II. Oil Boomerangs. 
By G. T. Walker, M.A., B.Sc., Felloiv of Trinity College, Cambridge. 
Cominmiicated by Professor J. J. Thomson, F.B.S. 
Received Mai’ch 15,—Read April S, 1897. 
The attemjTs that have hitherto been made to explain the fliglit of a boomerang 
have in general been of a somewhat fanciful nature. 
Exception must be made in the case of such papers as those of Werner Stille, 
“ Versuche und Eechnungen zur Bestimmung der Bahnen des Bumerangs” (Poggen- 
DORFF, ‘ Annalen der Physik,’ Bd. 147, 1872), and of Edmund Gerlach, ‘'Ableitung 
gewisser Bewegungsformen geworfener Scheiben aus dem Luftwiderstandsgesetze ” 
(‘Zeitschrift des Deutschen Yereins zur Fbrderung der Luftschifffahrt,’ Heft 3, 188G). 
Ill the latter, which is the most noticeable contribution to the subject with which I 
am acquainted, the author gives an explanation in general terms of some of the 
effects of the air-resistance upon a symmetrical boomerang : he introduces, however, 
no analytical treatment of the dynamics of the rotating body and neglects entirely 
all consequences of the important deviations from symmetry wdiich I have siibse- 
cjiiently described as “twisting” and “rounding.” AYithoiit one of these a return 
flight is, I believe, imjiossible. 
For an account of the native Australian weapons, and in particular those of ABctoria, 
reference should be made to the very complete descriptions given in Brough Smyth’s 
book, ‘The Aborigines of Victoria,’ vol. 1, pp. 311-318; shorter notices are to be 
found in books of travel, suck as that of Karl Lumholtz, ‘ Among Cannibals,’ p. 50. 
Boomerangs may at the outset be divided into two classes—returning and non¬ 
returning ; it is rather on weapons of the latter of these types that the natives ol 
Australia rely w’hen engaged in war or the chase. A typical returning boomerang 
(see fig. 1) resembles in general outline an arc of a hyperbola, and is about 80 centims. 
in length measured along the curve. At the centre, where the dimensions of the 
cross section (fig. 1') are greatest, the wddth is about 7 centims., and the thickness 
1 centim. ; these dimensions become smaller as the ends are approached. 
As a rule two properties are present. In the first place, the transverse section at 
any point would show that one surface possesses distinctly greater curvature than 
the other; secondly, the arms of the implement must be slightly twisted (from 
coincidence with the plane through each of them) after the fashion of the blades of a 
7.9.97 
