 13) which 
illustrate one of these, I am indebted to Mr, Eckenstein. 
VOL. cxc. —A. 
