MR. G. T. WALKER OK BOOMERANGS. 
37 
It is interesting to compare these results with those belonging to a boomerang 
whose arms include an angle 120°. 
Thus, taking 
2 a = 120 °, U = 2000 , n = 50, kU = 7, XIJ'’ = 5, 
we obtain 
9.,= 
8 .9 700 
— “T 
P ^ 
-f 1 „ 3 cos 0 
O 
il 
3.8 2000 
P 
3 . 1 cos 9 
>. . . . 
. . (6), 
11 
720 380000 
P ^ 
“ 720 cos 9 
J 
while the second estimate of .‘cU, namely 5, yields 
^ 10.7 , 510 , . N 
n. = —-d- — + cos 9 
^ p T 
4 .6 2300 
P ^ 
860 440000 
3.5 cos 0 y 
w — 
850 cos 6 
j 
(7). 
The values of p and r in practice are usually comparable with 20 and 800 
respectively. 
That the form of the equations is correct, at any rate as regards a first approxi¬ 
mation, is confirmed by the experience gained in making and throwing upwards of 
seventy boomerangs of different weights, shapes, and sizes. 
If, for example, one of these does not curl sharply enough to the left (i.e., is 
negative, but not numerically large enough), it is found that increasing the twist 
{i.e., diminishing r) will produce the desired effect, A further result will be an 
increase in and a coiisecpient tendency to skythis may be corrected by 
makino; the difference of curvature of the two surfaces more pronounced ; a diminution 
in p will thus bring about a diminution of Oi- 
Some of these implements were made with the express object of verifying 
particular terms. If tliere be no twist, and 6 = 7 r/ 2 , while p is not extremely largCj 
is negative and positive; if, on the other hand, p is infinite, but r is finite and 
positive, flj is positive and n .2 is negative. 
From experiments made in this manner, with a somewhat smaller spin than that 
assumed above, I have deduced the formulse 
2 
0 
— -f — -b 2 cos 0 I 
p T 
1200 cos 0 
9. 
