24 
MR. G. T. WALKER OK BOOMERAKGS. 
screw propeller or a windmill. The direction of the twist is such that rotation about 
a normal to the plane tends to set up linear velocity of the boomerang in the direction 
of the vector representing that rotation. These two peculiarities will in future be 
referred to as the “ rounding ” and the twisting.” 
A weapon of this type is thrown in a hori^^ontal direction in such a way as to 
impart considerable rotation in the vertical plane containing its initial direction of 
motion ; the more convex surface is towards the thrower. The plane of rotation 
leans slowly over to the right {i.e., the vector representing the spin begins to point 
slightly upwards) and the path curls to the left. The projectile proceeds to describe 
a loop whose longer diameter is about fifty yards ; it gradually rises until it reaches 
a height which is usually about thirty feet from the ground, travels horizontally for a 
time, and then gradually sinks to the earth. 
The change in the ang’ular motion has throughout the flight continued unaltered 
in character ; the inclination of the ])lane of rotation to the horizon has steadily 
diminished from a right angle to zero, and the axis of the spin has veered continually 
to the left (as seen from above) in such a manner that as long as the linear velocity 
remains large, the angle between the direction of motion and the plane of rotation 
is small. 
In the accompanying diagram (figs, 2, 3) a plan and elevation of this, the simplest 
form of path, is given. An attem]3t is made to indicate the inclination of the axis of 
rotation by representing at intervals the projection of a line of constant length drawn 
along that axis. 
If it be not desired to make so large a loop as that described, it is fairly eas}" to 
get the boomerang to describe a circle of thirty-five yards in diameter, without ever 
rising to more than twehm feet from the earth. 
In the more complicated paths, as long as the velocity remains considerable, the 
manner in which the plane of rotation and the direction of motion change is precisely 
the same as in the simpler cases; it is the rates of change that differ. The graceful 
gyrations that a boomerang performs on its downward course, if the linear velocity 
dies out while it is high in the air, present little or nothing that is new in principle. 
It is in the explanation of the earlier motion that the problem really lies, and the 
observation of actual flights makes it clear that their character is deducible wdien the 
