18 
FLANGES OF AUSTRALITES (TEKTITES) 
itself, and the flow structures frequently indicate spiral coiling 
of the flange glass. 
The complex flow patterns in flanges result from the movement 
of cooling glass from the outer edge towards still cooler glass 
in and below the chin. The major flow structures result from 
flowage from the anterior surface of successive streams of molten 
glass ; see Plates I to III. 
The shapes of australites are not those considered as stream- 
lined by physicists, but no other tektites approach a similar 
degree of symmetry, a fact suggesting that these tektites differed 
from australites in physical condition during transit through the 
atmosphere. 
If australites traversed our atmosphere at speeds greater than 
that of sound, the adjacent layers of air in which all frictional 
effects took place would be thin. Since the coefficient of heat 
conductivity in australite glass is low (somewhere between that 
of artificial glass, 0 0005, and that of Darwin Glass, 0 0002), the 
rate of heat transference is slow. Little time was available while 
the australites traversed the atmosphere for diffusion of heat to 
the interior and to rear surfaces. To become plastic the glass 
must be raised to temperatures of 800° C. or higher. In the wake 
of fast-moving australites there would be a region of “dead air” 
where pressures and temperatures were low, and the rear regions 
of the objects would therefore remain cold. 
It has been shown experimentally that no frictional forces 
operate at the poles of a sphere falling through a fluid, that 
pressure is greatest at the front and least at the rear pole, and 
that frictional forces are greatest at the equator. It is therefore 
probable that, during flight, pressure on the anterior surfaces of 
australites caused plastic glass to form ridges which moved 
towards their equators, where these ridges would be crinkled by 
frictional drag developed by turbulences in the adjacent layer of 
air. Flow lines would therefore be contorted or puckered near 
the outer edge of the flange (PL I, 12, and PI. II, 3 and 7). On 
reaching the outer edge of the flange, some of the plastic glass 
was swept towards the posterior surface, probably by eddy 
currents which exerted a smoothing effect, as indicated by the 
smooth posterior surfaces of flanges. Complexities in internal 
structures of flanges, then, resulted from variations in direction 
of eddy currents and in the rate of cooling of successive layers 
of molten glass. The first supplies of glass to a growing flange 
would cool while more fluid glass was flowing in from the heated 
front surface. 
